The reactants are zinc and hydrochloric acid. They contain:
2 H, 2 Cl and 1 Zn atoms.
The products are hydrogen and
zinc chloride. They contain:
2 H, 2 Cl and 1 Zn atoms.
H
Zn
S C I E N C E
H
Cl
H
Cl
H
Zn
Cl
Cl
work
EX P E R I M E N T
Making silver
Aim
To observe the formation of pure silver by a chemical reaction.
!
Materials
•
•
•
•
1 .4
15 cm of copper wire (Cu), sanded or scraped to remove outer layer
5 mL of silver nitrate solution (AgNO3)
pencil
test-tube
Safety
Contact with silver nitrate can stain skin and clothing. Wear laboratory coats and eye protection
during this experiment and report any spills to your teacher immediately. Complete an RAS before you start this activity. Alternatively, this experiment could be a teacher demonstration.
Method
1. Pour 5 mL of silver nitrate solution into a test-tube.
2. Make a coil of copper wire by winding it around a pencil.
3. Place the copper coil into the silver nitrate solution.
4. Observe the reaction.
Discussion
1. Describe the crystals formed. What could they consist of?
2. What happens to the solution? What causes this change?
3. Write a word equation for this reaction.
copper wire
test-tube
silver nitrate solution
Figure 1 .1 5
The experimental set-up to make pure silver.
Evaluation
Are you satisfied that you know what the products of this chemical reaction are? Did you encounter
any problems in completing your experiment? How could you overcome these problems?
Extension
Redesign this experiment so that the masses of the reactants and the products can be compared.
Always use the minimum amount of reactants. Do you think the mass of the test-tube and its
contents will vary over the course of the reaction? Discuss your ideas with your teacher.
Complete an RAS before you carry out your experiment.
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Did you work out that when copper and silver nitrate reacted in the
last experiment, crystals of silver and a solution of copper nitrate were
created? This reaction can be expressed as a word equation:
copper + silver nitrate → silver + copper nitrate
You can replace each part of the word equation by a chemical formula:
Cu + AgNO3 → Ag + Cu(NO3)2
Looking at both sides of this equation, you can see that it is not
balanced. Although the silver and copper are balanced, the nitrate ion
(NO3–) is not. To balance this equation, you need to add numbers in
front of some of the chemical formulae. You could start by putting
a 2 in front of the AgNO3 to balance the NO3– ions, but that would
cause the Ag+ ions to be unbalanced. Another 2 is therefore needed in
front of the Ag. After this trial and error, you have now balanced the
equation:
Cu + 2AgNO3 → 2Ag + Cu(NO3)2
Checking the number of atoms shows that there is one Cu, two Ag, two
N and six O atoms on both sides of the equation.
An equation cannot be balanced by changing any of the chemical
formulae. It can only be balanced by putting numbers in front of a
formula. Moreover, the balanced equation includes the symbols that
show the state of matter for each reactant and product.
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)
AgNO3
AgNO3
Synchrotron sources can be used
to look deep within the crystalline
structure of solids to a level we have
never before seen. By observing
patterns that the intense beam of
high energy synchrotron X-rays
make as they scatter from a source,
we are given information about
the inner structure of the source
being tested. One pharmaceutical
company put synchrotron science
to good use recently. The company
successfully argued that their own
patented top-selling drug had been
copied by a generic manufacturer.
Analysis using synchrotron light
revealed that the crystalline structure
of the patented drug and the
generic version were so identical
that the manufacturer producing the
generic version was ruled to have
been selling their drug illegally.
Ag
Cu(NO3)2
Ag
01
chapter
Cu
scif ile
chemical interactions
Balancing chemical equations
Figure 1 .1 6
A balanced equation.
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hydrogen
oxygen
Rules for writing balanced chemical equations
1 Write a word equation for the chemical reaction.
2Write a formula for each of the reactants and products. (Refer to
Table 1.1 if necessary.)
3Use numbers in front of the formulae to balance the numbers of
atoms on each side of the equation. (It helps to try to balance the
more complex compounds first.)
water
4Check each type of atom to make sure that the equation is
balanced.
electrodes
+–
power supply
Figure 1 .1 7
This apparatus can be used to decompose
water into hydrogen and oxygen gas.
scif ile
Atoms and molecules are so small
that they can’t easily be handled
singly or in small numbers. When
bundling atoms or molecules,
scientists use an amount called
a ‘mole’. A mole is a very large
number of atoms. For example,
1 mole of water has a mass of
18.0 g and consists of 6.02 × 1023
(602 000 000 000 000 000 000 000
molecules). It’s handy that you don’t
order soft drink by the mole!
