WJEC GCSE Additional Science Teacher’s Notes
1
Developing scientific
enquiry skills
Scientific enquiry skills need to be developed throughout the course. The various parts of this
chapter should be referred to as the course progresses. It does not form a single ‘unit’ to be worked
through consecutively.
_What is a hypothesis? (pages 1–2)________________
Questions
1. For each person, say
a if the suggestion qualifies as a scientific hypothesis
Jane and Dave’s ideas are hypotheses. Aaron and Rebecca have no clear evidence for their
ideas – they are really only guesses.
b
if it does, say whether you think it is a good scientific hypothesis.
It might be useful here to discuss with the class what makes one hypothesis ‘better’ than
another. Jane has clear evidence for her hypothesis and it would be easy to test by
experiment. It is a good hypothesis. Dave’s is not a particularly good hypothesis because
the evidence he uses is doubtful. It would be OK if Jane’s mum only ever drank one type of
white wine and one type of red, but that is unlikely.
2. Explain the differences between a hypothesis, a prediction and a theory.
A hypothesis offers an explanation but a prediction does not. A hypothesis has not been
extensively tested, while a theory has been extensively tested and has been consistently
supported by experimental evidence.
This question is a good exercise in communication skills. It is not sufficient for the students
to simply explain what a hypothesis, a prediction and a theory are – they must compare them
and explain the differences.
_How do you devise a hypothesis? (pages 2–4)_______
TASK Devising a hypothesis (page 4)
1. Suggest at least two possible hypotheses that might explain Prince’s behaviour.
Possible hypothesese are:
1) Prince can smell his owner approaching from a long distance away.
2) Prince hears the car when it is some distance away and can tell his owner’s car from
others.
3) Prince’s biorhythm means he can roughly ‘tell the time’, and he has learnt that his owner
comes home at a certain time each day.
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WJEC GCSE Additional Science Teacher’s Notes
2. Pick one of your hypotheses and suggest how you might test it.
Hypothesis 1 could be tested by flooding the room with strong-smelling air freshener to
‘mask’ the detection of the owner’s smell, and see if Prince still goes to the window (it
would be difficult to be certain if the masking works, however). Hypothesis 2 could be
tested by getting the owner to drive home in a different car, and see if Prince still goes to the
window. Hypothesis 3 is easy to test if the owner arrives home significantly earlier or later
than normal. If Prince still goes to the window just before his arrival in those circumstances,
it is clearly not related to the time.
_Drawing conclusions – is my hypothesis supported?__
(pages 5–7)
Questions
3. Natalie had a hypothesis that wet paper could hold less weight than dry paper. She tested paper bags,
adding weight 10 g at a time until the bag broke. She tested 10 dry bags, and then soaked 10 similar
bags in water and tested them. In every single case, the wet bags broke with less weight in them than
the dry bags. What should Natalie’s conclusion be?
The correct answer is
b
Her hypothesis is supported.
4. Glyn had a hypothesis that a certain brand of insulated mug did not actually keep drinks any warmer
than a normal ceramic mug. He timed how long it took water to cool by 10 °C in the two types of mug.
He ran the test 50 times. On average, the water took 6 minutes longer to cool down in the insulated
mug, and in all 50 tests the water in the ceramic mug cooled quicker. What should Glyn’s conclusion
be?
The correct answer is
d
His hypothesis should be rejected.
TASK Can people tell the difference between butter and a
butter spread (page 7)
This is a difficult exercise. It has to be difficult because the aim is to test if pupils can draw
appropriate conclusions from ‘real’ science results, which are very often not completely ‘black
and white’. There would be little point giving pupils data that very clearly supported or
contradicted a hypothesis.
1. Patrick and Isobel’s hypothesis was ‘People cannot tell butter spread from butter’. The alternative is
‘People can tell butter spread from butter’. Comment on the evidence for each of these hypotheses.
‘People cannot tell butter spread from butter’ – Pure guesswork would lead to roughly 50%
success. Although there is a 56% success rate here, the difference from 50% is not big
enough to reject the hypothesis, but it is not supported by this evidence.
‘People can tell butter spread from butter’ – despite the 56% success rate, the difference is
not big enough to clearly support this hypothesis. In addition, the results are quite variable
from person to person. There is weak evidential support, but overall the results are
inconclusive.
2. What is your conclusion from these results?
The results do not support Patrick and Isobel’s hypothesis, but the evidence is too weak to
reject it.
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WJEC GCSE Additional Science Teacher’s Notes
_ How do scientists evaluate their methods?_________
(pages 8–10)
Question
5. In the experiment described at the bottom of page 9, how many readings do you think the person doing
the experiment should have taken?
20–30 readings should have been taken. Accept 20, 30 or anything in between.
TASK Are you a scientist yet? (page 10)
Possible hypotheses are:
Woodlice tend to be found in dark places.


Woodlice move away from the light.
Woodlice move more in the light than in the dark.
It is very important that people notice warning signs. Warning signs are nearly always red.

The colour red is more noticeable than other colours.
Cheap brands of fizzy drinks seem to go ‘flat’ quicker than more expensive brands.


Cheap drinks have less carbon dioxide in them than expensive ones.
The bottles of cheap drinks are less air tight than expensive brands.
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WJEC GCSE Additional Science Teacher’s Notes
2
Cells and cell processes
_What are cells? (pages 12–13)___________________
Note that the structure of the electron microscope does not need to be learnt.
_Are cells the same in plants and animals?___________
(pages 13–15)
PRACTICAL Can you find cells? (page 15)
Note that sampling your own cheek cells is perfectly acceptable on health and safety grounds.
Long ago, when HIV first became a problem, some local authorities asked schools not to do
this, but the risk is virtually insignificant and there is no reason why this technique should not
be practised.
Pupils should be allowed free investigation of the celery to discover what they can. Other
plant material may be added or substituted. Celery is particularly good for looking at xylem
cells, but is not so good for leaf epidermis (Zebrinapendula and Rhoeo discolour are good for
this).
The specification expects pupils to investigate specialisation of cells. Point 4 of the
procedure is therefore important, as the chapter text does not deal with this. No specific
specialised cells are mentioned in the specification, so it does not matter which cells the pupils
investigate.
_Can you call viruses living organisms? (page 16)_____
Question
1. The cell theory says that all living organisms are made of cells. Viruses are not made of cells, yet the
cell theory is still accepted. Suggest why.
Viruses are not considered to be fully ‘living’ organisms and so the cell theory does not apply
to them.
_How are the activities of a cell controlled?__________
(pages 17–18)
PRACTICAL What is the best temperature to wash your
clothes? (page 18)
The answers to questions 1–3 depend upon the pupil’s experimental design and results.
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WJEC GCSE Additional Science Teacher’s Notes
4. What other factors, apart from the effectiveness of stain removal, might influence a decision about
what temperature to use for your wash?
High temperatures are more costly because more energy is used; high temperatures cause
some materials to shrink.
5. Explain why enzymes allow washing at a lower temperature than non-biological detergents.
The enzymes catalyse the chemical breakdown of the stains. The end products are soluble
and so can be removed by water, even at low temperatures. Breakdown of the stains by heat
alone requires higher temperatures.
_ How does the nucleus control the cell? (pages 19–20)
Note that the specification does not require candidates to know the names of the bases in DNA,
referring to them only as A, C, G and T. The names are given here in order to indicate WHY they
are called A, C, G and T.
TASK Discovery of DNA structure (page 20)
This activity is very important. The discovery of DNA is not covered elsewhere in the book but
is required by the specification.
_ How do new cells form? (pages 20–23)____________
Questions
2. Cats have 38 chromosomes, dogs have 78 and wheat has 42. How many chromosomes would you
expect to find in:
a an egg cell of a dog?
39
b
a kidney cell of a cat?
c
a pollen cell of wheat? 21
38
3. Why would meiosis not work as the ‘normal’ method of cell division in the body?
The new cells would only have a half set of chromosomes, and further divisions would
constantly halve that number.
PRACTICAL Observing cell division (pages 22–23)
This is quite a complex, but rewarding, technique. There are risks associated with both the stain
and hydrochloric acid, and ethnoic alcohol and ethano-orcein are both hazardous chemicals. See
Hazcards 38 and 38A.
Ethanoic alcohol is made of 3 parts absolute ethanol to1 part glacial ethanoic acid. Mix just
before use, adding the acid to the alcohol. www.practicalbiology.org suggests using 95%
ethanol instead of absolute, but states that chromosomes may not be as clearly defined.
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WJEC GCSE Additional Science Teacher’s Notes
Ethano-orcein stain is made by grinding 1.5 g of solid orcein with a pestle and mortar. In a
fume cupboard, mix 90 cm3 of glacial ethanoic acid with 110 cm3 of distilled water and bring to
the boil. Pour the boiling mixture over the orcein and stir very thoroughly (still in the fume
cupboard). Leave overnight, then filter and store in a tightly-stoppered dark bottle. An
alternative is lactopropionicorcein stain.
_Do animals and plants grow in the same way?_______
(pages 23–24)
Discussion points
1. What are the advantages to a plant of a branched growth form? Why might a compact form be better
for animals?
Branched growth allows greater spread for light capture (irrelevant in animals). Plants are
sedentary and so cannot escape predators. A branched form allows parts of the plant to be
lost/damaged without destroying the whole. Animals have no need of a branched form and
such a form would inhibit movement.
2. Why is being able to grow throughout life a particular advantage to plants, and why would it not be so
advantageous for animals?
This again could be linked to the need to re-grow parts eaten by animals. It also ensures the
best chance of reaching light. Neither is necessary in animals, and increasing size would mean
constantly increasing food demands, as well as making it difficult to support the body and
possibly to feed. Small animals do not have the adaptations to cope with becoming larger.
Questions
4. Describe the pattern shown in the graph (Figure 2.21).
Growth rate starts very high but declines rapidly until the age of 3–4, then more gradually until
the age of 12. Between the ages of 12–14 the rate increases again, then declines steadily until
the age of 20.
5. Suggest an explanation for the shape of the graph between the ages of 12 and 14.
Puberty occurs and this is associated with rapid growth.
_What are stem cells? (pages 24–25)_______________
TASK How should we use stem cells, if at all? (page 25)
This activity is included to meet the needs of the specification, to discuss the future potential
and ethical issues surrounding stem cell technology.
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WJEC GCSE Additional Science Teacher’s Notes
3
Transport in and out of cells
_What is diffusion? (pages 27–29)_________________
Questions
1. Why are oxygen and carbon dioxide important in living things?
Oxygen is needed for respiration, which provides energy for all living processes.
Carbon dioxide in animals is a waste material. Build up of CO2 can affect the pH of body fluids
which could prevent enzymes working. In plants, carbon dioxide is needed for photosynthesis,
so that plants can make food.
2. How good a model do you think Figure 3.1 is of diffusion? Is it inaccurate in any ways?
It is not a good model! (Note the diagram is not intended as a ‘model’, but just a visual
memory cue.) Diffusion is random movement. This model suggests a force moving the particle
down the gradient.
PRACTICAL ‘Modelling’ diffusion (page 28)
1. The marbles never remain in a group, they always spread out. Explain why this happens.
If the marbles move towards each other, they will collide and bounce off. If they move away
from each other, nothing impedes them, and they move freely. Thus is it easier for the
marbles to spread out.
This is a good exercise for practising thinking and communication skills. Many pupils
will find it difficult to explain the process they see, and will certainly be unable to do so
without careful observation and intellectual engagement with the problem.
2. In what way(s) is this model an inaccurate way of representing the movement of molecules?



Molecules move continuously.
Marbles can only move in one plane (along the bench); molecules can move in all
planes.
Hitting the bench on either side is not random – it will tend to propel the marbles
together initially.
PRACTICAL How does the cell membrane affect
diffusion? (page 28)
4. Explain the colours that you see inside and outside the visking tubing after 10 minutes.
There will be a blue-black colour inside the visking tubing but not outside. The iodine
molecules have diffused in through the membrane to mix with the starch, but the starch
moleules have been unable to diffuse out.
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WJEC GCSE Additional Science Teacher’s Notes
_ What is osmosis? (pages 29–32)_________________
Questions
3. Here are two answers given in an exam. Neither of them got any marks. What is wrong with each of
these answers?
a ‘In osmosis, water travels in the opposite way from diffusion, that is, from a dilute solution to a
concentrated solution.’
There is more water in a dilute solution than in a concentrated solution, so the direction of
water movement in osmosis is still down a concentration gradient. (It is best to avoid
talking about a high ‘concentration’ of water, as concentrations should be expressed in
terms of the solute, not the solvent.)
b
‘When the concentrations inside and outside a cell are equal, the movement of water stops.’
The movement of water does not stop, it just balances out or ‘reaches an equilibrium’. The
net movement of water stops.
PRACTICAL Osmosis in potatoes (pages 31–32)
1. Describe the trend seen in your results, and explain how it was caused.
As the concentration of sugar increases, the weight increase gets less, and eventually
becomes a weight loss, which then increases. It is important to refer to both the decrease
in weight gain and the increase in weight loss. This is caused initially by the decrease in
the concentration gradient between the solution (high water) and the potato (low water) and
then by the increase in concentration gradient between the potato (high water) and the
solution (low water).
Explaining this is quite a challenge in terms of communication skills and it is
important to know that pupils are expected to provide a full and clear explanation to
gain credit.
2. The experiment can also be done by measuring change in length of the potato cylinders. Explain
why measuring mass is better.
Mass takes account of an increase in all dimensions. It would be possible (though unlikely)
for the cylinder to increase in diameter but not length, which would lead to inaccurate
results.
3. Why was it important to blot the potato cylinders dry before weighing them in step 9?
You don’t want to weigh liquid which is not actually inside the potato. This would lead to
inaccurate results.
4. Why were you asked to record % change in mass and plot that in the graph rather than just change
in mass?
The potato cylinders were identical in size but not necessarily in mass. % increase takes
account of different starting weights.
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WJEC GCSE Additional Science Teacher’s Notes
4
Photosynthesis and
respiration
_How does photosynthesis work? (pages 35–37)______
PRACTICAL Investigating factors needed for
photosynthesis (pages 35–37)
Experiment 2 – Showing the need for chlorophyll
Variegated geranium (green and white) works best for this. Other variegated leaves can be used
but some have thicker cuticles which makes the starch test less successful. This type of
variegated geranium is not always easy to find and it may be advisable to use only a part of a
leaf in each group to allow the plant to survive for later use.
1. Why was there no need to de-starch the leaves used for experiment 2?
This test simply discovers the ‘normal’ situation in a variegated leaf. There is always
chlorophyll in the green parts of the leaf and never in the white parts, so the only thing that
is necessary is to ensure that photosynthesis has had a chance to occur before the
experiment. All the other experiments in this series involve subjecting similar leaves to
varying conditions over a stated time, and so de-starching is necessary because the
experimental conditions only operate over a set time span.
2. In experiment 3, why was leaf A put in a flask containing water?
Leaf A is a control to show that the effect is caused by the absence of carbon dioxide, not by
the experimental treatment. Water is used instead of sodium hydroxide so that humidity
levels will be similar in the two flasks.
Discussion points
Sodium hydroxide is very corrosive. Apart from any safety hazard, what disadvantage could this be in
this experiment? How could this disadvantage be reduced or overcome?
It could be that the sodium hydroxide damages the leaf, and that as a result the leaf does not
photosynthesise. Soda lime could be used as an alternative, with an equal volume of another
solid (e.g. marble chips) used in the control.
_ How can we alter the rate of photosynthesis?_______
(pages 37–39)
TASK What is the effect of increasing light intensity on
the rate of photosynthesis (pages 38–39)
This exercise will stretch more able pupils and will probably be too complex for lower ability
pupils.
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WJEC GCSE Additional Science Teacher’s Notes
1. Why do you think the time taken for 50% of the leaf discs to float was measured in seconds rather
than in minutes and seconds?
It is easier because you don’t have to calculate decimal fractions of a minute. It would be
bad practice to just measure to the nearest minute (inaccurate) or to record minutes and
seconds (mixed units).
2. It was felt that measuring the time taken for 50% of the leaf discs to float would provide a more
accurate measure of photosynthesis than waiting for all the discs to float. Why do you think this is?
If some discs were not viable they may not carry out photosynthesis and so would never
float.
3. Do you think the variation in the results is acceptable to draw a conclusion from? Explain your
answer.
Probably not. Although there is a clear trend, the variation between repeats is often greater
than the difference between the means at adjacent distances.
4. Do you think three repeats for this experiment is enough? Explain your answer.
No. The repeatability of these results is poor and so many more repeats should be done.
5. Do you think that the differences in the results for the different distances are significant? Explain
your answer.
Probably not, given the variation in the results. Even the difference between the results at 30
and 35 cm may not be significant.
6. What conclusion would you draw from these results?
Increasing light intensity may increase the rate of photosynthesis, but further repeats are
necessary in order to say for certain whether this is the case.
NOTE: These are real results which illustrate the uncertainty often found in experimental data.
It should be emphasised that these uncertain results do not mean that light intensity has no
effect on rate of photosynthesis, but simply that the experiment is inconclusive. This is a good
exercise to see if pupils can look at data in an impartial way. They are likely to know that
increasing light intensity should increase rate of photosynthesis, and this may lead them to
exhibit bias when interpreting the results.
_ Why study respiration? (pages 40–41)____________
PRACTICAL How can we measure respiration
(pages 40–41)
1. Explain your results for flask A.
The seeds will be respiring, and respiration produces heat, which is retained by the flask.
2. Explain the purpose of flask B.
Flask B is a control to show that the effect is due to a living process (respiration) in the
seeds.
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WJEC GCSE Additional Science Teacher’s Notes
3. Why were the seeds in flask B rinsed in disinfectant? (Think what is likely to happen to dead seeds.)
To prevent bacteria growing on the seeds (because bacteria would respire).
4. Why were the seeds in flask A not rinsed in disinfectant?
Living seeds will not have very large numbers of bacteria growing on them; there would be
a possibility of the disinfectant damaging the seeds.
5. Although there were roughly the same number of seeds in flask A and flask B, it is not necessary to
have the same number (or the same mass) of beans in each flask. Why not?
We are only comparing whether heat is generated or not, we are not comparing the amount
of heat generated. The number of seeds should be more or less the same, however.
6. Suggest a reason why it would not be a good idea to leave the seeds for much more than 24 hours
before taking the second reading.
If the seeds germinate, the new plants would have no access to light and may die.
_How do organisms survive in places with very little___
oxygen? (pages 42–44)
PRACTICAL How can we measure anaerobic respiration
in yeast? (page 43)
1. Counting bubbles per minute is not a very accurate way to measure carbon dioxide production (and
therefore respiration). Why not?
The bubbles may be difficult to count if they emerge quickly and in clusters, leading to
errors. The bubbles are not identical in size and so number of bubbles is not exactly
equivalent to volume of gas.
2. How could the accuracy be improved?
The easiest way would be to collect the gas over water or in a gas syringe and measure the
volume. Using glass tubing with a wider bore would slow the emergence of the bubbles and
reduce experimental error slightly.
3. From your results, do you think that five repeats were enough? Explain your answer.
The answer will depend on the variation in the results.
4. Design an experiment to test the effect of temperature on anaerobic respiration in yeast. Ensure that
the experiment is fair, and as accurate and repeatable as possible. Include a risk assessment for
your experiment.
Features to look for:
 Control of temperature using water baths.
 Range of at least five temperatures, avoiding very high temperatures which would
certainly denature enzymes and kill the yeast (suggested – no higher than 60 °C).
 Control of:
 concentration of glucose in the solution
 ‘concentration’ of yeast in solution
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WJEC GCSE Additional Science Teacher’s Notes


