Chapter 8
Chemical Reactions
Exothermic and endothermic reactions
In a chemical reaction there is usually a
temperature change.
In an EXOTHERMIC
reaction, the
temperature goes
UP. Heat energy is
given OUT.
In an ENDOTHERMIC
reaction, the
temperature goes
DOWN. Heat energy
is taken IN.
Exothermic and endothermic reactions
Examples of EXOTHERMIC reactions:
Combustion is a common example of an exothermic reaction.
Methane + oxygen 🡪 Carbon dioxide + water + Heat
energy
Carbon + oxygen 🡪 Carbon dioxide + heat energy
(coal)
Exothermic and endothermic reactions
Examples of EXOTHERMIC reactions:
Neutralisation is another example of an exothermic
reaction.
Acid + Alkali 🡪 Salt + Water + Heat energy
Exothermic and endothermic reactions
Examples of EXOTHERMIC reactions:
Neutralisation is another example of an exothermic
reaction.
Acid + Alkali 🡪 Salt + Water + Heat energy
The symbol to show a change in the amount of
heat energy is ∆H (pronounced delta H)
Exothermic and endothermic reactions
Loss of energy
For an EXOTHERMIC
reaction, ∆H is negative.
This means that heat has
been lost from the
reaction. (release to the
surrounding)
Increasing energy
reactants
products
Time
The process of burning (Combustion)
During the process of burning (wood or coal), the
chemical energy is converted into:
-
Light energy
Thermal energy
Sound energy
These energies are dissipate to the surrounding.
Burning hydrogen and oxygen to form water
The atoms of hydrogen and oxygen rearrange themselves to give out energy.
Chemical energy is changed into
- Kinetic energy
- Thermal energy
- Sound energy
- Light energy
Reaction of magnesium and oxygen
Chemical energy is changed into
- Thermal energy
- Light energy
Reaction of magnesium and oxygen
Chemical energy is changed into
- Thermal energy
- Light energy
Any substance that combines with oxygen is an
OXIDATION REACTION
More examples of exothermic reactions
-
Reaction of potassium with water
The energy stored is changed to thermal energy
-
Reaction of magnesium with hydrochloric acid
The energy stored is converted to thermal energy
TB Page 264
1. Oxygen, fuel and energy to start off the reaction
2. An exothermic reaction is a reaction that releases
(dissipates) thermal energy to the surrounding.
3. Burning releases heat, light, and sound energy.
TB Page 267 Qs 4 - 8
4. Magnesium chloride and hydrogen
Magnesium + hydrochloric acid -> magnesium chloride + hydrogen (gas)
Reactants
Products
5. When is not fizzing (bubbling) anymore, the reaction has completed.
When the temperature dropped after it raised, it can indicates that the
reaction has completed.
6. Sofia is correct because the differences between the start and the end
temperatures are the same, which is 24 degree.
TB Page 267 Qs 4 - 8
7. Safety glasses (safety goggles) help to prevent the case of acid
spills or spits into the eyes.
8. Does adding more magnesium to the hydrochloric acid increase
the temperature in the reaction?
Does adding a different metal to hydrochloric acid result in increase
in the temperature in the reaction?
Does changing the acid used in the reaction increase the
temperature change?
WB page 159 - 165
8.1 A
1. Independent (manipulate - changing) - the length of
magnesium ribbon
2. Dependent variable (Responding variable - results) temperature change of acid
3. Concentration of hydrochloric acid, initial temperature of
acid, volume of hydrochloric acid
4. 17.0; 17.0 ; 17.5 (make sure the decimal pt is consistent)
WB page 159 - 165
Exercise 8.1 A
5. The results show the increase in the length of the ribbon
increase the end temperature but it makes very little
difference to the end temperature
6. No. Because they only have 3 length of magnesium ribbon
and it is in a very small range.
