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Chemical reactions revisited
Read
You already know that when some chemicals touch each other
they can react to make new chemicals. This is called a chemical
reaction. If a chemical reaction happens a new substance is
always made and we might see:




A change in colour - for example a rusting car
A gas being made –
for example a rotting
egg
A solid being made –
for example milk
turning sour
Heat or light being
given out or used up – for example any kind of
burning eg. coal, wood, petrol, paper etc.
Sometimes a solid is made when two clear solutions are mixed.
This solid has a special name – it is called a precipitate.
Your teacher may show you a video of chemical reactions (SS11)
Write a heading and try the work below.
1. In a chemical reaction a n___ s___________ is always
made.
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2. Give an example of
a) a reaction where you might see a colour change is
___________________________
b) a reaction where you might notice a gas being made is
___________________________
c) a reaction where a solid forms from a liquid but not by
freezing is _____________________________.
d) a reaction that gives out heat is _______________
_____________.
3. The special name for a solid that is made when two solutions
are mixed is a P___________
4. Complete the table below while doing experiment 1.20
Substances added what I saw
together
Indigestion
powder + vinegar
Sulphuric acid +
copper
Sodium carbonate
+ cobalt chloride
Copper sulphate +
zinc
Sulphuric acid +
magnesium
Barium chloride +
sodium sulphate
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chemical
reaction? (Y/N)
Telling if a gas has been made
Read
It is sometimes difficult to tell if a gas has been made in a
reaction but we know a gas has been made if:




We see bubbles made in a
solution.
We can see it.
We can smell it.
We can use a test for it.
Try the work below.
1. Make a list of the 4 ways that we can tell if a gas has been
made in a reaction.
(i)
(ii)
(iii)
(iv)
____________________________
____________________________
____________________________
____________________________
2. Collect experiment card 1.21, do the experiments and fill in
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your table. NB Use pyrex test tubes for heating.
What I heated
what happened
chemical reaction?
3.In one of the experiments the glowing splint relit. This tells
me that the gas made was oxygen/nitrogen.
Telling if there is an energy change
Read
Sometimes the only way to tell if a chemical reaction has
happened is if there is an energy change. We can use a
thermometer to check if heat is being made or used up.
Write a heading and try the work below.
1. Look at the table below and fill it in as you do experiment
1.22.
What I added
together
what happened
chemical reaction?
2. The type of energy made in these reactions was _________.
3. Apart from the heat energy that is made, the other type of
energy made when substances burn is __________? (hint:
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think about sitting in a room with no lights on but with a fire
burning.)
Everyday chemical reactions
Read
Lots of changes take place in the world around us but it is not
always easy to decide whether these changes involve a chemical
reaction or not.
Think about freezing water. The water
changes in to ice but the ice is still
water but in the solid state. No new
substance is formed so freezing is not a
chemical reaction. Boiling water is also
not a chemical reaction because the
steam that is made is just water. No new substance has been
made.
Baking a cake, however, is a chemical
reaction because the substances we add
together like flour, butter, eggs, milk
and sugar are changed into new
substances.
Write a heading and try the work below
1. Freezing or boiling water not are not chemical reactions
because __________________________________.
2. Is Melting ice a chemical reaction? Yes/No.
3. Collect the sheet called “everyday chemical reactions?” and
complete it before you stick it into your jotter.
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The speed of chemical reactions
Read
Some reactions go faster than others. An
explosion is an extremely fast reaction,
making toast is a reaction that happens in
minutes while a car rusting or a body
rotting will take years.
Your teacher might demonstrate
some reactions for you (demo 1.24).
Try the work below.
1. Complete the table below by ticking the correct boxes.
Chemical reaction
Reaction speed
slow
medium
fast
hydrogen exploding
a car rusting
a cake baking
coal burning
crude oil forming
firing caps in a toy gun
Particle size and the speed of reactions
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Read
The speed of a reaction can be affected by using different
sizes of particles.
Your teacher will demonstrate some reactions for you (demo
1.25):

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Burning magnesium ribbon and magnesium powder.