 volume of yeast and glucose solution
 time period for reading.
Better pupils may suggest controlling pH if they have enough knowledge of enzymes.
This would be relevant as carbon dioxide produced may lower pH.
Risk assessment: the only hazard is the glass tubing, which could break when the bung
is inserted. Precaution – hold bung and not tubing when inserting. Possibility of yeast
allergy is irrelevant as the experiment does not involve ingesting the yeast.
PRACTICAL What effects do respiration and
photosynthesis have on the atmosphere
(pages 43–44)
1. Explain the final colour seen in each tube.
Tube A: Little or no change in colour, because the carbon dioxide produced by respiration
in the snails is absorbed by photosynthesis in the pond weed.
Tube B: Goes red because carbon dioxide is being absorbed by the pond weed during
photosynthesis.
Tube C: Goes yellow because the pond weed is respiring (producing carbon dioxide) but
cannot photosynthesise because of the lack of light.
Tube D: Goes yellow because the snails are respiring (producing carbon dioxide).
Tube E: No change because nothing in it will either use or produce carbon dioxide – it’s a
control.
Note that the balance between respiration and photosynthesis in tube A is not likely to be
perfect, so there may be a slight change in colour.
2. What was the purpose of:
a tube C?
To show that photosynthesis was responsible for colour change in tube B (and therefore,
by implication, in tube A)
b
tube E?
Control tube to show no colour change occurs without snails and pond weed. Also
useful as a colour comparison for tube A.
3. Why were the tubes sealed with cotton wool rather than a cork or bung?
To allow gases in for photosynthesis and/or respiration (particularly in tubes B–D). Will
also avoid build-up of pressure in tubes B–D (though this is unlikely to be a problem).
Questions
1. Explain the trends shown in the graph (Figure 4.13).
Between dawn and dusk, carbon dioxide levels decrease and oxygen levels increase due to
photosynthesis exceeding respiration. Between dusk and dawn the reverse happens because
photosynthesis does not occur due to lack of light, but respiration continues. Look for an
understanding that both photosynthesis and respiration occur in the dawn to dusk
period.
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WJEC GCSE Additional Science Teacher’s Notes
2. The greenhouse contains very few animals. What changes would you expect to see in this graph if
there was a mixed population of animals and plants?
In the dawn to dusk period, there would be less change in the levels of both carbon dioxide and
oxygen. In the dusk to dawn period, the fall in oxygen and rise in carbon dioxide would both
increase.
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WJEC GCSE Additional Science Teacher’s Notes
5
The respiratory system
_How do we breathe? (pages 47–48)_______________
Questions
1. Explain why the balloons inflate when the sheet is pulled down, and deflate when it is pushed up.
The balloons inflate when the sheet is pulled down because that creates more volume/space
around the balloons which results in a lower pressure. The (now) higher pressure inside the
balloons forces them outwards, causing inflation. When the sheet is raised, the process is
reversed, resulting in a higher pressure outside the balloons than inside.
2. List the ways in which this model of the respiratory system is inaccurate.



The lungs are not like balloons – they are more like sponges.
The ‘ribcage’ on the model does not move.
There is more space around the balloons than around the lungs.
3. Do these inaccuracies mean that it is not a useful model of the respiratory mechanism? Explain your
answer.
It is still a useful model because it illustrates how diaphragm movement affects pressure and
then how this alters the shape of the lungs. It is a qualitative model and the inaccuracies would
only affect the scale of the effect.
_How does the air we breathe in differ from that we___
breathe out? (pages 49–50)
Questions
4. Why is the exhaled air warmer than the inhaled air?
The body is warmer than the environment and so it warms the air.
5. Why does exhaled air have more water vapour?
The lining of the alveoli is damp which moistens the air.
6. Explain the change in the percentage of nitrogen in exhaled air (note: the body neither absorbs nor
gives out nitrogen).
The reduction of oxygen and the increase in carbon dioxide roughly balance each other. Water
vapour is added which increases the overall volume. Therefore the percentage of the air that is
nitrogen goes down, even though the actual amount of nitrogen stays the same. (There would
also be a slight decrease in the percentage of other gases, but as the number is so small, the
change is masked when figures are rounded.)
Though demanding, this question is a good test of whether pupils have a full understanding
of percentages.
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WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Demonstrating the difference in carbon
dioxide content of inhaled and exhaled air
(page 50)
1. What are your conclusions from this experiment?
There is more carbon dioxide in exhaled air than in inhaled air.
2. A student put forward a hypothesis that ‘There is carbon dioxide in exhaled air but not in inhaled air’.
a Explain why the evidence from this experiment cannot support this hypothesis.
The test is not sensitive to small amounts of carbon dioxide, so the fact that the ‘inhaled
air’ lime water stays clear does not conclusively prove that there is no carbon dioxide in
inhaled air.
b
Suggest how you could modify the procedure to test this hypothesis.
The lime water should be switched for bicarbonate indicator (pupils may just say ‘a
more sensitive indicator’).
Discussion point
Why does inhaled air come in through tube A and exhaled air go out through tube B?
The tube attached to the mouth in A has its end in air, whereas in B it’s in water. There is
therefore less resistance to air flow in A, so air comes in from tube A. When air is breathed
back into the tubes, it is actually equally easy for the air to travel down either tube, and indeed
some will go back into tube A. However, the effect is more noticeable in B because the air goes
directly into the lime water.
_How does smoking damage the lungs? (pages 51–53)_
Questions
7. Compare the data of a lifelong non-smoker with someone giving up at 30. Roughly how much more
likely is the smoker to develop lung cancer before the age of 65?
About 1% more likely.
8. Suggest a reason why, if you smoke, it is best to give up before the age of 40.
Giving up later than 40 produces less decrease in risk than giving up at 40 or earlier.
Discussion points
Overall, smokers are about 15 times more likely to get lung cancer than non-smokers. In itself, however,
this does not prove that smoking causes lung cancer. Why not, and what extra evidence is needed to show
a causal link?
The point to stress here is that correlation does not prove a causal relationship. The extra evidence
is a mechanism linking smoking and cancer, which has been found. The carcinogens in cigarette
smoke provide clear evidence that smoking is likely to cause cancer.
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WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL What’s in cigarette smoke? (page 53)
1. Suggest a reason for the colour change in the indicator.
Carbon monoxide and carbon dioxide produced by the burning of tobacco are acid gases.
2. Good practice in this experiment is to first suck air through an unlit cigarette for 10 minutes. Suggest
a reason for this.
To ensure that changes are due to tobacco smoke and not atmospheric air (passing through
the tobacco).
3. The colour and smell of the cotton wool shows the presence of tar. It is difficult to measure colour or
smell. Suggest how the procedure could be adjusted so that the amount of tar in two different types
of cigarettes could be compared.
The cotton wool could be weighed before and after the experiment.
_How have attitudes to smoking changed? __________
(pages 53–54)
TASK What are the dangers of passive smoking?
(page 54)
In the report to be written for this section, pupils are asked to consider bias. A common
misunderstanding is that anything reported by a biased website is untrue. Pupils should
understand that bias is often evident in the selection of information reported and ‘skewed’
interpretation of data. Sometimes, however, biased groups can present reliable information.
This is usually when their particular bias aligns with the scientific evidence.
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WJEC GCSE Additional Science Teacher’s Notes
6
Digestion
_Why do we digest food? (pages 56–57)____________
PRACTICAL Using a ‘model gut’ (pages 56–57)
1. Explain what your results show about the gut and digestion.
The results show that starch cannot pass out of the gut into the blood, but glucose can.
Therefore, starch has to be digested into glucose in order for it to be used by the body.
2. Suggest why it is better to use a boiling tube in this experiment, rather than a beaker, which would
hold more water.
The quantity of glucose going into the water from the visking tubing is likely to be small.
The more water there is, the more dilute the glucose solution will be, and if it is too dilute,
the clinistix will not detect it.
Discussion point
How good a model of the gut and blood system do you think this apparatus is? Justify your opinion.
The visking tubing has similar properties to the lining of the gut and so from that point of view
the model is good. Blood is mostly water so using water as a model for blood is reasonable.
However, there are other tissues in the gut between the lining and the blood vessels, and other
substances in the gut and the blood which may affect the process, so the model has some
weaknesses. As the experiment is qualitative rather than quantitative, the model is adequate.
_What food needs digesting? (pages 57–58)_________
Question
1. When people need energy very rapidly (e.g. athletes before strenuous exercise, diabetics with low
blood sugar levels) they take glucose tablets or drinks. Why would glucose be a particularly good
source of rapid energy?
Glucose is high in energy and is already a simple sugar which can pass through the gut wall
without being digested. It would therefore get into the blood quicker than most other
carbohydrates.
PRACTICAL How do we know what our food contains?
(page 58)
1. The more sugar there is in the solution, the further the colour change in the Benedict’s solution
goes. This gives an indication, but not a measure, of how much glucose is in the solution. Suggest
how you might get an actual measure of the amount of glucose in a solution, using the Benedict’s
test.
If you did the test with a series of different concentrations of glucose, and ran it for a set
17
WJEC GCSE Additional Science Teacher’s Notes
time, you could produce a colour chart to show how colour matched the concentration.
2. How accurate do you think your measure (from question 1) would be? Give reasons for your
answer.
Not very accurate. There would be more possible concentrations of glucose solution than
there would be colour changes, and once the colour had gone to brick red any further
increase in concentration would not be detectable.
_ Where in the body is food digested? (pages 59–60)__
Question
2. As well as digesting proteins, the stomach also contains acid, which kills off bacteria present in the
food. Why do you think this acid is best placed in the stomach rather than in
a the small intestine
It is better to kill the bacteria as soon as possible. The food enters the stomach before it
enters the small intestine.
b
the mouth
Various answers are possible:
 The food does not stay in the mouth for very long.
 The acid would affect the taste of food.
 The acid could rot the teeth.
_What does bile do? (pages 61–62)________________
PRACTICAL What are the optimum conditions for lipase
enzymes? (pages 61–62)
1. What effect did temperature have on the enzyme activity?
Activity should increase as temperature rises, until the point of denaturation. Denaturation
may not be observed, however.
2. What effect did the liquid detergent have on enzyme activity?
The detergent should increase the enzyme activity (but pupils must interpret the data they
obtain, whatever it shows).
3. Looking at the results, do you think they were accurate? Give a reason for your answer.
The judgement here will depend on the data obtained.
4. Suggest one possible source of inaccuracy in this experiment.
The main source of inaccuracy is the difficulty in judging the exact point at which the
indicator changes from pink to colourless. There may be some temperature fluctuation in the
non-electronic water baths.
18
WJEC GCSE Additional Science Teacher’s Notes
7
Biodiversity and the
environment
_How can biodiversity be maintained? (pages 65–66)__
Questions
1. Suggest a possible reason for the decline in woodland birds since 1970.
 Loss of habitat (tree felling)
 Decrease in prey populations
 Increase in predator populations
 Disease
Loss of habitat is a more likely explanation than the others.
2. Suggest a possible reason for the decline in farmland birds since 1970.
As for Question 1. However, habitat loss is a less likely cause (though there has been some loss
on farmland), and decline in prey populations is a more likely cause, as much of their prey
would be insect pests which have been reduced by farmland management.
3. The graphs go up to 2008. What do you think would happen to the populations of the different types of
bird if further data had been published for 2010? Explain your answer.
Seabirds and water and wetland bird populations look roughly stable. Woodland birds have an
upturn in 2008 which might continue. Farmland birds seem to be in slow decline but the 2008
figure suggests this may be levelling off.
Note that for all three questions, definite answers cannot be given. Teachers should assess on the
basis of communication skills and the thought given to the answers. Answers should be reasonable,
and would be better if justified (Question 3 requires justification).
Discussion point
Suggest how the data in the graph might help to find reasons for the decline in woodland and farmland
birds.
There is no direct evidence in the graph for reasons for the decline. However, the graph does
provide some useful clues:
 Significant decline in farmland birds started around 1980 and woodland birds around 1990. It
would be useful to look for any changes that took place in those habitats at those times.
 The clear divergence in the different populations indicates that the cause is linked to the
habitat, it is not just something happening to birds in general.
_How can we get data about biodiversity in an_______
environment? (pages 67–68)
Questions
4. Scientists sampled an area of 1000 m2 on a beach that had an area of 1 km2 (1 000 000 m2). They
found 293 cockles. Estimate how many cockles there were on the whole beach.
19
WJEC GCSE Additional Science Teacher’s Notes
The sampled area represents 1000/1 000 000 (1/1000) of the whole beach. Therefore, the
number of cockles on the whole beach will be 293 x 1000 = 293 000
5. Look at the environments in Figure 7.5. Suggest a reason why scientists would need to use a bigger
sample area in woodland than in the saltmarsh.
The saltmarsh is a much more homogenous habitat. A sample taken from anywhere is likely to
be similar to any other area. In the woodland there is much more diversity within the habitat
and samples from (e.g.) open areas may be significantly different from those in the midst of
tree cover.
PRACTICAL Counting daisies (page 68)
Suggest any possible disadvantages of the method used to place the quadrat randomly.
It is not really random. It is perfectly possible to look behind you and there is a choice of place
to stand. A better method would be to divide the area into a marked grid of squares, with each
square the size of the quadrat used. Allocate each square a number and use a random number
generator to decide which squares to sample. Throwing over the shoulder is less scientifically
random but much quicker and easier to do.
_How can we find out about the distribution of_______
organisms? (pages 68–70)
PRACTICAL What effect does trampling have on plants?
(page 70)
For Questions 1, 2 and 4 the answers will depend upon results obtained.
For Question 3 the answer will depend upon the site chosen, but light intensity is a likely factor.
_How can we measure an animal population that moves
around? (pages 71–72)
Question
6. Dave wanted to estimate the population of woodlice in his garden. He searched around and collected
100 woodlice. He marked each of them with a spot of white paint on its back, and released them (see
Figure 7.10). A week later he went into his garden and collected another 100 woodlice. Four of those
were marked ones that he had captured before. Using the equation given earlier in this section,
calculate the size of the woodlouse population in Dave’s garden.
N
100  100 10000

 2500 woodlice
4
4
Discussion point
How good do you think Dave’s experimental method was? Could he have improved it in any way?