S C I E N C E
5Include the symbols for the states of matter for the substances
involved.
You might find it useful to use a table to write and balance chemical
equations. For example, we could consider the reaction that occurs when
electricity is passed through water, as shown in Figure 1.17. The electric
current makes the water decompose into the products hydrogen and
oxygen gas. Table 1.5 shows how we can balance the chemical equation
for this reaction. Before you read it, have a go yourself!
Table 1.5 Balancing a chemical equation
Reactants
Products
Word equation
water
→ hydrogen + oxygen
Chemical formulae
H2O → H2 + O2
Use numbers in front of
formulae to balance atoms
2H2O → 2H2 + O2
Checking
4 × H, 2 × O
Balanced equation
2H2O(l) 4 × H, 2 × O
→ 2H2(g) + O2(g)
work
The X factor
1. Working with a partner, examine the following three chemical equations.
A c t i v i t y 1 .5
In each case, see if you can choose the correct value for x (from the options in
brackets) to balance each equation.
(a) H2(g) + Cl2(g) → xHCl(g) (x = 2, 3 or 4)
(b) AgNO3(aq) + NaCl(aq) → xAgCl(s) + NaNO3(aq) (x = 1, 2 or 3)
(c) xNaOH(aq) + H2SO4(aq) → Na2SO4(aq) + xH2O(l) (x = 1, 2 or 4)
2. In answering part (a) above, explain why you could certainly not rewrite the final product to be H2Cl2.
Draw a diagram to assist your explanation of why answering in this way could cause your science
teacher to pull their hair out!
3. Complete a PMI chart for this activity.
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S C I E N C E
work
EX P E R I M E N T
Swapping ions
Aim
To observe a chemical reaction and to write a balanced chemical equation.
1 .6
!
Materials
• barium nitrate solution (Ba(NO3)2)
• copper sulfate solution (CuSO4)
• test-tubes
barium
nitrate
copper
sulfate
Method
1. Pour about 1 cm depth of barium nitrate solution into
one test-tube and about 1 cm depth of copper sulfate
solution into the other.
2. Pour the contents of the test-tubes into a third test-tube.
3. Allow the mixture to settle.
4. Record your observations.
precipitate
barium
sulfate
Figure 1 .1 8
A precipitate of barium sulfate
is formed in this reaction.
Discussion
In this reaction, the ions from one substance combine with
the ions of the other to form a solid.
1. List which ions are present in the reactants used in this
experiment.
2. Now write a word equation for this reaction, showing
how the ions swap from one substance to the other.
3. What product remains dissolved in the clear solution?
How could you obtain a solid product from this solution?
4. Write a balanced chemical equation for this reaction.
chemical interactions
Barium nitrate and copper sulfate are poisonous and can be
harmful if inhaled. Handle them with care, and wash your hands
thoroughly after using them. Complete an RAS before you start
this activity.
test-tube
01
chapter
test-tube
Safety
Evaluation
Can you be certain that your experiment was a success? Suggest a way that you could verify your
result as correct and not the product of unclean glassware or contaminated chemical reactants.
questions 1.2
1. What is the law of conservation of mass?
Write this law in a simple form aimed at a
Year 7 student.
2. Lauren conducts an experiment where she
weighs four icy-pole sticks, burns them in a
metal tin and carefully weighs the ashes that
result. How will the mass of the ashes compare
with that of the original ice-cream sticks? Explain
the difference in the two masses.
3. Write a word equation and a formula equation
for each of the following.
(a)Silver nitrate and sodium chloride solutions
were added together and solid silver
chloride formed, as well as a solution of
sodium nitrate.
(b)If solid copper(II) carbonate is heated,
carbon dioxide gas is given off and
copper(II) oxide remains.
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weighs it and heats it in a crucible over a Bunsen
burner, as shown in Figure 1.19. The product is a
white powder, which has a mass greater than the
original magnesium metal. Where has the extra
mass come from? Write a word equation for this
reaction.
crucible and lid
magnesium
ribbon
gauze mat
tripod
8. What does Figure 1.20 tell us about the total
mass of reactants and products at any time
during a chemical reaction?
reactants
Mass
4. Giovanni takes a piece of magnesium ribbon,
products
Bunsen burner
Time
Figure 1 . 2 0
This graph indicates how the masses of the reactants and
products change during a chemical reaction.
Figure 1 .1 9
Giovanni’s experimental set-up.
5. Which of the following reactions are not
balanced? Explain why.
