Chemical Change – Changing Form
Lessons 1 and 2
Prior knowledge
What is a chemical change?
Chemical change – Introduction
Chemical changes occur when objects or substances are changed or altered. In a chemical change,
particles of the original materials collide with one another. Some chemical reactions (called
exothermic reactions) give out heat and may become hot enough to cause certain chemicals to also
undergo a change in state. For example, in the case of reactiuons in water-based solutions, bubbles
may not necessarily be newly produced gas but instead water vapor. Chemical change is a change
which is usually irreversible.
Examples of chemical changes:
 Burning
 Decomposition
 Neutralisation (Reacting an acid with a base, resulting in water and a salt)
 Photosynthesis – a process in which carbon dioxide and water are changed
into sugars by plants
 Cracking heavy hydrocarbons to create lighter hydrocarbons (part of the process
of refining oil)
 Cooking examples: cake, pancakes, and eggs/bacon
 Oxidation examples: rust or tarnishing
 Ripening examples: bananas, tomatoes or potatoes
How can you tell whether a change is a chemical change?
Colour
As in the case of autumn leaves, a change in colour is a clue to indicate a
chemical change. When you cut an apple open, it starts to turn brown very
quickly and different varieties go brown quicker than others. This is
because a chemical change occurs when food spoils.
Energy
Another sign of a chemical change is the release or gain of energy by an
object. Many substances absorb energy to undergo a chemical change.
Energy is absorbed during the chemical change involved in cooking, like
baking a cake.
Odour
It only takes one experience with a rotten egg to learn that they smell different from fresh
eggs. When eggs and food spoil, they undergo a chemical change. The change in odour is the clue
to the chemical change.
Gases or solids
The formation of a gas is another clue to chemical changes. The bubbles of gas that form when an
antacid tablet is dropped into water, is an example of a chemical change. Another clue that a
chemical change has occurred is the formation of a solid. A solid that separates out of solution
during a chemical change is called a precipitate.
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Chemical Reactions
Chemical Changes are also called Chemical Reactions. Chemical reactions involve combining
different substances. The chemical reaction produces a new substance with new and different
physical and chemical properties. Matter is never destroyed or created in chemical reactions. The
particles of one substance are rearranged to form a new substance. The same number of atoms that
exist before the reaction, exist after the reaction.
Skills focus
Observing and measuring
Observation is a really important skill for the scientist. The ability to see what is really happening
rather than seeing what you expect to see can be difficult. It’s a good idea to give pupils observation
exercises to help them to improve this skill.
A good example of an observation exercise is to get them to describe what happens when a match is
struck. The first time they see it, they will see the flare of the flame as it is struck, the yellow flame
and the match turns to black. If you repeat it, asking them to observe every little detail including
sounds and smells, the list they come up with is enormous.
Pupils should be able to choose and use simple scientific equipment and materials appropriately and
take action to the control risks involved in their use. They need to make systematic observations and
accurate measurements using appropriate equipment, including the use of ICT for data logging. In
their investigations, pupils should check their observations and measurements by repeating them
where appropriate to ensure that they are reliable.
Recording data
Pupils should demonstrate their ability to use a wide range of methods, including diagrams,
drawings, tables, bar charts, photographs, video clips, voice recordings, line graphs and ICT, to
communicate data in an appropriate and systematic manner. Pupils will need explicit skill teaching in
order to construct tables, charts and graphs well. They also need practise in choosing the most
appropriate method to show their results to analyse and evaluate their evidence.
The way data is recorded often depends on the type of data. Measurements are often tabulated
before they are put on a graph, pie chart or bar-chart. A bar chart or pie chart is used to show
categoric and discrete variables. Continuous variable are show continuous variable Observations
which are made can be recorded by photograph, picture or diagram. Events may be recorded using
video or sound recording. (For more examples, see the data support sheet, on the website).