White paint is quite bright and could make the marked woodlice more noticeable to predators,
and more likely to be found when he took his second sample. A darker colour would have been
better.
20
WJEC GCSE Additional Science Teacher’s Notes

He could have left them for longer than a week or taken larger samples, but one week and a
sample of 100 are reasonable.
Overall the method is adequate, the only weakness being the colour of the paint.
_Why can introducing new species to an area cause
problems? (pages 72–74)
TASK What are the advantages and disadvantage of
biological control? (page 74)
On the internet, research the pros and cons of biological control, and some of the different methods
used. Write a report on your findings.
The criteria used for the controlled assessment research task could be applied here. In
Additional Science, research and communication skills are assessed in a less specific way
throughout the controlled assessment.
21
WJEC GCSE Additional Science Teacher’s Notes
8
Atomic structure and the
Periodic Table
_What is the structure of an atom? (pages 75–78)____
Questions
1. Look at the information about the sodium atom. How many protons, neutrons and electrons are there in
the atom?
11 protons, 12 neutrons, 11 electrons.
2. Using the information in Table 8.4, draw the atoms of:
a carbon
b
hydrogen
2,4
c
1
d
silicon
potassium.
2,8,4
2,8,8,1
3. Which element’s atom is shown in this diagram (Figure 8.4)?
Nitrogen
4. Look at the first 20 elements, and which group they are in. What is the connection between the group
number and the electron configuration? (Note: Hydrogen is not in a group.)
The number of the group is the number of electrons in the outer shell of the element.
5. For the first 20 elements, what is the relationship between the period the element is in and its electron
configuration?
The period is the same as the number of electron shells in the atom.
22
WJEC GCSE Additional Science Teacher’s Notes
_ How heavy is an atom? (pages 79–80)____________
Questions
6. Find the relative molecular masses of:
a
ammonia, NH3
14 + (3 x 1) = 17
b
methane, CH4
12 + (4 x 1) = 16
c
hydrogen sulfide, H2S
(2 x 1) + 32 = 34
7. Find the relative formula masses of:
a
calcium chloride, CaCl2
40 + (2 x 35.5) = 111
b
copper(II) oxide, CuO
64 + 16 = 80
23
WJEC GCSE Additional Science Teacher’s Notes
9
Alkali metals and halogens
_The alkali metals (pages 83–91)__________________
PRACTICAL Observing patterns of reactivity – the alkali
metals (pages 87–89)
Safety: take care with these demonstrations and ensure that you consult the relevant CLEAPSS
guidance.
1. Which alkali metal reacts most vigorously with:
a
air?
Potassium
b
water?
Potassium
c
chlorine?
Potassium
2. Using your observations, arrange the three alkali metals in order of their reactivity (from least to
most reactive).
Lithium then sodium then potassium
3. Using a Periodic Table, arrange all the Group 1 metals in order of reactivity.
Lithium, sodium, potassium, rubidium, caesium, francium
4. How does reactivity vary as you move down Group 1 of the Periodic Table?
The elements get more reactive as you move down the Group.
5. Look again at the electronic structure of the alkali metals in Table 9.1. Is there a pattern between the
electron structure and the reactivity of the alkali metals? Can you explain this pattern?
Alkali metals all have a single electron in their outer shell. The further down the group, the
weaker this single electron is held to the atom (there are more electron shells beneath it).
The weaker the electron is held, the more reactive the metal.
6. Predict the observations that you mighht make from the reactions of rubidium with oxygen (in air),
water and chlorine.
Rubidium will react much more violently with all three reactants, exploding on contact (see
Discussion Point).
7. Why are the reactions of potassium with chlorine, and any of the other alkali metals with any of the
other chemicals, not allowed to be carried out in schools?
The reactions are far too violent to be carried out using normal school facilities.
8. Use the word and balanced symbol equations for lithium to produce similar word and balanced
symbol equations for the reactions of sodium and potassium with oxygen, water and chlorine.
24
WJEC GCSE Additional Science Teacher’s Notes
sodium + oxygen → sodium oxide
4Na(s) + O2(g) → 2Na2O(s)
sodium + water → sodium hydroxide + hydrogen
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
sodium + chlorine → sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
potassium + oxygen → potassium oxide
4K(s) + O2(g) → 2K2O(s)
potassium + water → potassium hydroxide + hydrogen
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
potassium + chlorine → potassium chloride
2K(s) + Cl2(g) → 2KCl(s)
9. Bromine is a halogen like chlorine but it is less reactive than chlorine gas. Predict the reactions of
bromine with lithium, sodium and potassium.
Lithium burns readily in bromine, as do sodium and potassium, the reactions becoming
more violent from sodium to potassium.
10. Write word and balanced symbol equations for the reactions of bromine with lithium, sodium and
potassium.
lithium + bromine → lithium bromide
2Li(s) + Br2(g) → 2LiBr(s)
sodium + bromine → sodium bromide
2Na(s) + Br2(g) → 2NaBr(s)
potassium + bromine → potassium bromide
2K(s) + Br2(g) → 2KBr(s)
Discussion point
Rubidium and caesium react far too violently with oxygen, water and chlorine to be performed even by
demonstration in schools. You can, however, see video clips online of these reactions occuring under
very special controlled conditions. The best example of this is Brainiac: Science Abuse!
www.youtube.com/watch?v=eCkolYB_8co
Show the YouTube clip in conjunction with Question 6 above.
PRACTICAL Flame tests of alkali metal salts
(pages 90–91)
Safety – take care with these practicals and ensure that you consult the relevant CLEAPSS
guidance.
1. Were there any differences in the colours of the different alkali metal salts using the three different
methods?
The flame colours will be very similar with each method.
25
WJEC GCSE Additional Science Teacher’s Notes
2. What were the patterns in the colours produced by:
a
lithium salts?
burn with a crimson (carmine) red colour
b
sodium salts?
burn with an orangy-yellow colour
c
potassium salts?
potassium salts burn with a lilac colour
3. Which method do you think produced the best results? Explain your answer.
Student choice.
4. Explain how you could use this technique to identify any metal ion components of an unknown salt –
for example, if a white powder was found at the scene of a crime, how could a flame test help to
identify the white powder?
Since many metal ions burn with characteristic ‘fingerprint’ colours, the colour of the flame
of the unknown white powder could identify the metal ion in the white powder.
_Halogen reactions (pages 92–97)_________________
PRACTICAL Observing the reaction of halogens with iron
(pages 93–94)
Safety – take care with these practicals and ensure that you consult the relevant CLEAPSS
guidance.
1. Which halogen reacted most vigourously with the iron wool?
Chlorine
2. Arrange the three halogens in order of reactivity, from most reactive to least reactive.
Chlorine then bromine then iodine
3. How does halogen reactivity vary as you go down Group 7?
Halogen reactivity decreases down the Group.
4. Where would fluorine and astatine be on your halogen reactivity series?
Fluorine would be above chlorine and astatine would be below iodine.
5. Write word and balanced symbol equations for the reactions of chlorine, bromine and iodine with
iron.
iron + chlorine → iron(III) chloride
2Fe(s) + 3Cl2(g) → 2FeCl3(s)
iron + bromine → iron(III) bromide
2Fe(s) + 3Br2(g) → 2FeBr3(s)
iron + iodine → iron(III) iodide
2Fe(s) + 3I2(g) → 2FeI3(s)
26
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Halogen displacement reactions
(pages 94–95)
Safety – take care with these practicals and ensure that you consult the relevant CLEAPSS
guidance.
1. Will chlorine displace bromine from solutions of metal bromide and iodine from metal iodies?
Yes
2. Does reactivity increase or decrease as you go up Group 7 of the Periodic Table? How do the
results and observations of the halogen displacement reactions back this up?
Reactivity increases up the group. Chlorine displaces bromine and iodine; bromine will
only displace iodine; iodine will not displace either.
3. Write word and balanced symbol equations for the displacement of bromine by chlorine from
solutions of:
a
sodium bromide
chlorine + sodium bromide → bromine + sodium chloride
Cl2(g) + 2NaBr(aq) → Br2(l) + 2NaCl(aq)
b
potassium bromide
chlorine + potassium bromide → bromine + potassium chloride
Cl2(g) + 2KBr(aq) → Br2(l) + 2KCl(aq)
4. Write word and balanced symbol equations for the displacement of iodine by chlorine and then by
bromine from solutions of:
a
sodium iodide
chlorine + sodium iodide → iodine + sodium chloride
Cl2(g) + 2NaI(aq) → I2(l) + 2NaCl(aq)
bromine + sodium iodide → iodine + sodium bromide
Br2(g) + 2NaI(aq) → I2(l) + 2NaBr(aq)
b
potassium iodide
chlorine + potassium iodide → iodine + potassium chloride
Cl2(g) + 2KI(aq) → I2(l) + 2KCl(aq)
bromine + potassium iodide → iodine + potassium bromide
Br2(g) + 2KI(aq) → I2(l) + 2KBr(aq)
5. What would be the reaction between astatine and sodium fluoride?
There would be no reaction.
6. Describe the reaction between fluorine with potassium iodide. What observations would you make?
Write word and balanced symbol equations for this reaction.
A dark brown discoloration of iodine would start to form as fluorine gas was bubbled
through potassium iodide.
fluorine + potassium iodide → iodine + potassium fluoride
F2(g) + 2KI(aq) → I2(l) + 2KF(aq)
27
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL The tests for halides (page 96)
Safety – take care with these practicals and ensure that you consult the relevant CLEAPSS
guidance.
Silver nitrate is quite expensive, encourage students to use sparingly.
1. What is the test for a chloride?
A white precipitate (that turns darker in sunlight) of silver chloride is formed when silver
nitrate is added to a chloride salt.
2. How are the tests for bromides and iodides different from chlorides?
Bromides produce pale yellow precipitates of silver bromide that are insoluble in dilute
ammonia solution, but soluble in concentrated ammonia solution. Iodides produce yellow
precipitates of silver iodide that are insoluble in ammonia solution.
3. When is it important to add nitric acid to the test?
Nitric acid should be added when the test chemical is an unknown to prevent other ions such
as carbonate and hydroxide interfering with the silver nitrate reaction.
4. Write balanced ionic symbol equations for the bromide test and the iodide test.
Ag+(aq) + Br-(aq) → AgBr(s)
Ag+(aq) + I–(aq) → AgI(s)
5. You are presented with a white solid powder. You suspect that the powder could be either
potassium iodide or sodium chloride. Explain the chemical tests that you would perform and the
order that you would perform them, to confirm the identity of the unknown white powder.
First perform flame test to identify the metal ion:
lilac flame = potassium; orangey-yellow flame = sodium.
Then confirm the non-metal ion using the halide test with silver nitrate:
white precipitate = chloride; yellow precipitate = iodide.
PRACTICAL What’s the powder? (page 97)
Safety – take care with these practicals and ensure that you consult the relevant CLEAPSS
guidance.
Silver nitrate is quite expensive, encourage students to use sparingly.
This practical could be extended significantly by giving students a range of common alkali
metal halides and asking them to identify all the salts (Labelled A, B, C, etc). Ensure that you or
your technician makes a note of which salt is labelled with which letter!
28
WJEC GCSE Additional Science Teacher’s Notes
10
Chemical bonding, structure
and properties
_Copper – a metal (pages 99–100)_________________
Questions
1. What are the two most important properties of metals?
Metals are good conductors of heat and electricity.
2. What properties make copper such a good material for making water pipes?
Copper is unreactive, malleable and ductile.
3. Why are electrical connecting wires made out of strands of copper?
Strands of wire allow the connecting leads to be much more flexible.
4. Why are metals such good conductors of electricity?
Metals have a ‘sea’ of negatively charged, free electrons that can easily move throughout the
structure of the metal.
5. Describe how the ‘positive ion/free electron’ model of copper can be used to explain its physical
properties:
a High melting and boiling point
The metallic bonds holding the positive metal ions together in their lattice structure are
very strong and need a lot of heat energy to break them.
b
Ductility
Although metallic bonds are strong, copper has relatively weaker bonds than other metals
making it quite ductile – the bonds can be pulled apart during stretching.
c
Malleability
As (b) but the bonds can also be hammered or squashed into shape.
d
Toughness
The fact that the copper metallic bonds allow themselves to be deformed out of shape
means that they will not fracture (break apart) easily when stressed.
Discussion point
Your teacher may show you an animation of conduction of electricity in a metal. How does the conductivity
of a metal change with temperature, the dimensions of the wire and the material that the wire is made of?
An excellent animation to use, if you can get hold of a copy of it, is ‘Resistance Simulator’ by
Vibrant Effects Ltd.
On-line alternatives are:
www.absorblearning.com/media/item.action?quick=t6
www.absorblearning.com/media/item.action?quick=11a
29
WJEC GCSE Additional Science Teacher’s Notes
_ Sodium chloride (common salt) – an ionic compound _
(pages 100–102)
Questions
6. How are sodium and chloride ions formed from sodium and chlorine atoms?
Sodium ions form from sodium atoms when the outermost electron on the sodium atom is
removed. Chloride ions form from chlorine atoms when an extra electron is added to its
electron configuration.
7. Why is sodium chloride (common salt) used as a flavouring and preservative for food?
Our tongues have evolved to sense the flavour of common salt ‘saltiness’ (along with
bitterness, sweetness and sourness). Common salt is used as a food preservative, particularly
with meat or fish, because it draws the water moisture out of the food (and the microorganisms that cause the meat to go rotten) allowing the food to be edible for a longer period.
8. Explain why sodium chloride crystals are brittle.
Sodium chloride crystals are brittle because when a stress is applied across the crystal the ion
layers will shift causing a fracture.
9. What happens when sodium chloride crystals are added to water?
When added to water, the sodium chloride crystal lattice breaks down (dissolves) and a
solution of positive sodium ions and negative chloride ions is formed.
10. Molten and solid sodium chloride contain the same sodium and chloride ions. Why does molten sodium
chloride conduct electricity, while solid sodium chloride does not conduct electricity.
In solid sodium chloride the ions are not free to move, yet in molten sodium chloride they are
free to move (and create an electric current).
11. Calcium oxide is another ionic compound. Calcium has two electrons in its outer shell, and oxygen has
six electrons in its outer shell. Draw dot and cross diagrams to show how calcium oxide is formed by
electron transfer from calcium to oxygen atoms.
calcium ion, Ca2+, 2,8,8
oxygen ion, O2–, 2,8
12. Draw dot and cross diagrams to show the formation of:
a
Lithium fluoride from
lithium and fluorine
lithium ion, Li+, 2,8
fluoride ion, F–, 2,8
30
WJEC GCSE Additional Science Teacher’s Notes
b
Sodium sulfide from sodium and sulfur
c
Magnesium chloride from magnesium and chlorine.
Discussion point
Salt is incredibly important to us as human beings. Find out why our bodies rely on salt so much and why it
is important to regulate the amount of salt that we consume in our food.
A good place to start to search about this topic is:
www.rsc.org/Chemsoc/Chembytes/HotTopics/Salt/whysalt.asp
_ Water – a simple covalent molecule (pages 103–104)_
Questions
13. What is a convalent bond?
A covalent bond is formed where two or more atoms share electrons in their electron
configurations.
31
WJEC GCSE Additional Science Teacher’s Notes
14. How is water formed from hydrogen and oxygen?
The oxygen atom shares one electron from one hydrogen atom and another electron from a
second hydrogen atom.
15. Why is water a liquid at room temperature?
The freezing point of pure water is 0 °C and its boiling point is 100 °C, room temperature
(10–20 °C) is between these two values hence water is a liquid at these temperatures.
16. Why is water only a poor conductor of electricity?
There are few H+ and OH– ions in pure water – hence there are few charged particles free to
move and so water is a poor conductor of electricity.
17. Draw dot and cross diagrams showing the covalent bonds in the following molecules:
a
hydrogen chloride
b
ammonia
c
methane
18. Some atoms can form double covalent bonds. In these molecules, each atom shares four electrons (in
two pairs). Carbon dioxide is an example of a molecule containing double covalent bonds.
Draw dot and cross diagrams and structural formulae for the following molecules containing double
covalent bonds:
a
sulfur dioxide
b
oxygen gas
32
WJEC GCSE Additional Science Teacher’s Notes
Discussion point
Water is an unusual molecule in many ways. Find out some of the properties of water that make it different
from other simple molecular compounds. For example, why does water conduct electricity at all, and why
does ice float?
There are many places on the net to find answers to these questions. This would make an excellent
homework task.
The USGS has a good webpage with some of water’s basic properties:
http://ga.water.usgs.gov/edu/waterproperties.html
_Diamond and graphite – giant covalent substances
(pages 104–106)
Questions
19. What is an allotrope?
Allotropes are different physical forms of the same element. The atoms are the same, but they
are arranged in different configurations.
20. How are the structures of graphite and diamond different?
In diamond, each carbon atom is bonded to four other carbon atoms with a strong covalent
bond in a tetrahedral shape. In graphite, one of the bonds is very weak and the structure is
arranged in strong hexagonal layers with the weak bond holding the layers together.
21. Why do both graphite and diamond have very high melting points?
The covalent bonds between the atoms are very strong so they have very high melting points.
22. Why is diamond hard, yet graphite is soft?
The weak bonds between the layers of carbon atoms on graphite makes graphite quite soft, the
tetrahedral bonding of the carbon atoms in diamond makes diamond very strong.
23. Explain why graphite is a non-metal, yet it conducts electricity.
The weakly bound shared electron between the layers of carbon atoms in graphite can move
quite easily along the layers making graphite a ‘semi-conductor’ along these layers.
Discussion point
Allotropes can be found in other elements as well. Find out about the different allotrope forms of:




phosphorous
oxygen
sulfur
tin
Phosphorus allotropes: white, black, red and violet.
Oxygen allotropes: atomic (single), molecular dioxygen (double), ozone (triple), tetraoxygen
(quadruple) and solid (six different physical forms known).
Sulfur allotropes: there are many different allotropes of sulfur including the most common S8 form.
Tin allotropes: there are four known allotropes of tin, including the two most common forms, grey
tin and white tin.
33
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Making molecular models (page 106)
A unit cell is the smallest repeating unit in the structure of a giant structure.
sodium chloride
unit cell
diamond
unit cell
graphite unit cell
_ Carbon nanotubes (pages 106–107)______________
Questions
24. What are carbon nanotubes?
Carbon nanotubes are another allotrope of carbon produced when graphite layers form and then
roll up into tubes rather than being deposited in layers.
25. Why are materials made from carbon nanotubes a good choice for components on a bike?
Carbon nanotubes are incredibly strong, but very lightweight. This makes them ideal for use on
high performance bicycle components.
26. Why do carbon nanotubes conduct electricity? How could they be made into electrical connections
inside electronic devices?
Carbon nanotubes are good conductors of electricity due to the free electrons that can move up
and down the tubes. The tubes could be manufactured to behave like electrical wire
connections between electronic components on printed circuit boards – with very high
conductivities yet 10 000 times thinner than a human hair!
Discussion point
Carbon nanotubes are definitely a material for the future – can you think of any good applications for a very
lightweight, incredibly strong, electrically conducting material?
Lots of military applications, portable computing, mobile phones, aerospace engineering, etc.
_Smart materials (pages 108–109)________________
Questions
27. What is a ‘smart material’?
Smart materials have properties which change reversibly with a change in their surroundings.
28. Explain the difference between:
a
a thermochromic pigment and a photochromic pigment
A thermochromic pigment changes colour with changing temperature, whereas a
photochromic pigment changes colour with changing light intensity.
34
WJEC GCSE Additional Science Teacher’s Notes
b
a shape-memory polymer and a shape-memory alloy
Shape memory materials return to their original shape once deformed when heated. Shapememory polymers are made of ‘plastic’ materials whereas shape-memory alloys are metals.
29. How can hydrogels be made to absorb more or less water?
By changing their temperature or pH.
30. Explain why smart materials are used to manufacture:
a
photochromic flexi glasses
Photochromic flexi glasses – can be bent out of shape yet returned to their original shape
and get darker as the intensity of the sunlight increases.
b
sport gum-shields
Sport gum-shields – can be heated to allow them to be fitted snuggly to the teeth, and then
cooled to retain the shape. If the gum-shield needs to be re-fitted it can simply be heated
up, returned to its original shape and then re-fitted to the teeth.
c
battery power indicators
Battery power indicators – a thermochromic pigment can be mixed with a conducting
substrate and ‘painted’ onto the side of a battery. When fingers complete the circuit a small
current flows through the conducting substrate which heats up the thermochromic paint
causing it to change colour – more current, more heat, different colours.
d
novelty T-shirts
T-shirts that change colour due to changes in body or surrounding temperature or changes
in the ambient light intensity.
35
WJEC GCSE Additional Science Teacher’s Notes
11
Rates of reaction and
chemical calculations
_Measuring the rate of a reaction (pages 111–15)_____
PRACTICAL Measuring rates of reaction (pages 112–15)
Safety: make sure you consult the relevant CLEAPSS guidance before conducting this practical
work.
Measuring reactions involving gases
1. What is the shape of your graph?
The graph will be a positive curve with a decreasing positive gradient.
2. What does your graph tell you? Where is the rate of reaction fastest?
The rate of reaction is highest at the start of the reaction and it gradually decreases with
time.
3. Can you tell when the reaction is complete?
The reaction is complete when the volume of gas produced stays constant for a period of
time.
4. Calculate the rate of reaction at the steepest part of your graph by drawing a tangent line and
measuring the gradient (the units will be cm3/s).
Student measurements from their own graph.
5. Repeat the rate of reaction calculations for both methods. Are the rates of reaction the same?
Should they be the same? Why might the two rates be different?
The rates of reaction are likely to be similar – they should be the same, but there may be
differences due to more or less ambient air in the tubes, friction in the gas syringe, leaks,
etc.
Measuring reactions involving changes of mass
6. What is the shape of your graph?
The graph will be a negative curve with decreasing negative gradient.
7. What does your graph tell you? Where is the rate of reaction fastest?
The rate of reaction is highest at the start of the reaction and it gradually decreases with
time.
8. Can you tell when the reaction is complete?
The reaction is complete when the mass of the system stays stays constant for a period of
time.
36
WJEC GCSE Additional Science Teacher’s Notes
9. Calculate the rate of reaction at the steepest part of your graph by drawing a tangent line and
measuring the gradient (the units will be g/s).
Student measurements from their own graph.
Measuring reactions involving changes of ligh transmission through a
precipitate
10. What is the pattern/shape of your graph?
The graph will be a negative curve with decreasing negative gradient.
11. What does your graph tell you? Where is the rate of reaction fastest?
The rate of reaction is highest at the start of the reaction and it gradually decreases with
time.
12. Can you tell when the reaction is complete?
The reaction is complete when the light transmission of the system stays constant for a
period of time.
Questions
1. What is meant by the rate of a reaction?
How much reaction product is produced in a set time.
2. Explain how you use a graph to measure the rate of a reaction.
Draw a tangent line to the reaction curve at any point in time – the rate of reaction is the
gradient (slope) of the line.
3. How can you tell from a rate of reaction graph where the reaction is:
a
fastest?
The rate of reaction is fastest where the gradient is biggest (where the slope is steepest).
b
complete?
The reaction is complete where the graph is horizontal, when the gradient is zero.
4. In a calcium carbonate and hydrochloric acid experiment, a student collects the carbon dioxide gas and
produces the rate of reaction graph shown in Figure 11.10. On a copy of this graph, sketch the graph
you would expect from similar experiments carried out with:
a
acid of twice the concentration, but at the same temperature
The rate of reaction will be the same, as this is limited by the concentration of the acid not
the amount.
b
the same amount of each chemical, but carried out at a higher temperature.
A higher temperature means a faster rate of reaction, but as the amount of chemicals is
fixed, the final volume of gas will be the same.
37
WJEC GCSE Additional Science Teacher’s Notes
_ The importance of catalysts? (pages 117–120)______
Questions
5. What is a catalyst?
Catalysts are substances that increase the rate of a chemical reaction but remain chemically
unchanged at the end of the reaction.
6. How can the rate of reaction of calcium carbonate with hydrochloric acid be increased?




Increase the surface area of the calcium carbonate (powder)
Increase the concentration of the hydrochloric acid
Increase the temperature of the reaction
Use a suitable catalyst
7. When magnesium reacts with hydrochloric acid, hydrogen gas is produced. In a particular experiment
at 20 °C, 50 cm3 of hydrogen gas was produced in 3 minutes. What would be the result of the reaction if
the same quantities of reactant were used but the reaction was carried out at 30 °C?
The same amount of hydrogen gas would be produced (50 cm3) but the rate of reaction would
be faster – it would produce the same amount of gas in less time.
8. Why is it important to a chemical company to increase the yield of a reaction?
Increasing the yield of a reaction creates more profit – the company can make and sell more
product for the same amount of reactants.
9. Why is it important for the environment to use catalysts in the production of chemicals?
Catalysts reduce the amount of energy required to produce chemical products which in turn
preserves world fuel reserves and also reduces the environmental impact of burning fossil fuels
and its effect on the greenhouse effect and global warming.
Discussion point
The Haber Process is incredibly important to the whole of the world’s population. Not only is a catalyst used
for the reaction between nitrogen and hydrogen, but the process is optimised by adjusting the temperature
and pressure of the reaction.
Your teacher will show you an animation of the process where you can adjust the temperature and pressure
of the reaction. Find out the conditions to produce the optimum yield.
www.freezeray.com/flashFiles/theHaberProcess.htm
Use the instructions given on the website above, or use another suitable animation. Generally, the
pressure of the reaction is about 200 atm and the temperature is about 450 °C.
TASK Simulating rates of reaction (page 119)
There are many different commercial and web-based rate of reaction simulators available. The
one shown in Figure 11.15 is particularly user-friendly and can be obtained via:
www.focuseducational.com/product/science-investigations-1/40
This task would be best carried out individually on a school computer network where there is
direct access to Excel.
38
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Investigating the rate of a reaction
(pages 119–120)
Give students a suitable range of reactions to investigate – you could have different groups
doing different reactions and different factors then pooling the results. This Practical (and its
report outcome) has been deliberately left open to suit local conditions and time constraints.
_Chemical calculations (pages 120–29)_____________
Questions
10. Calculate the relative molecular mass, Mr, for the following molecules.
a
oxygen gas, O2
= [16 + 16] = 32
b
sulfur dioxide, SO2
= [32 + (2 × 16)] = 64
c
methane, CH4
= [12 + (4 × 1)] = 16
d
nitrogen dioxide, NO2
= [14 + (2 × 16)] = 46
e
carbon tetrachloride, CCl4
= [12 + (4 × 35.5)] = 154
f
ammonia, NH3
= [14 + (3 × 1)] = 17
g
ethane, C2H6
= [(2 × 12) + (6 × 1)] = 30
11. Calculate the relative formular mass of the following ionic compounds.
a
lithium chloride, LiCl
= [7 + 35.5] = 42.5
b
potassium oxide, K2O
= [(2 × 39) + 16] = 94
c
sodium sulfide, Na2S
= [(2 × 23) + 32] = 78
d
magnesium carbonate, MgCO3 = [24 + 12 + (3 × 16)] = 84
e
calcium nitrate, Ca(NO3)2
= [40 + (2 × (14 + (3 × 16)))] = 164
f
beryllium oxide, BeO
= [9 + 16] = 25
g
rubidium carbonate, Rb2CO3
= [(2 × 85) + 12 + (3 × 16)] = 230
h
ammonium sulfate, (NH4)2SO4
= [(2 × (14 + (4 × 1))) + 32 + (4 × 16)] = 132
12. Calculate the percentage composition of each molecule or compound in Questions 10 and 11.
Molecules in Question 10:
a
oxygen gas, O2
100 % oxygen
b
sulfur dioxide, SO2
50 % sulfur, 50 % oxygen
c
methane, CH4
75 % carbon, 25 % hydrogen
d
nitrogen dioxide, NO2
30.4 % nitrogen, 69.6 % oxygen
e
carbon tetrachloride, CCl4
7.8 % carbon, 92.2 % chlorine
f
ammonia, NH3
82.4 % nitrogen, 17.6 % hydrogen
g
ethane, C2H6
80 % carbon, 20 % hydrogen
39
WJEC GCSE Additional Science Teacher’s Notes
Ionic compounds in Question 11:
a
lithium chloride, LiCl
16.5 % lithium, 83.5 % chlorine
b
potassium oxide, K2O
83 % potassium, 17 % oxygen
c
sodium sulfide, Na2S
59 % sodium, 41 % sulfur
d
magnesium carbonate, MgCO3 28.6 % magnesium, 14.3 % carbon, 57.1 % oxygen
e
calcium nitrate, Ca(NO3)2
24.4 % calcium, 17.1 % nitrogen, 58.5 % oxygen
f
beryllium oxide, BeO
36 % beryllium, 64 % oxygen
g
rubidium carbonate, Rb2CO3
73.9 % rubidium, 5.2 % carbon, 20.9 % oxygen
h
ammonium sulfate, (NH4)2SO4
21.2 % nitrogen, 6.1 % hydrogen, 24.2% sulfur, 48.5 %
oxygen
13. Calculate the total mass of reactants and products in the following reactions:
a
N2 (g) + 3H2 (g) → 2NH3 (g)
Reactants: (2 × 14) + 3 × (2 × 1) = 34
Products: 2 × (14 + (3 × 1)) = 34
b
2H2 (g) + O2 (g) → 2H2O (g)
Reactants: 2 × (2 × 1) + (2 × 16) = 36
Products: 2 × ((2 × 1) + 16) = 36
c
Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2O (g)
Reactants: 24 + ((2 × 1) + 32 + (4 × 16)) = 122
Products: (24 + 32 + (4 × 16)) + (2 × 1) = 122
d
NaOH (aq) + HNO3 (aq) → NaNO3 (aq) + H2 (l)
Reactants: (23 + 16 + 1) + (1 + 14 + (3 × 16)) = 103
Products: (23 + 14 + (3 × 16) + ((2 × 1) +16) = 103
14. Calculate the mass of calcium oxide formed by the complete decomposition of 5 kg of calcium
carbonate.
CaCO3 (s) → CaO (s) + CO2 (g)
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100
Relative formula mass of calcium oxide = 40 + 16 = 56
So 100 g of calcium carbonate makes 56 g of calcium oxide
1 g of calcium carbonate makes (56/100) = 0.56 g of calcium oxide
5 kg = 5000 g of calcium carbonate makes 5000 × 0.56 = 2800 g of calcium oxide = 2.8 kg
15. Calculate the mass of sodium chloride that can be formed from the neutralisation of 8 kg of sodium
hydroxide with hydrochloric acid.
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
Relative formula mass of sodium hydroxide = 23 + 16 + 1 = 40
Relative formula mass of sodium chloride = 23 + 35 = 58
So 40 g of sodium hydroxide makes 58 g of sodium chloride
1 g of sodium hydroxide makes (58/40) = 1.45 g of sodium chloride
8 g of sodium hydroxide makes 8 x 1.45 = 11.6 g of sodium chloride
40
WJEC GCSE Additional Science Teacher’s Notes
16. Calculate the mass of calcium chloride that can be formed by the reaction of 3 g of calcium cabonate
with an excess of hydrochloric acid.
CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100
Relative formula mass of calcium chloride = 40 + (2 × 35) = 110
So 100 g of calcium carbonate makes 110 g of calcium chloride
1 g of calcium carbonate makes (110/100) = 1.1 g of calcium chloride
3 g of calcium carbonate makes 3 × 1.1 = 3.3 g of calcium chloride
PRACTICAL Calculating the formula of copper(II) oxide
(pages 124–25)
Safety: make sure you consult the relevant CLEAPSS guidance before conducting this practical
work.
Answers to Questions 1–5 will depend on the Students’ results. The ratio should be
approximately 1:1.
PRACTICAL Calculating the formula of magnesium oxide
(pages 125–26)
Safety: make sure you consult the relevant CLEAPSS guidance before conducting this practical
work.
Answers to Questions 1–5 will depend on the Students’ results. The ratio should be
approximately 1:1.
Questions
17. Calculate the percentage yield for the Practical Calculating the formula of magnesium oxide (pages
125–6).
Answers will depend on Students’ results from the Practical.
18. Six tonnes of ethanol is produced from 15 tonnes of ethene when it is reacted with an excess of water.
Calculate the percentage yield of the reaction.
C2H4 (g) + H2O (g) → C2H5OH (g)
Relative molecular mass of ethene = (2 × 12) + (4 × 1) = 28
Relative molecular mass of ethanol = (2 × 12) + (6 × 1) + 16 = 46
So 28 tonnes of ethene produces 46 tonnes of ethanol
1 tonne of ethene produces (46/28) = 1.64 tonnes of ethanol
15 tonnes of ethene produces (15 × 1.64) = 24.6 tonnes of ethanol
6
Percentage yield 
 100  24.4 %
24.6
19. Find the percentage yield of the reaction if 5 g of CO2 is realised from the decomposition of 10 g of
CaCO3.
CaCO3 (s) → CaO (s) + CO2 (g)
41
WJEC GCSE Additional Science Teacher’s Notes
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100
Relative formula mass of calcium oxide = 40 + 16 = 56
So 100 g of calcium carbonate makes 56 g of calcium oxide.
1 g of calcium carbonate makes 0.56 g of calcium oxide
10 g of calcium carbonate makes 5.6 g of calcium oxide
5
Percentage yield 
 100  89.3 %
5.6
20. The combustion of ethanol: C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g).
Bonds broken:
5 × C–H = (5 × 412) = 2060 kJ
1 × C–C = (1 × 348) = 348 kJ
1 × C–O = (1 × 358) = 358 kJ
1 × O–H = (1 × 463) = 463 kJ
Total energy in = 3229 kJ
Bonds made:
4 × C=O = (4 × 743) = 2972 kJ
6 × O–H = (6 × 463) = 2778 kJ
Total energy out = 5750 kJ
Heat of combustion = 5750 – 3229 = 2521 kJ – EXOTHERMIC
21. The neutralisation of sodium hydroxide by hydrochloric acid:
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
ERRATUM Calculation Error: The neutralisation reaction of sodium hydroxide by
hydrochloric acid is exothermic.
22. The reaction of lithium with water: 2Li (s) + H2O (l) → 2LiOH (aq) + H2 (g)
ERRATUM Calculation Error: The reaction of lithium with water is exothermic.
23. The reaction of nitrogen and oxygen gas: N2 (g) + O2 (g) → 2NO (g)
Bonds broken:
1 × NN = 1 × 944 = 944
1 × O=O = 1 × 496 = 496
Total energy in = 1440 kJ
Bonds made:
2 × NO = 2 × 627 = 1254 kJ
Total energy out = 1254 kJ
Heat of reaction = 1254 – 1440 = –186 kJ – ENDOTHERMIC
42
WJEC GCSE Science Teacher’s Notes
12
Organic chemistry
_Alkanes and alkenes (pages 132–35)______________
PRACTICAL Making alkenes from alkanes
(pages 133–34)
This experiment is based on a practical from the Royal Society’s ‘Practical chemistry’ website
www.practicalchemistry.org/experiments/cracking-hydrocarbons,139,EX.html. Technical notes
are available from the link above.
Questions
1. Look at the structural formula in Figure 12.5. Is this chemical an alkane or an alkene? Give a reason for
your answer.
It is an alkene because it has a carbon-carbon double bond.
2. Alkenes are more reactive than alkanes. Suggest a reason for this, using your knowledge of their
chemical structure.
The double bond can be broken quite easily to attach to another atom. The structure of an
alkane is more stable.
_What’s the difference between a thermoplastic and a
thermoset? (pages 136–37)
TASK Why use this plastic? (page 137)
The answers to this task will depend on the plastic item chosen by the pupil.
44
WJEC GCSE Additional Science Teacher’s Notes
13
Water
_How do we get clean water? (pages 138–42)________
Questions
1. In areas of the world where the drinking water is not fully treated, or when the water is thought to have
been contaminated, people are asked to boil the water for several minutes and then cool it before
drinking it. Suggest the reason for this.
Boiling will kill many of the bacteria which may be in the water.
2. Suggest five ways in which an average home could reduce the amount of water used per day.
Possible suggestions:
 Have a shower rather than a bath.
 Don’t leave the tap running (e.g. when cleaning your teeth).
 Use economy flush on the toilet (where fitted) or put a brick in the cistern.
 Restrict the use of a hose to water the garden.
 Don’t wash the car too often.
 Collect rainwater to use for washing up or watering the garden.
 Maintain taps so that they don’t drip.
Five is quite a lot of ways to think of. This is deliberate, to promote some lateral thinking.
Discussion point
The water on the planet is constantly recycled by the water cycle, so why do we need to conserve water, if
what we use eventually finds its way back to rivers and reservoirs?
There would be no need to conserve water if more of it was accessible and if it was evenly
distributed, both in space and time. Points to consider:
 A lot of the water is salt water in seas and oceans. This is not easily available for direct use by
humans.
 Only about 1% of the world’s fresh water supply is accessible for direct use. Much of the rest
is deep underground or in inaccessible areas (e.g. polar ice).
 Some areas of the world have plentiful water, whereas other areas have insufficient. Transport
of water across the globe is difficult (and virtually impossible in the quantities needed in dry
areas).
 Rainfall is seasonal. Water may have to be conserved in the wetter periods for use in dryer
seasons. Water is particularly important during crop growing seasons, as this requires large
amounts of water.
Question
3. Find out why drinking salt water dehydrates you.
If cells come into contact with a solution which is more concentrated than their cytoplasm, they
will lose water by osmosis. Students will cover osmosis in the biology section.
45
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Separating ethanol and water (page 141)
Evaluate this method of separating ethanol and water. Are there any improvements that could be made
to the experimental method?
The main problem is using a Bunsen burner to heat the mixture to 78 °C. The temperature will
often exceed that and will be difficult to maintain. As only ethanol and water are present, this is
not a huge problem, but a thermostatic water bath would be better.
_How can we identify substances in a solution?_______
(pages 142–44)
PRACTICAL Who wrote the note? (page 144)
Preparation of ink samples:
You need at least two (preferably three) ink samples that are different in composition. It is
essential that only one of samples B, C and D matches A, but it would not matter if the other
two samples were the same. The inks can be found by simply trying different pens, or by
constructing the samples using mixtures of inks.
_What is gas chromatography? (pages 145–46)______
TASK How is solubility affected by temperature?
(pages 145–46)
This exercise will stretch more able pupils and will probably be too complex for lower ability
pupils.
1. How much sodium nitrate can dissolve in water at 30 °C?
95 g/100 cm3 water
2. Which compound is the least soluble at 50 °C?
Potassium chlorate
3. Which compound’s solubility is least affected by temperature?
Sodium chloride
4. How much extra potassium iodide can dissolve in 100 cm3 of water if the temperature is increased
from 15 °C to 30 °C?
25 g/100 cm3
5. Are the following solutions unsaturated, saturated or supersaturated?
a
40 g/100 cm3 sodium chloride at 75 °C
Saturated
46
WJEC GCSE Additional Science Teacher’s Notes
b
2 g/100 cm3 potassium chlorate at 45 °C
Unsaturated
c
155 g/100 cm3 potassium iodide at 15 °C
Saturated
d
100 g/100 cm3 sodium nitrate at 30 °C
Supersaturated
Note that pupils are not required to recall any information about supersaturated solutions.
The information is included here to test interpretation of the data.
6. Compare the solubility curves for potassium iodide and potassium nitrate.