Burning and iron nail and iron powder.
Burning normal sugar and icing sugar.
Try the work below.
1. Collect experiment card 1.26, do the experiment then
answer the questions below.
a) When I added the tablet to the acid I knew a reaction
had occurred because b _______ were formed.
b) I knew which reaction was the fastest because
___________________________.
c) Two things I did to make sure the two experiments were
fair were _________________________________
_________________________________________
d) Copy and complete the sentence below.
The __________ the particles the __________ the reaction.
2. Which will burn faster - small pieces of coal or large lumps
of coal?________________________
3. Which will burn faster - a wooden log or
sawdust? ______________________
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4. Which will cook faster - small potatoes or large potatoes?
__________________________________
5. Dr Webster was running late and
wanted her barbecue to light quickly.
She had a choice between using
charcoal lumps or broken pieces of
charcoal she found at the bottom of
an old bag of charcoal. Which would
be the best to use and why?
____________________________
______________________________________________
______________________________________________
6. It can be extremely dangerous to light a match in an icing
sugar factory but not so dangerous in a sugar lump factory
because the smaller icing sugar particles react faster/slower
than the larger sugar lumps.
Temperature and the speed of reactions
Read
The temperature of chemicals can affect how fast they will
react together.
Watch your teacher demonstrate how to do the next
experiment before you start.
measuring
cylinder
Hydrochloric
acid
beaker
The time for the reaction can be measured
timing how long
Sodium by
thiosulphate
it takes for the cross to disappear.
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Collect experiment card 1.27 and do the experiment. Then
write a heading and try the work below.
1. The aim of the experiment (what were you trying to find out)
was___________________________________________
2. I measured the time for the reaction by using a _________.
3. I changed the temperatures by _____________________.
4. Complete he table below with your results.
time for the cross to dissapear(sec)
Temperature(C)
5. In conclusion I can say the higher/lower the temperature
the faster the reaction.
6. The three things I did to make sure that the three
experiments you did were fair were
(i)
(ii)
(iii)
7. Complete the sentence below.
The ________ the temperature the __________ the reaction.
8. Food rot faster in a fridge/freezer.
9. Plants grow faster in a greenhouse /outside.
10.Explain your answer to question 9.
_______________________________________________
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11. Sarah carried out an
experiment to compare
the speed of the reaction
of a metal with some
acid. Her results are
shown in the table below.
Temperature(C) time for all of
the metal to be
used up (sec)
0
78
20
45
40
23
60
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Copy and complete the sentences below
As the temperature increases, the time for the metal to
be used up _________________.
As the temperature increases the reaction gets
____________________.
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Concentration
Read
Before we learn about how concentration can change the speed
of reactions we need to understand what the concentration of a
solution is.
The concentration of a solution tells us about how much solid
has been dissolved in water. The amount of the solid is
measured is not measured in weight but it is measured in units
called moles. Just like time is measured in units called
minutes, concentration is measured in units called moles per
litre.
If one mole of salt is dissolved in one litre of water we say it
has a concentration of 1 mole per litre.
One mole of
salt
Salt solution,
concentration =
1 mole per litre
One litre of
water
If two moles of salt is dissolved in one litre of water we say it
has a concentration of 2 moles per litre.
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The more salt dissolved in the water the greater the
concentration of the solution.
The concentration of all solutions can be measured in moles per
litre eg the acid you used in the last experiment had a
concentration of 1 mole per litre. A solution that has a
concentration of 2 moles per litre is more concentrated that a
solution that has a concentration of 1 mole per litre.
To turn a concentrated solution into a dilute one we can add
water.
Write a heading and try the following work in your jotter.
1. The concentration of a solution tell us how much _______
has been dissolved.
2. Concentration measured in m______ p___ l________.
3. Describe how you would make a salt solution that has a
concentration of 2 moles per litre. You may use a diagram if
you wish.
4. Copy and complete the sentence below.
The more salt dissolved in the water the _________________ the
concentration.