Lessons are designed to be flexible, and can be organised to suit your class and timetable. Our
suggested plan is to spend one lesson delivering the theory and demonstration. The website has
lesson plans and video demonstrations to serve as reminders. Time can then also be spent on the
skills focus, i.e. planning, collecting data or interpreting data. Children can discuss predictions,
questions that could be tested, variables and possible outcomes.
The following week time can be taken to revisit the scientific knowledge and children have the
opportunity to plan their own investigation. There is then time to work in pairs to carry out the
experiment and evaluate their findings and observations at the end of the lesson.
Each lesson plan has homework suggestions and links to further studies.
Differentiation is not stated by year groups as classes vary from year to year, cohort to cohort and
school to school. We state our aims for most children and then for some. This means that every
demonstration and investigation has been chosen because any KS2 child can access it at some level.
The level of understanding, language used, ability to relate concepts and investigate are the skills
which develop as the child learns.
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Changing Form
Lesson Objectives
Choose from:
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Understand that chemical reactions cause a change.
Know that a chemical change is often an irreversible change.
Carry out an investigation that will produce valid data.
Essential Knowledge/ Science Explained - for teachers
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Different salts produce different coloured flames (fireworks are a typical example). In this case the boric acid
burns with a green flame. Lithium salts burn with a red flame, barium salts with pale green flame and calcium
salts with a brick red flame. Other salt produce different colours.
Hydrogel is an interesting polymer as well as an example of a smart material. Hydrogels are smart materials
because their molecules change shape when there is a change in their environment – in this case, the change in
the concentration of ions.
Hydrogels are polymers that can retain many times their own weight in water. The polymer molecules have
sites along their length that attract and trap water molecules. Trapping water molecules remove them from the
solution making the solution more concentrated
and more viscous (thicker).
The polymer is in equilibrium with the water
around it, but that equilibrium can be disturbed in
a number of ways:
Adding salt prevents the sites on the polymer
molecules that attract and trap water molecules and so the hydrogel gives up the trapped water, and the
solution becomes less viscous. Different types of hydrogel can be made that are sensitive to different conditions
such as pH, temperatures and ionic concentrations.
The hydrogels in this practical activity are sensitive to salt concentration, but are not affected much by changes
to pH. However, they do lend themselves very well to a range of investigative practical work. For example, their
volume in different amounts of water or in different salt concentrations can be measured.
More information on hydrogels can be found using the link.
http://www.gcsescience.com/o70.htm
Common Misconceptions
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Particles can change form or shape.
Molecules are indivisible.
Molecules of solids are bigger than those of liquids or gases.
The space between molecules contains air.
Solids, liquids and gases are ‘different’ substances.
Chemical reactions are simple mixing of substances.
Children often associate gases with the use and function of objects, like footballs and tyres.
Termly Scientific Skills Development Focus: Recording and Analysis of Scientific Data and
Observations
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Collecting and presenting scientific observations in a way that can be analysed.
Creating graphs and charts of the data.
Analysing data the data obtained from the experiment and determining whether or not it proves or disproves the
prediction.
Opportunities should be given throughout the lesson for children to use and develop their knowledge of planning
investigations, through questioning and discussions on questions to investigate, making predictions and suggesting
dependent and independent variables.
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Cross curricular links
Literacy
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Numeracy
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Other subjects
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The green fire could be used as a stimulus for creative writing – poetry.eg. Green is
the colour of… or personification, eg. The fingers of the flame grasped…
Begin a science glossary for the class/younger children.
Use the green flame demo as a stimulus for adjectives/adverbs or
synonyms/antonyms.
Write an instructional text for another class to use to carry out the nappy
investigation.
Use tables and graphs to record data collected from the nappy investigation.
Calculate averages from other children’s data.
Find patterns/is there a ratio between the amounts of water added to the
hydrogel before it becomes saturated?
Lots of opportunities for measuring capacity during the investigations.