Potassium iodide is more soluble than potassium nitrate over the whole range of
temperatures.
The solubility of both substances increases with temperature.
The solubility of potassium iodide increases at a constant rate (approx. 15 g/100 cm3 for
every 10 °C), whereas the solubility of potassium nitrate increases at a greater rate as the
temperature increases.
_What makes water hard or soft? (pages 147–49)____
PRACTICAL How can we tell the difference between
hard and soft water? (pages 147–48)
It is envisaged here that four different water samples are made up in the following ways:
 soft water – e.g. deionised water
 permanent hard water – e.g. using MgSO4
 temporary hard water – e.g. made by bubbling CO2 into lime water until the initial
precipitate just clears
 water sample with a mixture of permanent and temporary hardness.
1. Use your results to describe the hardness of each water sample, and whether this hardness is
temporary or permanent. Explain the reasons for your identification.
The answer will depend on the labelling of solutions and possibly the results. Temporary
hard water should be identified as removable by boiling.
2. This method works fairly successfully for comparing the hardness of the water samples. Suggest an
improvement that could be made if you wanted a more accurate measure of water hardness.
It would be necessary to use water samples of known hardness and to draw a calibration
curve to enable the results to be related to actual hardness.
TASK Is hard water good for your health? (page 149)
2. Why do you think the fact that hard water areas of the world tend to have lower rates of heart
disease than soft water areas is considered rather weak evidence for the hypothesis that drinking
hard water reduces heart disease?



The areas (both hard water and soft water) are likely to be very different from each other
so a truly ‘fair test’ is not possible.
The differences are small.
The results of different studies are variable/not very repeatable.
47
WJEC GCSE Additional Science Teacher’s Notes
Discussion point
On the basis of the evidence, do you think there is a case for adding calcium and magnesium salts to
drinking water in soft water areas?




There appears to be no evidence for a specific link between calcium salts in water and heart
benefits.
There is some evidence that magnesium salts (>10mg/l) have a protective effect.
No information is presented on any possible side-effects of these salts.
No evidence is presented on the effect of magnesium salts at the level suggested on the taste
of water.
48
WJEC GCSE Additional Science Teacher’s Notes
14
Simple electrical circuits
_ Simple electrical circuits (pages 153–61)__________
PRACTICAL Measuring currents in series and parallel
circuits (page 154)
Students set up series and parallel circuits to determine that current is the same all the way
around a series circuit, and that when current splits at a junction in a parallel circuit, the sum of
the currents going into the junction equals the sum of the current coming out of the junction.
This is best shown with bulbs of different powers.
Questions
1. Study the following circuits. Use your knowledge of the behaviour of current in series and parallel
circuits to calculate the current at each of the marked points on the circuit diagrams (a to j in Figure
14.6).
a 0.4 A
d 0.2 A
g 0.3 A
j 1.2 A
b 0.4 A
e 0.6 A
h 1.2 A
c 0.4 A
f 1.5 A
i 0.3 A
2. In a domestic house, all the electrical sockets, and all the domestic appliances such as an electric oven,
are connected in parallel to the main circuit board. In one such house during the early evening, the
lights are using 2.5 A, a television 0.5 A, an electric oven 13 A and a kettle 10 A. What is the total
current drawn from the main circuit board?
Total current = 2.5 + 0.5 + 13 + 10 = 26 A
3. Draw circuits showing the following:
a
Two bulbs and a switch in series with a
6 V power supply unit.
b
A solar cell connected in parallel with two filament
lamps, each one with its own switch in series.
49
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Measuring voltages in series and parallel
circuits (page 156)
Students set up series and parallel circuits to determine that the sum of the voltages into a series
circuit is the same as the sum of the voltages going out of the series circuit (within experimental
uncertainty) and that in parallel circuits, the voltage is the same across all components in
parallel.
Discussion points
1. How are the lights in your kitchen (or lounge) at home connected? Can you draw a circuit diagram
showing how they (and their switches) are connected to your mains fuse board? Do all the lights have
the same operating voltage and power (measured in watts)? Domestic electricity circuits are usually
connected in a ‘ring main’. Find out what this means and why domestic circuits are connected this way.
Domestic circuits are nearly always wired in parallel to the consumer unit. Each circuit with its
own circuit breaker, and the whole supply fitted with a main circuit breaker wired in series
with the consumer unit. There are a whole variety of mains light fittings – they usually have
the same mains voltage, but different powers. An example of a ring main is shown below.
Domestic circuits are connected this way for safety reasons – this circuit minimises accidents
through short circuits.
50
WJEC GCSE Additional Science Teacher’s Notes
2. Being an electrician or an electrical engineer is a really good job. You can work for yourself or for a
company. There are a great many opportunities at many different academic levels. Use the following
links to find out more about careers involving electricity:
www.careerswales.com www.connexions-direct.com
Investigate using the links above and also www.futuremorph.org
Questions
4. A 12 V solar panel is used to run three household bulbs as shown in Figure 14.10.
a
Bethany connected a voltmeter across the solar cell. What voltage would she measure during the
day?
12 V
b
Explain why her voltmeter would read 0 V at midnight.
No sunlight, so no generation of electricity.
c
During the day, Bethany connected the voltmeter across points A and B in the circuit and turned on
switch 1. What would her voltmeter read?
12 V
d
Explain why the lighting circuit has three switches. What does each switch do?
Switch 1 controls the whole circuit, switching it on and off, Switch 2 controls bulb 1 and
Switch 3 controls bulb 2 and bulb 3.
e
Give an example (from your house) of a circuit like this where two bulbs work off the same switch.
For example, wall lights in a lounge.
f
What is the advantage of connecting bulb 1 with one switch compared to bulbs 2 and 3 which have
one switch between them?
Bulb 1 can be controlled independently – bulbs 2 and 3 are controlled together – they are
either both ON or both OFF.
g
If bulb 2 and bulb 3 are exactly the same (same power rating and brightness), what voltage would
Bethany measure if she closed all the switches and connected her voltmeter across points A and C
in the circuit?
6V
h
Why would the voltage rating of bulb 1 be different from the voltage ratings of bulbs 2 and 3?
Bulb 1 has 12 V connected across it, whereas bulbs 2 and 3 only have 6 V across them.
5. Measuring voltages in simple circuits in school is quite safe.
a
Why do electricians have to be much more careful when they are measuring voltages across
components in a household wiring circuit?
The voltages and the currents are usually much higher so the risk of electrocution is higher.
b
What precautions do you think that they can take to minimise the risks to themselves?
Good training, turning off the mains when working on any circuit, ensuring all earth
connections are connected, making sure the circuit breakers/fuses are working.
51
WJEC GCSE Additional Science Teacher’s Notes
c
Why is it always a good idea to ask an electrician to do electrical work on your house, if you don’t
really know what you are doing?
Electricians are trained to do mains electrical work safely.
6. Copy and complete Table 14.1 converting ohms to kilohms to megohms.
Remember:
1 MΩ = 1 000 000 Ω = 1000 kΩ
1 kΩ = 0.001 MΩ = 1000 Ω
1 Ω = 0.001 kΩ = 0.000 001 MΩ
Resistance in ohms, Ω
Resistance in kilohms, kΩ
Resistance in megohms, MΩ
1 000 000
1 000
4 000
4
0.004
0.002
0.000 002
3 000
3
0.003
220 000
220
0.220
6 000 000
6 000
10 000
10
2
1
6
0.010
PRACTICAL Measuring current and voltage in circuits
controlled by a variable resistor (page 159)
1. Graphs of voltage against current for components are called ‘electrical characteristics’. Plot electrical
characteristic graphs for the fixed resistor and the bulb. If you can, plot them both on the same graph
using the same axes.
Student graphs should resemble the one below. The red line is for the fixed resistor, the blue
line for the bulb.
52
WJEC GCSE Additional Science Teacher’s Notes
2. Describe in words the pattern of each graph. This means that you have to describe how the voltage
(on the y-axis) varies with the current (on the x-axis).
Resistor – voltage is proportional to current (graph is linear with a positive gradient).
Bulb – voltage increases faster than current (graph is curved with increasing positive
gradient).
3. Explain how a variable resistor can be used in a circuit to control the current through and the voltage
across other components.
Altering the resistance of a circuit alters the current flowing through the circuit. If the
current is altered then the voltage across the other components will change due to Ohm’s
law.
Questions
7. Using the data that you collected for the Practical: Measuring current and voltage in circuits
controlled by a variable resistor, construct two tables. One table will be for the fixed resistor data,
and the other table will be for the bulb.
The values in the table will depend on the students’ results from the Practical.
8. Describe the patterns in your results for Question 7. How does the resistance of the fixed resistor vary
with current (or voltage)? How does the resistance of the bulb vary with current (or voltage)?
The resistance of the fixed resistor is constant for different values of current (or voltage).
The resistance of the bulb will increase with an increasing current (or voltage).
9. A 25 Ω fixed resistor has a current of 2 A through it. Calculate the voltage across the fixed resistor.
V = I × R; V = 2 × 25 = 50 V
10. In a mobile phone circuit, 1.5 V is applied across a keyboard circuit with a resistance of 5000 Ω. What is
the current in the keyboard circuit?
V  I  R so I 
V
1.5