7. 0.5 cm
Describe - bring in the results
WB page 159 - 165
Exercise 8.1 A
8. Larger interval should be used. This is because larger interval
will make the temperature changes more obvious (clear)
9. >5
10. Wrap the test tube with some cotton or cloth to prevent heat
loss but still being able to read the thermometer.
11. Repeat the experiment for at least 3 times and calculate the
average
WB Page 161
Exercise 8.1 B
1.
1.
Magnesium + sulfuric acid -> magnesium sulfate + hydrogen gas
Hydrochloric acid - metal chloride
Phosphoric acid - metal phosphate
(a) The type of metal
(b) amount of hydrochloric acid, type of acids
(c) the size of metal
WB Page 161
(d) There is no conclusion with these results. This is because the size of
metal used are not the same.
(e) Balance the size of metal X and metal Y. Then repeating the
experiment several times to calculate the average which will be more
accurate.
WB Page 164
Exercise 8.1 C
1. Potassium + water -> Potassium hydroxide + hydrogen
2. The chemical energy changed to thermal, light and sound energy.
3. Wear safety goggles and gloves. Carry out this experiment behind a
safety screen.
4. Measure the increase in temperature of water. However, it is very
difficult to measure the energy given as light and sound energy.
5. Method (can also list down independent, dependent and
controlled variables)
1. Prepare same amount of 4 different types metals
2. Prepare same volume of dilute hydrochloric acid in separate
test tubes.
3. Measure the initial temperature of acid in the test tube.Be sure
that the bulb of the thermometer does not touch the base of the
test tubes.
4. Drop the 4 types of metals into each test tubes. Be sure of
wearing safety goggles and gloves to prevent spill on skin.
5. Measure the temperature again after the reaction has finished
6. Calculate the change in temperature to identify which metals
produce the most increase in temperature during the reaction
6. Bar chart / bar graph
This is because it will be easier to compare the rise in
temperature for the 4 metals.
Endothermic Reactions
An endothermic reaction absorbs heat from its environment.
The absorbed energy provides the activation energy for the reaction to occur.
A hallmark of this type of reaction is that it feels cold.
Exothermic and endothermic reactions
Examples of ENDOTHERMIC reactions:
Endothermic reactions tend to be less common.
Dissolving ammonium nitrate crystals in water is an
endothermic reaction.
Ammonium + Water 🡪 ammonium nitrate – Heat
nitrate
solution
energy
Temperature of reactants = 20oC
Temperature of products = 13oC
The sherbet sweets
-
Mixture of dry citric acid and sodium
hydrogencarbonate
When the citric acid and sodium
bicarbonate touch your saliva, they
react together to make bubbles that fizz
and pop in your mouth. The icing sugar
gives it a nice taste.
Examples of endothermic reactions
1. Reaction of potassium chloride and water
- Potassium chloride absorbs heat from its surroundings when it dissolves in
water.
- The beakers feels cold
Examples of endothermic reactions
2. Melting
-
As the thermal energy is absorbed from the surroundings, the particles have
enough energy to overcome the forces of attraction.
Exothermic and endothermic reactions
Let’s just
recap
Exothermic and endothermic reactions
Let’s just
recap
EXOTHERMIC
Exothermic and endothermic reactions
Let’s just
recap
EXOTHERMIC
Heat is given out
Exothermic and endothermic reactions
Let’s just
recap
ENDOTHERMIC
Exothermic and endothermic reactions
Let’s just
recap
ENDOTHERMIC
Heat is taken in
Using exothermic reaction
How does it work?
In self heating foods:
-
The compartment is in two parts, separated by foil. The packaging is
designed such that the hot water sits below the tray of food and steams it.
Heat is generated by an exothermic reaction caused by adding roomtemperature water to powdered minerals such as magnesium, iron and salt.