(a) H2(g) + O2(g) → H2O(l)
(b) N2(g) + 3H2(g) → NH3(g)
(c) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
(d) Mg(s) + O2(g) → MgO(s)
6. You are a tiny atom of barium. Happy with your
friends, the hydroxides, you undergo a saga of
heart-wrenching separation, but eventually find
soul mates once more. Write a story or role-play
about your ordeal.
CuCl2(aq) + Ba(OH)2(aq) → BaCl2(aq) + Cu(OH)2(s)
7. Using the rules that you have learnt, balance the
following equations.
(a) Fe(s) + HCl(aq) → FeCl2(s) + H2(g)
(b) Na(s) + Cl2(g) → NaCl(s)
(c) CH4(g) + O2(g) → CO2(g) + H2O(g)
(d) CO(g) + O2(g) → CO2(g)
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9. Write balanced equations for each of the following
reactions.
(a)If a mixture of carbon and copper oxide is
heated, solid copper is produced as well as
carbon dioxide.
(b)Sulfur trioxide can be produced by burning
sulfur dioxide in oxygen.
(c)Water, ammonia (NH3) and carbon dioxide
are produced when solid ammonium
carbonate decomposes.
(d)Cane sugar (C12H22O11) can be decomposed
to give water and carbon.
10. Balance these equations and write sentence
descriptions for each reaction.
(a) NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l)
(b)CuCO3(s) + HCl(aq) → CuCl2(aq) + H2O(l) + CO2(g)
11. Using a format of your choice, design a presentation
of rules for writing balanced chemical equations,
along with an example. Deliver your presentation to
your class with illustrations. It could be presented
orally, as a written document or by electronic media.
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1. 3 Types of chemical
reactions
There are various ways that chemical reactions can be grouped
together. Some reactions use up energy and some give off energy.
Some reactions have a larger number of reactants than products while
others have more products than reactants. Other reactions have the
same number of reactants as products but ions are swapped around.
Your understanding of chemical equations will help you to be able to
identify some different types of reactions.
EX P E R I M E N T
Pulling compounds apart
Safety
To avoid bromothymol blue being ‘sucked back’ into the first test-tube, ensure that
once a colour change has been observed, the bromothymol blue test-tube is removed
before the heating flame is turned off. Complete an RAS before you start this activity.
!
Aim
To observe a chemical reaction in which carbon dioxide gas is produced.
Materials
•
•
•
•
copper carbonate powder (CuCO3)
2 test-tubes
delivery tube
clamp
•
•
•
•
bromothymol blue
one-holed stopper
retort stand
Bunsen burner
Method
1. Set up the apparatus shown in Figure 1.21, with
1–2 cm depth of copper carbonate in one test-tube
and 4–5 cm depth of bromothymol blue in the other.
2. Carefully heat the copper carbonate and note any
changes you observe.
3. Allow any gas given off to bubble through the
bromothymol blue.
4. Once a colour change is observed in the
bromothymol blue, remove this test-tube from
the delivery tube.
5. Turn off the Bunsen burner and record your
observations.
01
copper
carbonate
Bunsen
burner
1 .7
chemical interactions
work
retort
stand
bromothymol
blue
chapter
S C I E N C E
Figure 1 . 2 1
The experimental set-up.
Discussion
1. Given that bromothymol blue turns yellow in the presence of carbon dioxide gas, was the gas
given off carbon dioxide?
2. What changes in the copper carbonate could be observed?
3. What elements could the remaining solid consist of?
4. Why was the test-tube of bromothymol blue removed before the heating flame was turned
off? Explain what could have happened, and why.
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Conclusion
1. Write a statement that summarises the chemical reaction that has occurred.
2. Explain how you can use your knowledge of chemical reactions to predict the make-up of the
solid that is left over. If there was no such thing as the law of conservation of mass, do you
think this would be possible?
Evaluation
Did you have any problems with observing or recording changes? If so, suggest improvements in
the method to overcome these problems.
Extension
In a fume cupboard and using protective clothing, your teacher may take some of the remaining
solid and add concentrated sulfuric acid. Try to explain the changes that are observed.
scif ile
A sparkler is made up of a mixture
of chemicals that is coated on a
wire. The sparkler is designed to
burn relatively slowly, compared
with a firecracker that explodes
rapidly. Some metals, such as
aluminium, iron, zinc or magnesium,
can be used to produce bright
sparks. A fuel is required, like sulfur
or charcoal, and an oxidiser is used
to produce oxygen to keep the
sparkler burning. Such an oxidiser
undergoes a decomposition
reaction to produce oxygen.
One oxidiser that may be used is
potassium nitrate. This decomposes
as follows:
Decomposition reactions
During a decomposition reaction, a single substance is broken down
into simpler compounds or elements. There is one reacting substance
and two or more product substances.