 0.003 A
R 5000
11. Figure 14.13 shows the electrical characteristic of a 12 V car bulb. Use the graph to calculate the
resistance of the bulb when the current through the bulb is:
a
0.2 A
V = 0.4 V so R =
0.4
=2
0.2
b
0.6 A
V = 3.6 V so R =
3.6
=6
0.6
c
1.0 A
V = 10.0 V so R =
10.0
= 10 
1.0
12. Explain why the resistance of a bulb changes when more current is passed through it. (Hint: when the
bulb has more current going through it, it is brighter and hotter. How might this affect the structure of
the metal filament?)
As more current flows through the filament, there will be more collisions of the free electrons
with the structure of the metal filament and the electrons themselves. This heats the filament
53
WJEC GCSE Additional Science Teacher’s Notes
causing the positive ion cores of the filament to vibrate more, causing even more collisions
with the free electrons, increasing the resistance of the filament.
13. A rheostat (large variable resistor) is set up with a resistance of 12 Ω. A 0–12 V variable power supply
is connected in series with an ammeter and the rheostat.
a
Draw a circuit diagram of this arrangement.
b
Use the data supplied and Ohm’s law to determine the current through the rheostat, for voltages of
0 V, 2 V, 4 V, 6 V, 8 V, 10 V and 12 V.
I
V
R
Voltage, V, (V)
0
2
4
6
8
10
12
Current, I, (A)
0.00
0.17
0.33
0.50
0.67
0.83
1.00
c
Plot an electrical characteristic graph of the rheostat. Plot the voltage on the y-axis and the current
on the x-axis. Draw a best-fit line through the points and label this line ‘12 Ω’.
d
Calculate the gradient (slope) of the best-fit line. Compare this value to the resistance of the
rheostat.
Gradient = 12 – the same as the resistance of the rheostat.
e
The resistance of the rheostat is now changed to 6 Ω. On the same electrical characteristic graph,
sketch the graph for the new resistance setting and label this ‘6 Ω’. Explain why you have drawn
the sketch line where it is.
The resistance is halved so the gradient will halve – the line will go through (1.0, 6).
54
WJEC GCSE Additional Science Teacher’s Notes
_ Electrical power (pages 162–63)_________________
Questions
14. Calculate the power of a 6 V torch bulb drawing a current of 0.8 A.
P = V × I = 6 × 0.8 = 4.8 W
15. A current of 5 A passes through a lamp with a resistance of 2.4 Ω, and then through a small cooling fan
of resistance 4 Ω. Calculate the power of each component and hence calculate the total power drawn
from the circuit.
Lamp: P = I2 × R = 52 × 2.4 = 60 W
Fan: P = I2 × R = 52 × 4 = 100 W
Total power = 160 W
16. Study the circuit diagram in Figure 14.14.
a
Calculate the power of each bulb.
6  bulb: P = I2 × R = 2.52 × 6 = 37.5 W
12  bulb: P = I2 × R = 2.52 × 12 = 75 W
b
Calculate the total power drawn from the power supply.
Total power = 37.5 + 75 = 112.5 W
c
Calculate the voltage of the power supply.
V
d
P 112.5

 45 V
I
2.5
Calculate the voltage across each bulb.
6  bulb: V = I × R = 2.5 × 6 = 15 V
12  bulb: V = I × R = 2.5 × 12 = 30 V
17. A mains hairdryer operates with a voltage of 220 V.
a
Calculate the power when it is on its HIGH setting, drawing a current of 8 A.
P = V × I = 220 × 8 = 1760 W
b
The LOW setting operates with a power of 1 kW (1000 W). Calculate the current flowing through the
hairdryer.
I
c
P 1000

 4.5 A
V 220
The hairdryer can also be used in the United States where the mains voltage is different. The power
given out by the hairdryer is the same as in the UK (your answer to part a), but the current flowing
through the hairdryer is 16 A. Calculate the voltage of the mains in the USA.
V
P 1760

 110 V
I
16
55
WJEC GCSE Additional Science Teacher’s Notes
15
Distance, speed and
acceleration
_ Measuring speeds (pages 165–67)_______________
TASK The animal olympics 100 m final (pages 166–67)
1. Each animal finishes the 100 m race. Use the data to calculate the times for each competitor.
Animal
Cheetah
Pronghorn antelope
Lion
Springbok
Horse
Elk
Coyote
Usain Bolt
Top speed
(m/s)
31
27
22
22
21
20
19
19
Distance
travelled (m)
100
100
100
100
100
100
100
100
Time (s)
3.2
3.7
4.5
4.5
4.8
5.0
5.3
5.3
2. Explain why, in reality, the times for each competitor will be higher than those that you have
calculated.
The animals (and Usain Bolt) do not run at top speed for the whole race, they start at 0 m/s
and accelerate to top speed.
3. Usain Bolt broke the World 100 m record in the Beijing Olympic final in 2008, and this record
breaking run has been one of the most closely analysed runs in history, although he subsequently
broke his own world record in the 2009 World Championships. Usain Bolt’s mean times for the 2008
final race were as shown in Table 15.2.
a
Make a copy of this table, but add a third column labelled ‘Average speed, m/s’. Calculate Usain
Bolt’s mean speed for each 10 m segment of the race and fill in your table.
Distance (m)
Reaction time to leave blocks
0–10 (including reaction time)
10–20
20–30
30–40
40–50
50–60
60–70
70–80
80–90
90–100
0–100
Split time (s)
0.165
1.85
1.02
0.91
0.87
0.85
0.82
0.82
0.82
0.83
0.90
9.69
Average speed in
segment (m/s)
0.0
5.4
9.8
11.0
11.5
11.8
12.2
12.2
12.2
12.0
11.1
10.3
56
WJEC GCSE Additional Science Teacher’s Notes
b
Plot a graph of Usain Bolt’s mean speed (on the y-axis) against distance (on the x-axis). Take
the mean speed to occur in the middle of each 10 m segment of the race, so plot the distances
as: 5 m, 15 m, 25 m and so on up to 95 m.
See graph under part (d) below.
c
Describe the pattern (or shape) of the graph and try to explain how mean speed varies with
distance.
The average speed increases from zero to about 10 m/s in a distance of 15 m – as Usain
was accelerating out and away from the blocks. After 15 m, the average speed increases
more slowly up to a maximum of just over 12 m/s for about 70 m – when Usain was
running at maximum speed. After this Usain slowed back to about 11 m/s for the last 15
m – as he was lunging for the line.
d
In 2009, the Cincinnati Zoo’s 8-year-old female cheetah Sarah became the world’s fastest land
mammal. Sarah covered 100 m in a time of 6.13 seconds, breaking the previous mark of 6.19
seconds set by a male South African cheetah named Nyana in 2001. Use this information
(assuming that a cheetah will have a similar pattern of running to Usain Bolt) to sketch on the
same graph the pattern for Sarah compared with Usain Bolt.
Sarah the cheetah
Usain Bolt
Discussion points
1. You can find lots of videos of Usain Bolt’s 2008 Olympic 100 m final online. Watch the race. It
almost feels as if he is slowing down at the end and waving to the crowd, yet in reality he’s still
running at top speed. How much faster do you think human beings can run? Is there going to be an
ultimate ‘top speed’ or do you think that humans will get progressively quicker and quicker?
Many suitable links are available on youtube.com. Some interesting views on how fast a
human being can run are available from Peter Weyand from Southern Methodist University,
USA:
http://smu.edu/education/APW/LocomotorNews.asp
2. The cheetah has a substantially faster top speed than most of its prey (for example the springbok),
yet it only has a 50% kill success rate. Why do you think that half of the cheetah’s prey get away?
Cheetahs can reach a speed approaching 70 mph (110 km/h), however this speed can be
maintained for only a few hundred metres or for about one minute. If it is forced to run
longer than a minute, it usually gives up the chase.
57
WJEC GCSE Additional Science Teacher’s Notes
_ Speed or velocity? (page 168)___________________
Discussion points
Many D of E expeditions involve multiple routes in many directions. Why is it important that D of E
assessors and group leaders know the average walking speed of a group over given terrains, and must
ensure that all group members can read a compass correctly?
By knowing the average walking speed of a group, the assessor knows the average distance that
the group can travel in a given time. If the group can read a compass, then the assessor can judge
when to meet them at pre-determined checkpoints.
_Acceleration: speeding up and slowing down________
(pages 168–70)
Questions
1. Table 15.3 shows some data for some of the world’s fastest production cars, and for comparison, a
standard Ford Focus 1.8. Copy and complete the table (without the pictures) by calculating the
acceleration of each car.
Car
Bugatti Veyron Super Sport
Ariel Atom V8
Porsche 911 Turbo S
Nissan GT-R
Maclaren MP4-12C
Ford Focus 1.8
Time (s) to reach 100 km/h
(27.7 m/s) from a standing start
2.4
2.5
2.7
2.8
3.1
10.3
Acceleration (m/s2)
11.5
11.1
10.3
9.9
8.9
2.7
2. Travelling on a motorway, HGV lorries are usually speed limited to 60 mph or 27 m/s. A Ford Focus 1.8
travelling behind an HGV lorry travelling at 27 m/s accelerates to 70 mph or 31 m/s in 2 seconds, in
order to overtake the HGV lorry. What is the acceleration of the Ford Focus? How does this compare
with its maximum acceleration?
acceleration 
change in velocity 31 - 27 4

  2 m/s
2
time
2
_Graphs of motion (pages 170–72)________________
Questions
3. Describe the motion of the objects illustrated by the distance–time graphs (a), (b) and (c) in Figure 15.6.
a
Object moving at a constant speed for 5 s.
b
Object stationary 20 m away from an origin for 5 s.
c
Object moving at a constant speed for 20 s, then at a slower constant speed for 20s.
4. Calculate the mean velocity of the object moving in (a).
6 m/s
5. Calculate the two mean velocities illustrated by distance−time graph (c).
10 m/s then 5 m/s
58
WJEC GCSE Additional Science Teacher’s Notes
6. Sketch distance−time graphs for the following:
a
An object moving 20 m in 4 s, then stationary for 3 s, then moving back to the start in 8 s.
25
distance (m)
20
15
10
5
0
0
2
4
6
8
10
12
14
16
tim e (s)
b
An object stationary for 2 s then moving at a constant velocity of 5 m/s for 10 s, then stationary for
another 2 s.
60
distance (m)
50
40
30
20
10
0
0
2
4
6
8
10
12
14
16
tim e (s)
An object moving 10 m in 5 s, then moving in the same direction at a constant velocity of 4 m/s for
3 s, then moving back to the start in 4 s.
25
20
distance (m)
c
15
10
5
0
0
2
4
6
8
10
12
14
tim e (s)
59
WJEC GCSE Additional Science Teacher’s Notes
PRACTICAL Measuring, plotting and analysing real
distance–time graphs (pages 171–72)
A student will need to be primed to bring in a bicycle (with helmet) before-hand. This practical
task requires quite a lot of organisation – a schematic diagram of who is doing what and
standing where will help considerably – go through this in the laboratory before going outside.
A suitable data recording sheet could look like:
Motion
Time to reach 5 m cone (s)
Time to reach 10 m cone (s)
Time to reach 15 m cone (s)
Time to reach 20 m cone (s)
Time to reach 25 m cone (s)
Time to reach 30 m cone (s)
1 2 3 Av 1 2 3 Av 1 2 3 Av 1 2 3 Av 1 2 3 Av 1 2 3 Av
Walking
Running
Cycling
Answers to the ‘Analysing your results’ questions will depend on the results gathered.
_ Velocity–time graphs (pages 172–74)____________
Question
7. Describe the motion of the objects illustrated by the velocity–time graphs in Figure 15.8. For each graph
calculate any accelerations/decelerations and (HT only) the total distance travelled.
a
(Top left)
Object stationary for 2 s then accelerating at 3 m/s2 for 2 s, reaching
maximum velocity of 6 m/s, then travelling at constant 6 m/s in same direction
for 6 s
b
(Middle left)
Object accelerating at 3 m/s2 for 3 s, reaching velocity of 9 m/s, then
travelling at a constant 9 m/s in the same direction for 4 s before decelerating
(in the same direction) at 3 m/s2 (or accelerating at –3m/s2) for 3 s before
coming to rest at t = 10 s
c
(Bottom left) Object accelerating at 4 m/s for 2 s, reaching velocity of 8 m/s, then
2
decelerating (in the same direction) at 2 m/s2 (or accelerating at –2m/s2) for
4 s before accelerating again at 3m/s2 in the same direction for 3 s reaching a
velocity of 9 m/s before decelerating (in the same direction) at 9 m/s2 before
coming to rest at t = 10 s
d
(Top right)
Object initially travelling at 9 m/s, decelerating at 3 m/s2 for 3 s, coming to
rest at t = 3 s, then accelerating (in the same direction) at 2 m/s2 for 4 s
reaching a velocity of 8 m/s and then travelling at this constant velocity for 3 s
e
(Top right)
Object travelling at a constant velocity of 6 m/s for 3 s then accelerating at 2
m/s2 for 1 s, reaching velocity of 8 m/s and staying at this constant velocity of
8 m/s for 1 s before decelerating (in the same direction) at 2 m/s2 (or
accelerating at –2m/s2) for 4 s before coming to rest at t = 9 s
60
WJEC GCSE Additional Science Teacher’s Notes
16
The effect of forces
_ Moving in space (pages 176–78)_________________
Discussion point
What would it be like to live for 180 days on the ISS (a typical mission duration)? What sort of things in your
daily routine would be difficult on the ISS in low Earth orbit?
Many websites chronicle the daily life of astronauts and cosmonauts on-board the ISS. Examples
include:
www.scienceinschool.org/2008/issue10/iss
www.nasa.gov/audience/foreducators/teachingfromspace/dayinthelife/index.html
PRACTICAL Analysing the gravitational field strength of
the Earth (page 177)
This is a straight-forward activity that could be extended by giving students a range of different
balances and newton meters.