The heating agent and responsible reaction vary from product to product
Calcium oxide is used in the following reaction:
CaO(s)+ H2O(l) → Ca(OH)2(s) Calcium oxide + Water -> Calcium hydroxide
Copper sulphate and powdered zinc can also be used, but this process is less efficient:
CuSO4(s) + Zn(s) → ZnSO4(s) + Cu(s)
TB page 271
1. (a) Reactants - sodium hydrogencarbonate & citric acid
(b) Products - sodium citric, water, carbon dioxide
2. A reaction that absorbs / take in heat from the environment.
3. This is because an endothermic reaction has occurred. In
the sherbet sweets is a mixture of dry citric acid and sodium
hydrogencarbonate . As these chemicals react with saliva,
heat from the mouth will be taken in and hence our mouth will
feel cooler.
4. This is because carbon dioxide is being produced.
TB page 272
5. It is a process because no new products are being formed.
So, it is a changed of state, not a chemical reaction.
6. Evaporation, changes from liquid to gas
7. During the process of swimming, heat energy from our skin is
taken by water particles and evaporate into gas. This is an
endothermic process as you feel colder.
8. Water freezing is an exothermic process. This is because the
heat has to be lost to the surroundings so that the particles will
lost energy, can only vibrate instead of move past one another.
TB pg 275
9. This is because the can and chemicals can only be used once. They have to be
made so that the chemicals used to warm the food or drink do not come into
contact with it.
10. This is because the chemicals inside self heating container is irreversible.
They cannot produce anymore heat.
11. Freezer ice pack - Adv - reusable and can be used many times.
Disadv - must have access to fridge
Chemical ice pack - Adv - no need to access to fridge or freezer
Disadv - expensive and non-
reusable
WB page 166
Exercise 8.2 A
1. Reaction A - Exothermic
Reaction B - Exothermic
Reaction C - Endothermic
Reaction D - Exothermic
1. Endothermic Reaction
2. Exothermic Reaction
WB page 167
Exercise 8.2B
1. (a) Endothermic reaction - sodium hydrogen carbonate & citric acid
Exothermic reaction - sodium hydroxide and sulfuric acid; hydrochloric acid
and zinc; copper sulfate and magnesium powder.
(b) Copper sulfate and magnesium powder
(c) This is because polystyrene is a good insulator of heat so less of heat
energy produced in the reaction was lost to the environment. Hence, the
results is more accurate
WB page 167
Exercise 8.2B
2. Heat bag; self heating bottle; self heating food container
3. Chemical ice-packs
WB page 167
Exercise 8.2C
1. Endothermic reaction involves the formation of new products. An
example of endothermic reaction is the reaction of sodium hydrogen
carbonate with citric acid. This will produce sodium citrate, water and
carbon dioxide.
In an endothermic process, energy is absorbed but no new products are
being formed. For example, the melting of ice is an endothermic process
since no new products are formed.
WB page 167
Exercise 8.2C
2. The water in the bowl soaks into cloth over the soda bottles. The liquid
evaporates as it heats up in the hot weather. The particles in the liquid move
all the time and can slide past each other as they only have weak force
holding them in place. The more energy the particles have, the more they can
move. When the particles have enough energy transferred from the
surroundings, they will escape and change into gas to evaporate. Since the
energy to do this comes from the surrounding water in the bowl, the water
cools down and keeps the bottles of soda cool.
8.3 Reactions of metals with oxygen
Properties of metals:
1.
2.
3.
4.
5.
6.
7.
Shiny metallic
Ductile
Malleable
High melting and boiling points.
High density
Good conductors of electricity and heat
Reaction with oxygen and water will result in corrosion and rust
magnesium + oxygen ->
magnesium oxide
The magnesium gains mass
(gets heavier) because oxygen
adds its mass to the
magnesium
Total final mass of the product = mass of magnesium + mass of
oxygen
Magnesium oxide (after heating) = Total final mass – mass of the
crucible
Oxygen = Total final mass – mass of crucible – mass of magnesium
BUT wait a minute – How can
adding oxygen make something gain
mass. Does oxygen have any mass?
Oxygen is in the air – can you
weigh air?