In Science @ work 1.7 you conducted a decomposition reaction in
which copper carbonate decomposed to release carbon dioxide and left
the solid copper oxide:
heat
copper carbonate
copper oxide + carbon dioxide
CuCO3(s)
heat
CuO(s) + CO2(g)
2KNO3 → 2KNO + O2
The oxygen produced here keeps
that sparkler sparkling!
Figure 1 . 22
Sparklers consist of a chemical mixture
that is coated to a stick that is ignited.
Part of this mixture consists of an oxidiser
that decomposes to produce oxygen.
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S C I E N C E
work
Cooking with gas!
In this experiment you will explore a common decomposition reaction that
has great importance—without it, our cakes would not rise! In the kitchen,
ingredients are used instead of ‘reactants’, a recipe instead of a ‘method’,
and the ‘products’ are hopefully referred to as a culinary delight!
EX P E R I M E N T
1 .8
!
Warning
If possible, carry out this experiment in a home economics kitchen. If prepared in
the laboratory, these scones should not be eaten as equipment could be contaminated
from previous experiments.
Safety
To observe the results of chemical changes that take place when cooking baked foods,
like scones and cakes.
Materials
•
•
•
•
•
•
•
150 mL plain flour
30 mL milk
bicarbonate of soda (sodium hydrogen carbonate or sodium bicarbonate)
three 100 mL beakers
stirring rod
metal lid or aluminium pie tray
electric hotplate or Bunsen burner with tripod and gauze mat
Method
1. In each of the three beakers, carefully measure equal quantities of plain flour to the 50 mL
mark on the beaker.
2. To the first beaker add, while stirring, a small quantity of tap-water at a time until the flour just
holds together. The mixture should be able to be pressed together into a small scone.
3. To the second beaker, add approximately half a teaspoon of bicarbonate of soda and enough
water to produce a scone similar to the first.
4. To the third beaker, add approximately half a teaspoon of bicarbonate of soda and enough
milk to make a small scone.
5. Ensure that each scone contains a similar amount of liquid. Press the scone down until it is
no more than 1 cm thick. Make each scone a similar size and shape.
6. Place the scones on the metal lid on top of an electric hotplate or over a Bunsen burner, and
heat the scone very gently for about 15 minutes. (Alternatively use an oven if one is available.)
7 . Remove the scones from the heat and allow them to cool.
8. Record your observations of the appearance of the scones after cooking. Once cooled,
carefully break each one open and note the appearance inside the scones.
01
chapter
Aim
chemical interactions
• Complete an RAS before you start this activity.
• Heating apparatus should be used carefully to avoid burns.
Discussion
1. Which scone is the smallest? What do you note about its texture inside that has caused it to
be the smallest?
2. Which scone is the largest? What do you note about its texture inside that has caused it to
be the largest?
3. Which scone appears most edible? Why?
4. Given that the chemical formula of bicarbonate of soda is NaHCO3 and that this decomposes
to carbon dioxide, water and sodium carbonate (Na2CO3), write a balanced chemical
equation for this decomposition reaction.
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Conclusion
Comment on how the decomposition of bicarbonate of soda assists in making lighter scones.
Evaluation
Did you feel like a culinary success? List any problems that you needed to overcome in your
cooking experience. If you were to repeat this activity, would you make any changes to your
method? Explain.
S C I E N C E
work
On the rise
Using Science @ work 1.8 as a starting point, design an
experimental investigation into ways of making baked
goods rise. Cooks use other acids besides milk to react
with sodium hydrogen carbonate and produce carbon
dioxide. These include cream of tartar (tartaric acid) and
citric acid. You could start with some library research into
the chemical structure of these acids, where they come
from and how they are used. Then design an experimental
investigation using various amounts of acids and sodium
hydrogen carbonate to find the best conditions for making
baked items—and get cooking! Include an RAS in your
design. Write a scientific report on your work or create a
presentation to reveal your findings to your class.
i n v e st i g at
i o n 1 .9
Figure 1 . 23
Too much of one reactant can have unexpected results!
Synthesis reactions
Synthesis reactions are sometimes also known as combination
reactions because they involve several substances combining to give
a new substance. There are more reacting substances than product
substances.
Most metals, if exposed to air, will react with oxygen:
zinc + oxygen → zinc oxide
2Zn(s) + O2(g) → 2ZnO(s)
This is a synthesis reaction. Two substances (zinc and oxygen)
combine to give one new substance (zinc oxide). Coal (carbon) also
reacts with oxygen during combustion (burning). Not only
is carbon dioxide produced, but energy is also released
carbon + oxygen → carbon dioxide
C(s) + O2(g) → CO2(g)
Figure 1 . 2 4
Living things make use of synthesis reactions. Plants take simple substances,
such as water, nitrogen, carbon dioxide and oxygen, and produce large complex
molecules, such as sugars, other carbohydrates and proteins which then can be
used as food by animals.