1. For each slotted mass combination, calculate the sum  g 

weight in N 
, and record this in the
mass in kg 
last column of the table.
Values should be approximately 10 N/kg
2. Look at the values of g that you have calculated – is there a pattern?
The values should all be approximately the same (~10 N/kg).
3. Calculate the average value of g.
Value depends upon values recorded by students (~10 N/kg).
4. Use the range of the values to state an uncertainty on your value of g, i.e. g = (average value ±
uncertainty) N/kg.
A reasonable way to calculate the uncertainty is ±(range/2).
5. Plot a graph of weight (N) on the y-axis against mass (kg) on the x-axis.
Student graph
6. Draw a best-fit straight line through your points (make sure your line goes through the origin).
Best-fit line
7. Calculate the gradient (slope) of your best-fit line. Compare your value with the average value of g
that you calculated earlier. The gradient of this line is the value of g.
gradient 
vertical displacement
≈ 10 N/kg
horizontal displacement
Values should be very similar.
61
WJEC GCSE Additional Science Teacher’s Notes
8. The value of g is approximately 10 N/kg. How close to this value is:
a your average calculated value?
b the gradient of your graph?
Calculated deviations from 10 N/kg should be very small.
9. How could you use your graph to determine a value of the uncertainty of the value of g?
Plot range bars and get a range of different ‘best-fit’ lines (maximum/minimum/best-fit).
10. Why is it more accurate to measure the weight of a slotted mass with a Newton meter with the
lowest range capable of measuring it?
Lower ranges will have greater precision.
11. Would it be better to measure all the weights with the same (bigger ranged) Newton meter?
This leads to an interesting discussion of precision v zero-ing errors. Answer: depends on
the quality of the Newton meter.
Discussion point
When we are living in the Earth’s gravitational field we live in a world of 1 g, that is, 1 × the Earth’s
gravitational field. At take-off, the astronauts experience 3 g (3 × the Earth’s gravitational field strength). In
orbit, the astronauts effectively experience 0 g. What do you think these gravitational fields ‘feel’ like?
There is an interesting interview with Dr Mae Jemison (STS-47 Shuttle Endeavour 1992):
http://teacher.scholastic.com/space/mae_jemison/interview.htm
Questions
1. A typical ISS module has a mass of 22 700 kg. Each of the two Space Shuttle solid rocket boosters has
a lift-off mass of 590 000 kg, and the external fuel tank (filled with rocket fuel) has a lift-off mass of 760
000 kg.
a
Calculate the weight of each component of the Space Shuttle launch system.
Space Shuttle: mass = 78 000 kg  weight = 780 000 N
ISS Module: mass = 22 700 kg  weight = 227 000 N
Solid rocket booster: mass = 590 000 kg  weight = 5 900 000 N (×2 = 11 800 000 N)
External fuel tank: mass = 760 000 kg  weight = 7 600 000 N
b
What is the total lift-off weight of the Space Shuttle launch system?
Total weight at take off = 20 407 000 N
c
What is the minimum total thrust needed by the Space Shuttle main engines and the solid fuel
rocket boosters? Why is this a ‘minimum’?
Minimum thrust = total weight = 20 407 000 N
The total thrust of the engines does not act directly downwards – some of the thrust acts at
an angle to the vertical as the combustion products come out of the jet engines.
2. The last Space Shuttle launch took place in June 2011. From that point on, the ISS will be serviced via
Russian Progress and American Dragon spacecraft whilst astronauts will travel to and from the ISS in
Russian Soyuz spacecraft. All Russian spacecraft are launched via Soyuz-2 rockets and the American
spacecraft will be launched with Falcon 9 rockets (Table 16.2). Copy and complete the table,
calculating the launch weight of each rocket and the minimum resultant upwards force at launch.
62
WJEC GCSE Additional Science Teacher’s Notes
Rocket
Launch
mass (kg)
Falcon 9
Soyuz-2
340 000
310 000
Launch
weight (N)
3 400 000
3 100 000
Launch
thrust (N)
4 500 000
4 000 000
Minimum
resultant upwards
force at launch (N)
1 100 000
900 000
_Inertia and Newton’s first law of motion___________
(pages 178–80)
PRACTICAL How well does Newton’s first law work on
Earth? (page 180)
1. Plot a graph of velocity of the glider (y-axis) against distance from the start of the LAT (x-axis).
Graph should be linear (horizontal) – apart from the first portion up to the first light gate.
2. Draw a best-fit line through your points. If your glider obeys Newton’s first law then the velocity of
the glider will not change as it travels down the LAT and all the velocities will be exactly the same.
Graph should be linear (horizontal) – apart from the first portion up to the first light gate.
3. Does your glider obey Newton’s first law?
This depends on the best-fit line drawn, but probably yes.
4. Why might the velocity of the glider change as it moves down the track?
Air-resistance could slow the glider down. The air-track needs to be horizontal, otherwise
the glider will accelerate/decelerate.
5. Use your data to decide how repeatable this experiment is.
Students should plot range-bars on graph to judge the spread of the data.
Further experiments:
1. You can introduce more friction into the experiment by turning down the air blower – what happens
then?
Introducing more friction causes the glider to decelerate and slow down.
2. What happens when you increase the inertia of the glider by stacking masses on it?
Velocity is lower (mass is bigger). Eventually, the extra weight on the glider causes it to
come into contact with the LAT, causing friction and slowing the glider down.
_ Momentum (pages 180–81)_____________________
Questions
3. Calculate the momentum of a 5 kg toolbag travelling at 7700 m/s.
p = mv = 5 × 7700 = 38 500 kg m/s
4. Calculate the momentum of the ISS (mass = 400 000 kg), also travelling at 7700 m/s.
63
WJEC GCSE Additional Science Teacher’s Notes
p = mv = 400 000 × 7700 = 3 080 000 000 kg m/s
5. At take-off, the Space Shuttle leaves the launch tower travelling at 45 m/s. The momentum of the
Shuttle at this point is 90 000 000 kg m/s. What is the mass of the Shuttle at this point? Why isn’t the
mass of the Shuttle constant?
p 90 000 000

 2 000 000 kg
v
45
As fuel is used up, the mass goes down.
p = mv  m 
6. When the solid rocket boosters and the external fuel tank are jettisoned, the Space Shuttle has a
momentum of 140 000 000 kg m/s, and a mass of 100 700 kg. What is the velocity of the Shuttle at this
point?
p = mv  v 
p 140 000 000

 1390 m/s
100 700
m
7. Use the mass and momentum information in these questions and the rest of the text to describe how
the mass, velocity and momentum of the Shuttle change during its flight up to docking with the ISS.
What is the final momentum of the Shuttle just before docking with the ISS?




On launch pad before engine on: mass constant, velocity zero, momentum zero
At moment of take-off: mass decreasing, velocity increasing, momentum increasing
Up to jettison of tanks: mass decreasing, velocity increasing, momentum increasing
Orbit just before docking (engines off): mass constant, velocity constant, momentum
constant
_The forces and motion at take-off (pages 181–84)____
Discussion point
A Space Shuttle (mass = 78 000 kg) docks with the ISS (mass = 385 471 kg). At the moment of docking the
ISS is effectively stationary and the Space Shuttle is moving at 2 m/s relative to the ISS. What are the
relative momentums of the Space Shuttle and the ISS before docking, and what is their combined
momentum after docking? What is the effective increase in speed of the ISS? What does this tell you about
momentum and collisions?
Relative momentum of Space Shuttle = mv = 78 000 × 2 = 156 000 kg m/s
Relative momentum of ISS = 0 kg m/s
Combined relative momentum after docking = 156 000 kg m/s
p
156 000
p = mv  v  
 0.34 m/s
m (78 000  385 471)
Momentum is conserved during collisions.
PRACTICAL Investigating Newton’s second law
(pages 182–83)
This experimental demonstration works best using data-logging software that calculates
acceleration directly. Remember to pre-load the glider with weights that can be transferred to
the mass stack so that the total accelerating mass remains constant.
1. Calculate values of force/acceleration in your table and record them.
Calculated values will depend upon data obtained.
64
WJEC GCSE Additional Science Teacher’s Notes
2. Is there a pattern in your results? What is the average value of force/acceleration? How does this
compare to the mass (in kg) of the glider plus slotted masses?
F/a should be constant with a value (approximately) equal to the total accelerating mass
(glider + mass stack).
3. Plot a graph of resultant force (y-axis) against acceleration (x-axis). Confirm that it is a straight line
and draw a best-fit straight line through your results (starting at the origin).
Student graphs.
4. Measure and calculate the gradient (slope) of the graph.
5. Compare your gradient to the mass (in kg) of the glider plus the slotted masses.
Gradient should (approximately) equal total accelerating mass.
Questions
8. A fully laden Soyuz spacecraft (mass = 7150 kg) accelerates away from the ISS towards its re-entry
point with an acceleration of 2 m/s2 relative to the ISS. Calculate the resultant force on the Soyuz
spacecraft.
F = ma = 7150 × 2 = 14 300 N
9. At lift-off, the combined thrust of the SRB and main Shuttle engines is 30 400 000 N. The total weight of
the Space Shuttle at lift-off is 20 407 000 N, as its mass is 2 040 700 kg.
a
Calculate the resultant force on the Space Shuttle at take-off.
Resultant force = thrust – weight = 30 400 000 – 20 407 000 = 9 993 000 N
b
Calculate the acceleration of the Space Shuttle at take-off.
F = ma  a 
F 9 993 000

 4.9 m/s 2
m 2 040 700
10. An astronaut is using the manned manoeuvring unit (MMU) to examine solar panels on the ISS. The
MMU generates a small thrust force of 60 N, which accelerates the MMU and the astronaut at 0.25
m/s2. Calculate the mass of the MMU plus the astronaut. If the astronaut has a mass of 80 kg, what is
the mass of the MMU?
F = ma  m 
F
60

 240 kg  mass of MMU = 240 – 80 = 160 kg
a 0.25
_ Newton’s second law and momentum_____________
(pages 184–87)
Questions
11. During T+200 s and T+300 s of a Space Shuttle launch (i.e. between 200 s and 300 s after launch), the
Shuttle (mass = 2 040 700 kg) accelerates from 2600 m/s to 4400 m/s.
a
b
Calculate the momentum of the Shuttle at:
i
T+200 s
p = mv = 2 040 700 × 2 600 = 5 306 000 000 kg m/s
ii
T+300 s
p = mv = 2 040 700 × 4 400 = 8 979 000 000 kg m/s
Calculate the change in momentum between these times.
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WJEC GCSE Additional Science Teacher’s Notes
Δp = 8 979 000 000 – 5 306 000 000 = 3 673 000 000 kg m/s
c
Calculate the resultant force acting on the Shuttle during this time.
F
d
p 3 673 000 000

 36 731 000 N
t
100
During this time, the Shuttle is both gaining altitude and losing mass. Explain how both of these will
affect the forces acting on the Shuttle.
Weight decreases (Shuttle further from Earth so g decreases, and mass is decreasing). So
resultant force increases (thrust remains constant until jettison of tanks and boosters).
12. In preparation for docking with the ISS, a manned Soyuz spacecraft (mass = 7150 kg) changes velocity
relative to the ISS from 12.0 m/s to 0.5 m/s.
a
Calculate the change in momentum of the Soyuz.
Δp = mΔv = 7150 × (12.0 – 0.5) = 82 225 kg m/s
b
Calculate the resultant decelerating force acting on the Soyuz.
(No time data given) … assuming change of momentum takes 10 s:
p 82 225
F

 8222.5 N
t
10
c
The Soyuz has three ‘retro-rockets’ that are used to decelerate the Soyuz before docking. Explain
how these rockets can decelerate the Soyuz.
Retro rockets provide thrust force in opposite direction to direction of motion of Soyuz –
Newton’s Second Law then gives deceleration.
_Touch down! (pages 186–187)___________________
PRACTICAL Making a model of a Soyuz descent module
(page 187)
Safety: ensure students are safe and stable if they are dropping objects from a height.
Provide students with a range of different suitable materials and resources (glue/scissors/
sellotape/tape measures/stopwatches, etc).
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WJEC GCSE Additional Science Teacher’s Notes
17
The physics of rugby
_ Energy and work (pages 189–92)________________
Questions
1. What is meant by ‘work done’?
Work is done when energy changes form.
2. What are the units of work done?
Joules
3. What factors dictate the amount of work done by a player in a lineout lifting a jumper?
Number of players lifting the jumper, weight of the jumper, distance lifted.
4. In a driving maul, players pushing to drive the maul forward typically push with an average force of
750 N. If the driving maul is pushed 8 m, how much work does a typical player do?
work done = force × distance = 750 × 8 = 6000 J
5. During a scrum (Figure 17.3), eight players each push with an average force of 600 N, moving the
scrum 2.5 m.
a
What is the total force exerted by all eight players?
total force = 8 × 600 = 4800 N
b
Calculate the total work done moving the scrum.
work done = force × distance = 4800 × 2.5 = 12 000 J
6. In a head-on driving tackle, a rugby player does 1650 J of work driving the opponent backwards by 3 m.
Calculate the force of the tackler.
work done = force × distance
work done 1650
force 

 550 N
distance
3
7. Calculate the distance that a line-out jumper is lifted if the player lifting the jumper exerts a force of
950 N and does 1520 J of work.
work done = force × distance
work done 1520
distance 

 1.6 m
950
force
8. What is meant by the efficiency of an energy transfer?
Efficiency is a measure of how much useful energy comes out from an energy transfer
compared to how much total energy goes in.
67
WJEC GCSE Additional Science Teacher’s Notes
9. Why is heat normally ‘wasted’ during an energy transfer?
During energy transfers where heat is produced, the heat is normally lost into the surroundings,
and cannot be recovered.
10. Why are muscles only 25% efficient?
75% of the energy produced in muscles is wasted as heat as the muscles contact and relax
11. How do our bodies deal with the heat produced by our muscles when we exercise?
The excess heat is controlled via homeostasis by sweating, vasodilation of capillaries near the
surface of the skin and the flattening of skin hairs.
PRACTICAL How much work do you do? (page 192)
Students need to measure the distances moved by the different weights (vertically) and calculate
the weights using weight = mg, or by direct measurement via a newton meter.
Students should take care measuring the distances to ensure that the rulers/tape measure/fingers
do not get caught in the machines.
If students are measuring forces directly with a newton meter, loops of string would be useful to
put round the machine handles so that the newton meters can be attached.
If students calculate the efficiency of each machine, a bar chart would be a suitable way of
illustrating the results.
_ Running with a rugby ball – analysing kinetic energy
(pages 193–94)
Questions
12. What is meant by kinetic energy?
The energy possessed by a moving object.
13. What does the kinetic energy of a rugby player depend upon?
Mass of object and velocity of object.
14. If a rugby player jogs at 5 m/s and then sprints at 10 m/s, she doubles her velocity. By what factor does
her kinetic energy increase?
KE is proportional to v 2, so if v doubles, KE goes up by a factor of 22 = 4.
15. At a recent Wales squad training session, the sprinting performance of various players was measured
and recorded. Table 17.1 summarises the findings of the fitness director. Copy and complete the table
(minus the photos), calculating the maximum kinetic energy of each player.
AlunWyn Jones: 4994 J
Shane Williams: 5018 J
Adam Jones: 4588 J
James Hook: 5029 J
16. A standard (size 5) rugby ball has a mass of 0.44 kg. When kicking from a tee, James Hook can kick
the ball with an initial velocity of 24.5 m/s. Calculate the initial kinetic energy of the ball.
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WJEC GCSE Additional Science Teacher’s Notes
KE = ½ mv 2 = 0.5 × 0.44 × 24.52 = 132 J
PRACTICAL Measuring the kinetic energy of a rugby ball
(page 194)
This is a simple straight-forward task. Students calculate the average velocity of the ball by
measuring the time it takes to travel a set distance (this gets more accurate as the distance
increases). The main aim of the exercise is to get students thinking about a range.
The main hazard in this experiment is being hit accidentally by a fast-moving ball – students
can work out suitable control measures to minimise harm from this risk.
_ Kicking a ball – an exercise in gravitational potential _
energy (pages 194–97)
Questions
17. What is meant by ‘gravitational potential energy’?
The energy stored in an object due to it being moved through a vertical distance in a
gravitational field.
18. Apart from the gravitational field strength, what two other factors dictate the gravitational potential
energy of a rugby ball?
Mass of the object and vertical distance moved.
19. Rugby balls come in three main sizes: (size 3 (ages 6–9) mass = 0.28 kg, size 4 (ages 10−14) mass =
0.38 kg, size 5 (adult) mass = 0.44 kg). During a media press photo-shoot for a ball sponsor, James
Hook kicks all three balls to the same height (35 m). If the gravitational field strength is 10 N/kg,
calculate the gravitational potential energy gained by each ball at the top of the kick.
Size 3: PE = mgh = 0.28 × 10 × 35 = 98 J
Size 4: PE = mgh = 0.38 × 10 × 35 = 133 J
Size 5: PE = mgh = 0.44 × 10 × 35 = 154 J
20. Wales hooker Matthew Rees throws the ball into a lineout from an initial height of 2.0 m. The ball gets
to a maximum height of 4.2 m, gaining a gravitational potential energy of 9.9 J. If the gravitational field
strength is 10 N/kg, calculate the mass of the ball.
Vertical distance travelled by ball = 4.2 – 2.0 = 2.2 m
9.9
PE
PE  mgh m 