Total mass of substances at the beginning and the
end of burning must be the same
Magnesium + oxygen -> magnesium oxide
(Reactants)
(Products)
Total mass
is the same
From this came - LAW OF CONSERVATION OF MASS
During a chemical reaction the total
masses before and after stay the same
LAW OF CONSERVATION OF MASS
Magnesium + oxygen = magnesium oxide
Since the magnesium joins to the oxygen in the
air, then if you add together the mass of the
piece of magnesium and the mass of oxygen it
joins to, then it must be equal to the mass of the
magnesium oxide formed.
More examples equations
magnesium + oxygen → magnesium oxide
reactants
product(s)
magnesium + hydrochloric acid → magnesium chloride + hydrogen
reactants
products
The signs of a chemical reaction
●fire - huge flames/tiny sparks
●smell - sweet smell/stink
●temperature change - gets hotter/cooler
●sound - loud bang/gentle fizzing
●end product - different from the reactants
The reaction between iron and oxygen
When iron is left in damp air, it will rusts and corrode
Iron + oxygen -> iron oxide
What is corrosion?
- Gradual damage caused to metal, stone, or other materials by corrosion.
- When iron is exposed to the air, a bright orange compound called rust forms on the
surface . It breaks down iron objects
Rusting is an oxidation process
●The iron reacts with water and oxygen to form hydrated iron(III) oxide,
which we see as rust.
●Iron and steel rust when they come into contact with WATER and
OXYGEN
Anhydrous Calcium
Chloride
used as a drying agent
The Effects of Corrosion
• Damage to commercial airplanes or vehicle electronics
• Damage to hard disks and computers used to control complicated
processes (e.g. power plants, petrochemical facilities or pulp and paper
mills).
• Damage to server rooms and data centres.
• Damage to museum artefacts
• Costs of repairing or replacing household equipment that fails
How can iron be protected?
There are several ways to prevent iron
from rusting.
● oiling – for example, bicycle chains
● greasing – for example, nut and bolts
● painting – for example, car body
panels
● coating with a thin layer of plastic
Galvanising
● The iron or steel object is coated in a thin layer of ZINC.
● This stops oxygen and water reaching the metal underneath – but the zinc
also acts as a sacrificial metal.
● Zinc is more reactive than iron, so it oxidises rather than the iron object.
Sacrificial protection
● A reactivity series lists metals in order of how reactive they are.
● Magnesium
and zinc are often used
as sacrificial metals. They are more reactive
than iron and lose their electrons in preference
to iron. This prevents iron from losing its
electrons and becoming oxidised.
Homework
TB page Pg 279 - Qs 1 - 3
Pg 280 - Qs 4 - 8
WB page 169 - 171
TB page 279
1. It is soft enough to be easily cut by knife.
2. The metal can be reactive and may react with moisture on the
skin.
3. Sodium + oxygen -> sodium oxide
4. Dry air (it should not be in the presence of air and water)
5. Test tube 2. It contains water and air
6. This is to make sure that it is a fair test following the usage of
same types of nail.
7. It contains calcium chloride which absorb moisture from the
air.
TB page 279
8. The layer of oil on the surface kept away the air from the nailed.
Besides, boiled water also removed any air dissolved in it.
WB page 170
1. Iron oxide
2. Test tube B
3. The layer of oil prevent the air from in contact with the nail.
Besides, boiled water also removed any air dissolved in it.
4. (a) No
(b) This could be due to Zara failed to put the stopper firm
enough and some moist air could have entered.
1. Painting, greasing, oiling or galvanising
WB page 171
Controlled variable - types of nail, the volume of water and the time for
experiment
Independent variable - temperature of water (Heat pack or ice pack)
dependent variable - the amount of rust produce.
Procedure:
1. Firstly, select two similar types of iron nail and measure 50 cm3 of water
with measuring cylinder.
WB page 171
2. Heat up one of the water to 80 degree celsius and let the other
be at room temperature. Then, measure the initial weight of the
iron nails.