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Single replacement reactions
A single replacement reaction involves removing one element or
group of elements and replacing them with another element or group
of elements.
In Science @ work 1.4 you observed the silver crystals formed
during a single replacement reaction:
copper + silver nitrate → silver + copper nitrate
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)
The silver in silver nitrate is replaced by copper. Copper nitrate is
formed as well as crystals of pure silver.
Sometimes when two compounds react, they totally swap ions. Two
new compounds are formed. Instead of one element or group of
elements being replaced, two lots are replaced. This is called a double
replacement reaction.
You observed this type of reaction in Science @ work 1.6. This is
called swapping ions because it is a double replacement reaction:
copper sulfate + barium nitrate → copper nitrate + barium sulfate
Figure 1 . 2 5
Magnesium metal burns in oxygen
with an intense white flame. This is an
example of a synthesis reaction. Can you
work out an equation for this reaction?
Ba(NO3)2 (aq) + CuSO4(aq) → BaSO4(s) + Cu(NO3)2(aq)
In this experiment, an insoluble compound (BaSO4) was formed and
appeared as a solid that settled out of solution. The insoluble barium
sulfate is known as a precipitate. Reactions that have precipitates as
their products are known as precipitation reactions.
chemical interactions
Double replacement reactions
chapter
01
Figure 1 . 26
Now that you know what a single replacement reaction is, can you guess what a double
replacement reaction is? The reaction between potassium iodide solution and lead nitrate
solution is a spectacular example of a double replacement reaction.
S C I E N C E
work
Identifying reactions
Aim
To observe and identify some different types of chemical reactions.
EX P E R I M E N T
1 .1 0
!
Part A: Making chalk
Materials
•
•
•
•
•
two 250 mL beakers
• distilled water
retort stand and ring
• filter funnel
filter paper
• stirring rod
2.5 g sodium carbonate powder (Na2CO3)
20 mL of 1.0 M calcium chloride solution (CaCl2)
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Method
1. Place the sodium carbonate into a beaker and
retort stand
filter paper
dissolve it in about 20 mL of distilled water.
2. To this solution add 20 mL of calcium chloride
solution. Mix the solutions by swirling the beaker.
3. Filter the mixture using the apparatus in Figure 1.27.
4. Pour two lots of 10 mL of distilled water over the
product to wash it.
5. Place the filter paper in a beaker to dry.
filter funnel
ring
beaker
Discussion
1. Describe the chalk produced during this experiment.
2. If chalk is calcium carbonate, what other product is formed?
3. Write a word equation and balanced equation for this reaction.
4. What type of reaction is this?
Figure 1 . 2 7
The experimental set-up
for making chalk.
Part B: A more complex reaction
Sometimes a reaction may occur with a couple of stages, incorporating a combination of the
reaction types that we have studied. This is such a reaction.
Safety
Copper carbonate is a poison. Treat it with care and wash your hands thoroughly after using it.
Materials
• two test-tubes
• rubber stopper and delivery tube
• 2 M sulfuric acid (H2SO4)
• test-tube rack
• copper carbonate powder (CuCO3)
• limewater (Ca(OH)2)
Method
1. Pour 4–5 cm depth of limewater into a test-tube.
2. In the second test-tube, place 1–2 cm depth of copper carbonate and add 5 mL of sulfuric acid.
3. Quickly insert the rubber stopper and delivery tube into this second test-tube, and direct the
delivery tube into the limewater that you poured into the first test-tube.
4. Record any changes to the limewater.
Discussion
1. This reaction occurs in two stages. Write the reactant down for the chemicals that were added
together in the second test-tube. Looking at these reactants, write down the products you
would expect to find if a double replacement reaction occurred. Can you balance this equation?
2. One of the products of this reaction is hydrogen carbonate. Remembering back to your work in
making scones in Science @ work 1.8, what type of reaction would you expect to occur now?
3. Given that limewater turns cloudy in the presence of carbon dioxide gas, did you detect the
presence of carbon dioxide gas in the limewater?
4. What other products would you expect to form in this reaction?
5. Write a balanced chemical equation for this chemical reaction.
Evaluation
Were you satisfied with the way you and your partner completed this experiment? List any
stages that could have been dangerous without full concentration. Make a list of possible
hazards and ways to avoid each one.
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