 0.45 kg
gh 10  2.2
PRACTICAL Gravitational potential energy and the rugby
lineout (page 196–97)
Safety: Ensure that the two students lifting the third student are capable of lifting the jumper,
and that the jumper is reasonably agile. This activity must be performed on gym or crash mats.
Consult with PE staff before doing this activity. This could be done as a demonstration using
suitably trained students (rugby players). Suitable, non-contact alternatives are suggested using
different balls.
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WJEC GCSE Additional Science Teacher’s Notes
_ Scrummaging – a case study in Newton’s third law __
(pages 197–99)
Questions
21. What is Newton’s third law?
For every action force, there is an equal and opposite reaction force.
22. What are the names of the two forces in an interaction pair?
Action force and reaction force.
23. What are the two main types of force?
Contact forces and action at a distance forces.
24. Explain why a rugby player involved with pushing in a maul would only fall on to the ground if she
slipped or if the maul collapsed.
All the forces acting on her would be in balanced pairs. This means no net resultant force on
her, so she will stay on her feet.
25. Look at the following diagrams. Sketch each diagram and label the force interaction pairs in each case.
action of sprinter
on block
reaction of
skateboard on
skateboarder
reaction of block
on sprinter
reaction of water
on bottle
action of
skateboarder on
skateboard
action of air
pressure on
water
70
WJEC GCSE Additional Science Teacher’s Notes
18
Cars, the Highway Code
and collisions
_ Total stopping distance of a vehicle (pages 200–3)___
Questions
1. For a vehicle, what is the:
a
thinking distance
The distance that the vehicle travels whilst the driver sees the hazard, thinks about braking
and then actually reacts to put the brakes on.
b
braking distance
The distance that the vehicle moves while the brakes are being applied.
c
total stopping distance?
total stopping distance = thinking distance + braking distance
2. State and explain two factors that affect the thinking distance of a stopping car.
Velocity of car, reaction time of the driver, driver distractions, use of mobile phone/radio/mp3/
Sat Nav, being drunk or under the influence of drugs, etc. Each factor needs a reasonable
explanation.
3. Do you think that smoking whilst driving a car affects the total stopping distance? Explain your answer.
Smoking does affect the total stopping distance because it is a driver distraction, and the driver
may be holding the cigarette when something happens not have that hand on the wheel.
4. Increased tyre tread greatly reduces the braking distance of a car. Why do you think that cars are not all
fitted with thick, chunky, off-road tyres with huge treads?
Thick, chunky, off-road tyres with huge treads increase the friction between the tyre and the
road. Increased friction will mean that the engine has to do more work, hence fuel consumption
will increase. The ride quality will also be worse as the noise will be higher and the ride will be
more uncomfortable.
71
WJEC GCSE Additional Science Teacher’s Notes
19
Using radioactive decay
_ Radioactive decay (pages 211–213)______________
Questions
1. What are the three types of radioactive decay?
alpha (α), beta (β) and gamma () decay
2. What can ionising radiation do to living cells?
Damage, mutate or kill cells.
3. What is the half-life of a radioactive isotope?
Time taken for half the original amount of radioactive atoms to decay or the time taken for the
activity of a sample to halve.
4. After how many half-lives will the activity of a radioactive sample be about the same as natural
background activity?
About 5 half-lives.
5. Why is iridium-192 chosen to treat eye sarcoids on horses?
Iridium-192 is a beta emitter with a half-life of 74 days – long enough to be transferred from
the reactor where it is made, but short enough to be effectively used for treatment before it is
returned to the reactor.
6. How long will it take a sample of iridium-192 with an initial activity of 1200 Bq to reach an activity of
75 Bq? [Remember, the half-life of Ir-192 is 74 days.]
After 1 half-life: activity = 1200/2 = 600 Bq
After 2 half-lives: activity = 600/2 = 300 Bq
After 3 half-lives: activity = 300/2 = 150 Bq
After 4 half-lives: activity =150/2 = 75Bq
4 half-lives = 74 × 4 = 296 days
7. A sample of iridium-192 has an activity of 215 Bq, 296 days after it was removed from the nuclear
reactor that made it.
a
How many half-lives have elapsed in 296 days?
Number of half-lives = 296/74 = 4
b
What was the initial activity of the sample?
Initial activity = ((((215 × 2) × 2) × 2) × 2) = 215 × 24 = 3440 Bq
8. Table 19.1 shows the radioactive decay of a sample of iodine-131, a radioactive isotope sometimes
used to treat thyroid gland problems.
a
Plot a graph of activity (y-axis) against time (x-axis).
b
Draw a best-fit line (curve) through your points.
72
WJEC GCSE Additional Science Teacher’s Notes
c
Use your graph to measure the half-life of iodine-131.
PRACTICAL The radioactive decay of protactinium-234
(page 213)
Safety: If you are doing this experiment using a protactinium generator, then you must follow
the relevant Radioactivity Local Rules for your school and the relevant CLEAPSS guidance.
A data-logging GM counter substantially enhances this activity, as the activity can be displayed
in real-time as a graph.
_ Carbon dating (page 214)______________________
Questions
9. What is carbon dating?
Carbon dating is a scientific technique for determining the approximate age of an artefact that
contains once living matter using the half-life of the naturally occurring carbon-14 isotope.
10. Why do you think that dating dead organic materials over 60 000 years old is almost impossible using
carbon dating?
The half-life of carbon-14 is 5730 years – after 5 half-lives (= 28 650 years), the percentage of
carbon-14 left in the sample is very low, after 60 000 years it is so much lower that it cannot be
detected.
11. The Turin Shroud is a holy relic, reputedly the shroud used to wrap Jesus in after his crucifixion. The
shroud appears to have the image of a man ‘etched’ on one side of the cloth. In 1988, three
independent carbon-dating laboratories analysed fibres taken from the shroud and discovered that the
73
WJEC GCSE Additional Science Teacher’s Notes
samples studied contained just over 90% of the original amount of carbon-14. Use the carbon dating
graph in Figure 19.6 to estimate the age of the Turin Shroud.
From the graph, approximately 1/6 of a half-life has elapsed, so 5730/6 = 955 years
Sample was produced in 1988 – 955 = 1033AD
Discussion point
There is much debate about the authenticity of the Turin Shroud. Recent scientific studies have found that
while there is no evidence of any scientific forgery, and the origin of the image on the shroud is still
unknown, there is also a suggestion that the samples of the cloth examined in 1988 are not representative
of the whole shroud. What happens in this case? The carbon dating data indicates the shroud is a medieval
artefact. Is it possible to prove one way or another that the shroud is real, or a very, very elaborate and
clever hoax?
There are many websites on the net that will help to initiate debate on this topic. This would make
an excellent homework task: ‘What evidence is there that the Turin Shroud is a medieval fake?’
TASK Using radioactive materials (pages 215–19)
1. Which radioactive element from the table would you use for an RTG? Explain your answer.
Plutonium-238 is normally used for this application, but from the list on P215, an alpha
emitter with a half-life of hundreds of years would be suitable – americium-241.
2. Why do you think that RTGs are only used as the power supply on un-manned devices?
RTGs are very radioactive and produce too much radiation to be safe on a manned device.
3. Which radioactive elements would be suitable for use as a radioactive tracer? Explain your answer.
The tracer must be a gamma emitter (so that the radiation can escape the body) with a short
half-life (so that the radiation dose received by the patient is minimised) – technicium-99.
4. Why is it important that the radioactive tracer that is used has a very short half-life?
The tracer must have a short half-life so that the radiation dose received by the patient is
minimised.
5. For each of the following forms of radiotherapy suggest and explain which radioisotope(s) you would
choose:
a
external beam radiotherapy
A gamma emitter with a half-life measured in hundreds of years would be needed so
that the beam of gamma rays remained as constant as possible – Europium-152 or
Barium-133.
b
brachytherapy
A beta emitter with a half-life of tens of days would be suitable – iridium-192.
c
unsealed source radiotherapy
A beta emitter with a short half-life – iodine-131.
74
WJEC GCSE Additional Science Teacher’s Notes
6. Explain what safety precautions a specialist radiotherapy nurse would have to take if treating a
patient using external beam radiotherapy.
The safety precautions are:
 leave the room when the gamma beam is on
 observe patient through lead glass screen
 focus the beam carefully
 control beam exposure so dose is effective but minimised.
7. Which radioisotopes would you use for leak detection?
Gamma emitter with a short half-life is needed – technicium-99.
8. Why is it important that radiosotopes used in leak detection have short half-lives?
Half-life must be short to ensure that the dose received by the general public and the
operators is very small.
9. Why are beta sources used for thickness control applications?
The intensity of beta particles passing through the paper will be affected by the thickness of
the paper. No alpha particles would get through even the thinnest paper, and gamma rays
would be unaffected by the paper.
10. State with a reason which radioisotope you would choose for use in a thickness control machine.
How would you arrange this source under the sheet?
Strontium-90 would be a good source for a thickness detector as it is a beta emitter with a
suitable half-life where the intensity of the beta particle beam would not change
significantly from day to day. The source would be extended underneath and across the full
width of the paper so that the detector sampled the full width.
11. Why is it important that the Geiger counter is long enough to stretch across the whole sheet?
The Geiger counter needs to sample across the whole of the width of the sheet to ensure it is
an even thickness.
12. Which radioisotopes would you use for metal weld detection? Explain your answer.
A gamma emitter with a long half-life so that the gamma beam intensity did not change
significantly from day-to-day – Europium-152 or Barium-133.
13. What precautions would the operator need to take when analysing a metal weld?






Keep (very small) source in sealed lead container when not in use
Minimise time in use
Collimate beam (so it only goes in one direction)
Stand away from the beam when in use
Ensure no other people are in the way of the beam
Wear lead apron/tabard
14. Why would α and β radioisotopes be unsuitable for this application?
Alpha and beta radiation would not penetrate through the weld.
75
WJEC GCSE Additional Science Teacher’s Notes
15. Explain which radioisotopes you could use for a machine that sterilises medical instruments.
A gamma emitter with a long half-life so that the gamma beam intensity did not change
significantly from day-to-day – Europium-152 or Barium-133.
16. Why is it important that the sterilising machine is surrounded by a thick lead shield?
To minimise dose/exposure to the operators.
17. Explain why americium-241 would be a good choice for the radioisotope in a smoke detector.
It is an alpha emitter with a long half-life so that the beam intensity does not drop
significantly from day-to-day.
18. Why doesn’t a smoke alarm need a lead shield around it?
It is an alpha emitter and so the alpha particles are absorbed inside the detector by the walls
of the radioactive source holder and the plastic cover.
Discussion point
Some types of food are treated in the same way. Strawberries, onions, potatoes and spices can all be
sterilised in this way. By killing the bacteria on the food products they can have a substantially longer
shelf-life. Would you like to eat irradiated strawberries?
An interesting discussion pitting scientific understanding against irrational fear!
76
WJEC GCSE Additional Science Teacher’s Notes
20
Nuclear power?
Discussion point
There are lots of resources online that show the possible effects of the La Palma mega-tsunami. You might
like to try: www.guardian.co.uk/flash/cumbre_vieja_tsunami.swf
Both of these discussion points are based on student opinion.
1. Do you think that the potential for natural disaster outweighs the need for secure, large-scale, carbonneutral electricity?
You may like to point out that secure, large-scale, carbon neutral electricity need not
exclusively come from nuclear power.
2. Global warming or nuclear disaster – which is worse in your view?
Is it a choice between one or the other?
_Where does nuclear power come from? ____________
(pages 222–23)
Questions
1. Write nuclear equations for the following decays:
a
235
uranium-235, 92 U , also an alpha particle emitter, decaying into thorium-231,
235
231
92 U  90Th
b
231
90Th .
 42 He
14
14
carbon-14, 6 C , is a beta emitter, decaying into nitrogen-14, 7 N .
14
14
0
6 C  7 N  -1 e
2. Use a Periodic Table or a Table of Nuclides (try:
http://en.wikipedia.org/wiki/Table_of_nuclides_(complete)) to write nuclear equations to determine the
decay product of the following isotopes:
a
b
alpha emitters:
i
americium-241
241
237
4
95 Am  93 Np  2 He
ii
polonium-210
210
206
4
84 Po  82 Pb  2 He
iii radon-222
222
218
4
86 Rn  84 Po  2 He
iv radium-226
226
88 Ra
v
236
232
4
94 Pu  92 U  2 He
plutonium-236

222
86 Rn
 42 He
beta emitters:
i
hydrogen-3 (tritium)
3
3
0
1 H  2 He  -1 e
77
WJEC GCSE Additional Science Teacher’s Notes
ii
phosphorus-32
32
32
0
15 P  16 S  -1 e
iii nickel-63
63
63
28 Ni  29 Cu
iv strontium-90
90
90
0
38 Sr  39Y  -1 e
v
24
11 Na
sodium-24


0
-1 e
24
0
12 Mg  -1 e
_ Nuclear fission (pages 224–27)__________________
Discussion points
1. You do the maths: 1 atom of U-235 has a mass of 3.9 × 10–25 kg. How many atoms of U-235 are there
in 1 kg? If each atom’s nucleus can emit 3.2 × 10–11 J of heat energy, how much heat energy could 1 kg
of U-235 produce?
number of atoms 
1
 2.6  10 24
- 25
3.9  10
heat energy = 2.6 × 1024 × 3.2 × 10–11
E = 8.3 × 1013 J
2. Is nuclear power from fission worth it in terms of energy? 1 kg of U-235 could produce about 83 TJ
(83 × 1012 J) of energy. By comparison, 1 kg of best coal could produce 35 MJ (35 × 106 J). How much
coal would you have to burn to get the same amount of energy as 1 kg of uranium-235?
energy produced by 1 kg of uranium
energy produced by 1 kg of coal
6
= 2.4 × 10 kg (i.e. 2.4 million kg)
amount of coal needed 
3. Are there any other considerations when comparing coal and uranium?
For coal it is the environmental impacts of extraction and CO2 output.
For nuclear it is the environmental impact of radioactive waste (highly radioactive for hundreds
of millions of years).
Questions
3. Use a Periodic Table or a Table of Nuclides to write nuclear equations to summarise the following
fission reactions inside a nuclear fuel rod, occurring from the fission of uranium-235 from one neutron.
The fission products are:
a
xenon-140, strontium-94 and two neutrons
235
140
94
92 U  54 Xe  38 Sr
b
 201n
rubidium-90, caesium-144 and two neutrons
235
90
144
1
92 U  37 Rb  55 Cs  2 0 n
c
lanthanum-146, bromine-87 and three neutrons.
235
146
87
1
92 U  57 La  35 Br  3 0 n
49
WJEC GCSE Additional Science Teacher’s Notes
Discussion point
You can find out about how nuclear reactors work by searching online using key-words such as ‘nuclear
power plant’, ‘animation’ and ‘applet’. Your teacher may show you one of these. How is the heat energy
generated by the reactor transformed into electricity?
The heat from the reactor is used to heat water to make steam, which turns a turbine-generator –
the same as in a conventional power station.
Questions
4. What is the main fuel used in a nuclear reactor?
Uranium-235
5. What is a ‘chain reaction’?
The neutrons released from the fission of one U-235 atom can initiate the fission of other
U-235 atoms, and so on.
6. Why does a nuclear reactor need a moderator?
The fission of U-235 by neutrons requires the neutrons to be slow-moving – the moderator,
usually water, is used to slow the neutrons down increasing the likelihood of fission events.
7. How can a nuclear power station reactor be controlled?
Control rods, usually made of graphite or boron, absorb neutrons. Raising or lowering the
control rods controls the rate of fission and hence the power output of the reactor.
8. Why is the reactor encased inside a steel vessel surrounded by a thick concrete containment structure?
To minimise the escape of highly energetic and penetrating gamma rays (produced inside the
reactor) escaping into the local environment.
9. Why do spent fuel rods need to be stored under water in ponds within the containment structure?
The spent fuel rods are still highly radioactive and produce large amounts of heat. The water in
the ponds is used to cool the fuel rods.
10. Draw a flow chart showing how electricity is generated by nuclear fission in a nuclear power station.
Fission of
U-235
Heats water
producing steam
Steam turns turbine
which turns generator
Electricity produced and
delivered to the National
Grid
_ Is there another way? (pages 227–30)____________
Questions
11. What is nuclear fusion?
Nuclear fusion is the joining together of lighter nuclei to make heavier ones and during the
process emitting large amounts of energy.
12. Inside the core of the Sun, what are the particles involved with nuclear fusion?
Inside the Sun, hydrogen nuclei (protons) fuse together during the process of nuclear fusion.
49
WJEC GCSE Additional Science Teacher’s Notes
13. Why are high temperatures and pressures needed for nuclear fusion?
High temperatures and pressures are needed to ensure that enough protons get close enough for
the process of nuclear fusion to occur.
14. What are deuterium and tritium? How are they different to ‘normal’ hydrogen?
Deuterium and tritium are isotopes of hydrogen. They both contain a single proton (like normal
hydrogen) but a deuterium nucleus has an extra neutron, and tritium has two extra neutrons.
15. What is a plasma?
A plasma is an ionised gas.
16. How is the plasma of deuterium and tritium confined inside a tokamak reactor?
A toroidal (ring doughnut) shaped magnetic field confines the plasma inside the tokamak
reactor.
17. How are the high temperatures generated within a tokamak reactor?
The high temperatures are generated by passing huge electric currents through the plasma.
18. How could the energy of a nuclear fusion reactor be used to produce electricity?
The high kinetic energy of the neutrons emitted during the fusion process could be used to heat
water as the basis of electricity generation.
19. Why do nuclear fusion reactors need a lot of shielding?
Nuclear fusion reactors produce huge numbers of high energy neutrons which need to be
contained to prevent damage to the human operators.
Discussion point
Other rival nuclear fusion reactor designs (such as HiPER – the European High Power laser Energy
Research facility) would use high powered lasers to heat a small quantity of deuterium and tritium inside a
small spherical pellet. Such designs have been shown to work, producing small quantities of nuclear fusion.
The trick is to get a continuous feed of fusion fuel into the laser beams in a short enough time to sustain the
reaction. Use the internet to find out about nuclear fusion reactors that use lasers (the process is called
Inertial Confinement Fusion or ICF). How might it compare to tokamak based reactors?
Using a search engine with the key words ‘inertial confinement fusion’ will find many different
websites devoted to Laser ICF. Tokamak reactors currently represent the best ‘chance’ of
producing a commercially viable nuclear fusion reactor.
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