5. Which solution is the most concentrated? (circle the answer)
A
1 mole per litre
B
3 moles per litre
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6. Which solution is the most dilute? (circle the answer)
A
4 moles per litre
B
2 moles per litre
7. You would add ________ to a concentrated acid if you
wanted to dilute it.
8. When water is added to an acid the concentration of the acid
will be higher/lower.
Concentration and the speed of reactions
Read
The concentration of a solution can change the speed of a
reaction.
Collect the experiment card called PPA 2, do the experiment
and write any results as notes into your jotter. Then Write a
heading and try the work below.
1. The aim of the experiment (what were you trying to find out)
was ________________________________________
2. I knew when all of the magnesium had reacted because
___________________________.
3. The concentration of acid was changed by adding w______.
4. My conclusion (what I found out) was
______________________________________________
______________________________________________
5. Two things I did to make sure that the three experiments
you did were fair were
______________________________________________
______________________________________________
6. John did this experiment but each time he dropped the
magnesium in it floated and was not all covered by the acid.
This meant that reaction time was faster/slower because all
of the metal was not covered.
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7. Copy and complete the sentence below.
The ________ the concentration the __________ the
reaction.
Your teacher may ask you to complete a PPA assessment sheet
now.
Continue your work by trying the questions below
1. A pupil did three experiments in different concentrations of
acid –(A)1 mole per litre acid, –(B)2 moles per litre acid and–
(C) 3 moles per litre acid.
a) Reaction ___ would be fastest
2. This is due to
______________________________________________
______________________________________________
3. Look atthe diagrams below which show an experiment with an
acid and zinc metal and answer the questions on the next
page.
B
A
1 mole per litre acid
10C
zinc powder
1 mole per litre acid
10C
zinc lump
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C
1 mole per litre acid
20C
zinc powder
a) The two experiments you would set up to compare the effect
of particle size on the speed of a reaction are __ & __.
b) The two experiments you would set up to compare the effect
of temperature on the speed of a reaction are __ & __.
c) Which reaction would be faster - B or C? This is due to
_________________________________________.
Catalysts
Read
Another way to speed up a chemical reaction is to use a
chemical called a catalyst.
A catalyst speeds up a reaction but is not used up so it can be
used over and over again.
Your teacher may demonstrate (demo 1.29) a reaction where a
catalyst can be used to speed up a reaction to make oxygen.
Glowing splint
Glowing splint
Hydrogen
peroxide
Hydrogen
peroxide +
catalyst
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Try the work below
1. The name of a chemical that can be used to speed up a
chemical reaction is a ________________.
2. It possible to use a catalyst more than once because
catalysts are n__ u_____ up.
3. Draw a diagram of the demonstration that you saw and add
bubbles where you say them.
4. In the experiment without the catalyst the glowing splint
did/did not relight.
5. In the experiment with the catalyst the glowing splint
did/did not relight.
6. This tell you that the name of the gas that is made in the
reaction is o_________.
7. The reaction which made the gas the fastest was the
one with/without the catalyst.
8. Your teacher used 1g of catalyst in the second experiment.
a) How much catalyst would there be after all of the
solution had reacted? __________________
b) To separate the catalyst from the solution to use it
again you would f_________ it.
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9. Copy the sentences below.
Use of catalysts
Catalysts are often used in motor car exhaust systems.
The part of the exhaust that contains the catalyst is
called a catalytic convertor. The catalytic convertor
changes harmful and poisonous gases into safer ones
that can go out into the air.
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Enzymes
Read
An enzyme is the scientific word for a catalyst that is found in
living things. Enzymes have many important uses in industry:
Your teacher may show you a vidoe about enzymes (SS16)
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Enzymes can help make jeans look faded.
Enzymes can be used to
remove stains.
Enzymes can be used to make foods eg bread, beer, cheese
and fruit juice.
Write a heading and try the work below
1. What is the special name for a catalyst that can be found in
living things?
2. List some uses of enzymes in industry.
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You are now going to do an experiment using an enzyme called
pectinase to make apple juice.