3. Drop the iron nails into each test tube and cover each tubes with
cork. Leave the test tubes for 2 days.
4. After 2 days, take out the iron nail from each test tubes and
compare how much rust has been produced. This can be done by
eye or measure the increase in weight.
5. Tabulate the results and draw a conclusion to show at which
temperature, the iron nail will rust more quickly.
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
INCREASING
REACTIVITY
The Reactivity Series
Very
reactive
Quite
reactive
Not so
reactive
Unreactive
{
{
{
{
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
INCREASING
REACTIVITY
The Reactivity Series
Reaction with water
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Very vigorous reaction with water, forming the
hydroxide. Fizzes, and hydrogen is released.
General Equation:
Metal + water -> metal hydroxide (Alkali) + hydrogen
Going down the series, the metals become more reactive,
and react more vigorously with water. They float, may
melt and the hydrogen gas produced may ignite
Lithium reacts gently, sodium more violently, and
potassium so violently that it melts and bursts into
flames.
Reaction with water
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Slow reaction with cold water (very slow
in the case of magnesium) to form the
hydroxide. Bubbles of hydrogen gas will
be seen.
General Equation:
Metal + water -> metal hydroxide + hydrogen
Reaction with water
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Do not react with cold water, but will
react with steam to form the oxide.
Hydrogen gas is produced.
Al(s) + 3H2O(l) 🡪 Al2O3(s) + 3H2(g)
General Equation:
Metal + water -> metal oxide + hydrogen
Reaction with water
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
No reaction with water or
steam.
They are chemically INERT
Tests for gases
You need
to know
these!
Tests for gases
1. Hydrogen
Hydrogen gas
Hydrochloric acid
Magnesium ribbon
Tests for gases
1. Hydrogen
Hydrogen gas
Hydrochloric acid
Magnesium ribbon
Tests for gases
1. Hydrogen
POP!
Hydrogen gas
Hydrochloric acid
Magnesium ribbon
Tests for gases
1. Hydrogen
To test for
hydrogen, use a
burning splint.
The gas will
explode with a
squeaky ‘pop’.
POP!
Hydrogen gas
Hydrochloric acid
Magnesium ribbon
Tests for gases
2. Oxygen
Oxygen gas
Hydrogen peroxide
Manganese (IV) oxide
Tests for gases
2. Oxygen
Glowing splint
Oxygen gas
Hydrogen peroxide
Manganese (IV) oxide
Tests for gases
2. Oxygen
Splint re-lights
Oxygen gas
Hydrogen peroxide
Manganese (IV) oxide
Tests for gases
2. Oxygen
To test for oxygen,
use a glowing splint.
The gas will cause the
splint to re-light.
Oxygen gas
Hydrogen peroxide
Manganese (IV) oxide
Splint re-lights
Tests for gases
3. Carbon dioxide
Delivery tube
Bubbles of carbon
dioxide
Hydrochloric acid
Calcium carbonate
Limewater
Tests for gases
3. Carbon dioxide
Delivery tube
Bubbles of carbon
dioxide
Hydrochloric acid
Calcium carbonate
Limewater
Tests for gases
3. Carbon dioxide
To test for carbon dioxide,
bubble the gas through
limewater. After a short
while the limewater will go
milky-white.
Bubbles of carbon
dioxide
Hydrochloric acid
Calcium carbonate
Delivery tube
Limewater
Tests for gases
3. Carbon dioxide
To test for carbon
dioxide, bubble the gas
through limewater. After
a short while the
limewater will go milkywhite.
Bubbles of carbon
dioxide
Hydrochloric acid
Calcium carbonate
Delivery tube
If carbon dioxide
continues to be
bubbled through
limewater, the liquid
will eventually go
clear again.
Limewater
TB Page 284
1. Sodium + water -> sodium hydroxide + hydrogen gas
2. Safety goggles and gloves need to be worn. Use only
small pieces of metals and the metals should be moved
using tongs
3. The metals should be stored under oil to prevent the
reaction with the moisture in the air that may cause
explosion.