Green fire may inspire some artwork around mythical beasts/fantasy creatures.
Video of Japanese artists drawing dragons in a single stroke http://www.businessinsider.com/kousyuuya-studios-dragon-art-2014-8?IR=T
New inventions. Watch the video to see how has used hydrogels to solve his
problem. http://www.abc.net.au/tv/newinventors/txt/s2494979.htm
What problems are there in class and what could children invent to solve them?
Giving out books, collecting pencil sharpening’s, lost pens are all common
classroom issues.
Preparation
 Organise practical and delivery and set up of equipment in classroom.
 You may require extra help in the classroom such as a teaching assistant as there is a lot to get through.
Suggested Lesson Organisation
 Set up and show the demonstration, then explain and introduce the investigations they are to be involved in.
 Get the pupils into pairs and get each pair to collect the apparatus and chemicals they will need to carry out the
investigation.
 It is probably best for pupils to do the hair gel experiment first as that is quite quick and easy to do.
Prior Discussion
What is a chemical change?
Engage children in a discussion of what they can recall from the Particle Theory and Energy units.
List some of the changes that may occur when a chemical reaction has taken place.
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Heat
Colour
Smell
Size
Change of state
Can children give examples for each one? Or examples from the real world, for example in cooking.
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Teacher Demonstration
Demonstration - Green fire
See http://chemistry.about.com/od/funfireprojects/a/greenfire.htm
Health & Safety: The teacher must wear eye protection.
This may need to be performed outside if there are smoke alarms in the room. If performing inside use the safety
screen.
For one demonstration, you will need:
 Safety glasses
 Boric acid
 Spatula
 Methanol (methyl alcohol)
 Heatproof mat
 Tin lid/Evaporating basin
 Matches
 Safety screen
Procedure
 Discuss with the class what may happen when you add a powder to a liquid. They may suggest it dissolves, it sinks
etc. This can lead to a discussion on whether a new material is made or it is a reversible change.
 Take a couple of spatulas of the boric acid and place them in a beaker. Stir with 20 ml of methanol and then pour
half into the tin lid.
 Most of the boric acid will dissolve but there will be some left in the bottom. This won’t matter as it won’t affect the
experiment.
 Place the tin lid on the heatproof mat and place the safety screen in front. The children should stand about a metre
away from the front of it.
 Light the methanol with a match and behold! Green fire!
This is a quick and easy experiment that produces an exciting result. The residue left in the tin lid can be flushed down
the sink once the methanol has completely burned off.
Possible Questions/ Suggestions for discussion
There is a practical that they will get involved with at high school, if they choose to take chemistry, called ‘Flame Tests’
and that will go into more detail regarding what colour flames are produced when different salts are burned. However in
the meantime check out the link below for the full list of salts and the colours they give.
http://en.wikipedia.org/wiki/Flame_test
Have children seen this anywhere before?
It is using mixtures of these salts in the manufacture of fireworks that create the spectacular colours. Magnesium metal
burns with a brilliant white light which you get in a sparkler and it is a major component in all fireworks.
Children’s Investigation
Hydrogels: Nappies and Hair gels.
In this activity students investigate hydrogels: polymeric smart materials. They are found in many commonly available
products including disposable nappies and cheap hair gel. http://www.practicalchemistry.org/experiments/experimentswith-hydrogels-hair-gel-and-disposable-nappies,143,EX.html
Health & safety – Safety glasses must be worn by all pupils and teacher throughout. Safety gloves should be worn for
man-handling the nappies.
Each group will need:
 100 ml measuring cylinder
 800 ml tri-pour beaker
 Plastic stirrer
 1 nappy
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Plastic bowl/tray
Sodium chloride (salt)
Plastic spoon
Water
Petri dish
Hair gel
Paper towels
Safety glasses
Disposable gloves
Few drops of Food colouring - (Dilute to colour the water – to ensure a nice urine colour)
Procedure - Disposable nappy
1. Cut the middle section out of the nappy – the thicker piece that is designed to absorb the urine. Discard the other
piece.