Collect experiment card 1.30 and follow the instructions on
the sheet. Then continue with the work below.
1. The only difference between your two
experiments was
_______________________________
_______________________________
2. Two factors you had to make sure you
kept the same to keep the experiment
fair were using the same a__________
of apple sauce and same v_________ of liquid.
3. Copy the diagram from the instruction card 1.30 part 7 and
label it with the following labels:
apple sauce + pectinase
filter funnel
filter paper
measuring cylinder
apple sauce + water
clamp stand
4. Draw a line on the measuring cylinders in
your diagram to show how much juice was in
each cylinder?
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5. The process that I used to separate the juice from the solid
apples was called ________________________________.
6. The experiment which produced the most juice was
_____________________________________________.
7. We did the same experiment last year but we used apples
that had been cut up into quarters. This meant that the
speed that we collected the juice was faster/slower.
8. Factories that make fruit juice buy pectinase because
_________________________________________.
9. Read the passage below
Cellulose is the name of an enzyme that is used to make
jeans look more faded.
Yeast contains an enzyme called zymase which changes
sugars into alcohol for drinks.
Protease is the name of an enzyme that is added to
detergent powders to assist the removal of stains from
clothes.
To make meat more tender an enzyme called papain is
added.
The enzyme called pectinase is used to make fruit
juices.
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Now complete the table using the information.
Name of Enzyme
Use of Enzyme
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10. Use the information in the passage below to complete the
flow diagram.
protein
s
Key
= chemical
= enzyme
The proteins in the food we eat contain large molecules
and before we can make use of them, we must break
them down into much smaller molecules called amino
acids.
The breakdown starts in the stomach where the
enzymes, pepsin and trypsin convert the proteins into
peptides. The peptides move into the small intestine
and using enzymes called peptidases break down into
small amino acids.
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Word equations
Read
A word equation is a short way to write down what happens in a
chemical reaction. There is set of rules for writing equations.
1. Draw an arrow in the middle of a line.
2. Write the names of the chemicals we start with on the left
of the arrow separated by + signs.
3. Write the names of the chemicals that are made on the
right of the arrow separated by + signs.
Look at the example below.
When methane reacts with oxygen the new substances that are
made are water and carbon dioxide.
The word equation for this reaction will be:
Methane + oxygen
water +
carbon
dioxide
It is better to write the names of chemicals on two lines like
carbon dioxide in the example above) to make sure that the
chemicals are on the correct sides of the arrow.
The chemicals we start with are called reactants (methan and
oxygen).
The chemicals we make are called products (water and carbon
dioxide)
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Write a heading and try the work below.
1. A word equation is a short way to
___________________________________________
2. The reactants go on on the ________ of the arrow.
3. The products go on the __________ of the arrow.
4. The sentences below tell you about some chemical reactions.
Underneath each sentence write a word equation for the
reaction.
a) When calcium reacts with oxygen a new substance called
calcium oxide is made.
____________________________________________
b) When copper reacts with chlorine a new substance called
copper chloride is formed.
_____________________________________________
c) When iron reacts with fluorine a new substance called iron
fluoride is made.
_____________________________________________
d) Magnesium chloride is made when magnesium reacts with
chlorine.
_____________________________________________
e) Sodium bromide is made when sodium reacts with bromine.
______________________________________________
f) When aluminium is added to hydrochloric acid two new
substances are made. The new substance are called
aluminium chloride and hydrogen.
_______________________________________________
g) Sodium hydroxide and hydrogen are made if sodium is added
to water.
_______________________________________________
h) Petrol burns in oxygen to make carbon dioxide and water.
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i) Sugar burns in oxygen to give carbon dioxide and water.
_______________________________________________
j) If mercury oxide is heated it can be turned into mercury and
oxygen.
_______________________________________________
5. Complete the table below to show the reactants and the
products for each of the reactions you did for question 1. The
first one has been done for you.
reaction
a
reactants
calcium and oxygen
b
c
d
e
f
g
h
i
j
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products
calcium oxide