2. Make sure the bowl is completely dry - wipe it with a paper towel if necessary. Any moisture in the tub stops the
experiment from working properly.
3. Put the centre piece of the nappy into the bowl and gently take it apart. Small white grains should start coming away
and this is what you are trying to collect. Keep gently pulling the nappy apart until you have collected as many of the
grains as you can. Do not do this roughly or you will lose your product and put a lot of dust and fluff into the air.
Avoid breathing in any of the dust which is sodium polyacrylate (Low hazard but eye irritant).
4. Remove and dispose of all the fluff and other parts of the nappy, keeping the grains in the bottom of the bowl. They
are heavier and fall to the bottom, which makes it easier to separate them out.
5. Estimate the volume of the grains.
6. Pour them into the large beaker and add about 100 ml of coloured water. Stir. Keep adding water until no more can
be absorbed and stir between each addition. Estimate the final volume of the hydrogel.
7. Add a dessertspoonful of salt and stir.
Procedure - Hair gel
 Put a blob of hair gel onto the petri dish lid. (A large spatula full is fine).
 Gently sprinkle a spatula full of salt, over the hair gel.
 Observe what happens.
Possible Questions/ Suggestions for discussion
Students should make detailed notes on their experiments, using recording sheets as necessary, noting changes in
volume, colour and any other observations. Some expected observations could include:
Hair gel
The hair gel shrinks in size very quickly when the salt is added. After a couple of minutes all that is left is some liquid in
the petri dish.
Disposable nappy
About 10 ml of hydrogel can be extracted from the nappy core. (Exactly how much depends on the make and the size of
the nappy.) The hydrogel swells up extremely quickly. It absorbs about 500 ml of distilled water giving a very viscous
mixture. When salt is added, the viscosity immediately reduces and the mixture is easier to stir. The hydrogel releases
the water and settles on the bottom of the beaker.
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What explanations can children give for what they have seen?
Can they make connection between the two investigations?
Can they make comparisons between the two investigations?
Name the variables.
Can pupils think of another measurement they could have taken?
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Learning Outcomes
All children should
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Practise making predictions and controlling variables.
Be able to carry out an investigation which produces reliable data.
Record data in a novel way.
Approach practical work in a safe and appropriate manner.
Know why not all flames are orange and the colour of the flame is affected
by the chemicals which are burning.
 Name some chemical changes.
Some children could
A few children could
 Practise independently identifying a variable to test in an experiment.
 Realise there are often problems with investigations and scientists need to
minimize these.
 Identify common chemical changes in everyday life.
 State clearly that their results are valid because of the various factors they
controlled.
 Analyse data and suggest an alternative way of ensuring its validity.
 Know that Hydrogels are classed as smart materials because they change
shape when there is a change in their environment – this determines their
ability to absorb.
 Make a list of as many different types of “smart materials” that you can
find. What are their special qualities that make them ‘smart’?
 Take one of the materials you have found and devise an experiment to test
its unique properties. (Hint: The internet should give you all the
information).
Plenary/Review including Skills Progression focus: Recording and analysis of scientific data and
observations
What are the unique properties of the hydrogel?
Where else could this ability to absorb vast quantities of water be used?
What are the advantages and disadvantages of using such a product?
Useful websites
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Hydrogel ball video: https://www.youtube.com/watch?v=IPK2m0qRZx4
Green fire tornado video: https://www.youtube.com/watch?v=v6IbKE8hmiQ
Simple chemical reactions explained: http://www.chem4kids.com/files/react_intro.html
Science quizzes – to model or research: http://www.sciencekids.co.nz/quizzes.html
Lovely PowerPoint on simple chemical reactions – some revision: https://www.tes.co.uk/teaching-resource/7fsimple-chemical-reactions-for-sen-6168561
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NOTES:
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