TB Page 284
4. Hydrogen gas is given off. You could test this gas by using
lighted splint or candle. If the gas is hydrogen, a squeaky
pop sound will be produced.
5. We can compare the reactivity by measuring the volume of
hydrogen gas produced.
● If the metal is more reactive, more hydrogen gas will be
produced
TB Page 284
6. Same mass of calcium and magnesium; same volume of
liquid; similar initial temperature of water; the amount of time
set for the metals to react.
7. Calcium + water -> calcium hydroxide + hydrogen gas
9. Platinum, gold, silver
10. They are chemically inactive / unreactive
TB Page 284
6. Same mass of calcium and magnesium; same volume of
liquid; similar initial temperature of water; the amount of time
set for the metals to react.
7. Calcium + water -> calcium hydroxide + hydrogen gas
9. Platinum, gold, silver
10. They are chemically inactive / unreactive
Reaction of metals with dilute acids
Before we start, write down as many of the words equations as you can.
You have 1 minute to do so.
Oxygen + sodium ->
Oxygen + magnesium ->
Oxygen + iron ->
Water + potassium ->
Water + calcium ->
Magnesium + steam -> magnesium oxide + hydrogen
General equations of metal reacting with acid
Metal + acid -> salt + hydrogen
Example:
Magnesium + hydrochloric acid -> magnesium chloride + hydrogen
Magnesium + sulphuric acid -> magnesium sulphate + hydrogen
Observation (Please write what you see ONLY)
When a metal is put in acid,
- It gets smaller and smaller as it
gets used up in the reaction .
- Bubbles of gas can be seen.
(Never answer bubbles of
hydrogen gas can be seen.
You cannot see hydrogen
gas)
Hydrogen gas can be proven
using a burning splint*
Salt formation
Acid
Salts formed
Hydrochloric acid
chlorides
Sulphuric acid
sulphates
Nitric acid
nitrates
Phosphoric acid
phosphates
Reactions of salts
Acids + Metals
Acid + Metal 🡪 Salt + Hydrogen
Reactions of salts
Acids + Metals
Acid + Metal 🡪 Salt + Hydrogen
Magnesium + Hydrochloric 🡪 Magnesium + Hydrogen
Acid
chloride
Reactions of salts
Acids + Metals
Have you got that?
Are you really sure?
Let’s try a few
examples.
Reactions of salts
Acids + Metals
Magnesium + Sulphuric Acid 🡪
Iron + Hydrochloric Acid
🡪
Lead
🡪
+ Sulphuric Acid
Reactions of salts
Acids + Metals
Magnesium + Sulphuric Acid 🡪 Magnesium sulphate +
Hydrogen
Iron + Hydrochloric Acid
Lead
+
🡪 Iron chloride + Hydrogen
Sulphuric Acid 🡪 Lead sulphate + Hydrogen
An Investigation into the reaction of metals in acid
Refer to the task in google classroom
Homework
TB page 287 Question 1-4
Page 291 - 292 all questions
WB page 171 - 183
TB page 287
1. Magnesium + sulfuric acid -> magnesium sulfate +
hydrogen
1. Magnesium sulfate
2. Bubbles of gases can be observed. The temperature
will also increase. The magnesium ribbon will disappear
3. Zinc + nitric acid ->zinc nitrate + hydrogen
Check your progress
8.1
a. Burning / magnesium ribbon placed in hydrochloric acid
(HCl)
b. Sodium hydrogencarbonate added to citric acid
c. Decreases
d. Melting ice / evaporation
e. Exothermic
8.2
(a)The type of fuels
(b)Amount of fuel and amount of water / The time he heats
it for
(c)He must measure the initial and final temperature of the
water for each of the fuels. The fuels that produces
largest rise in temperature gives out the most energy.
(d)Wear gloves, use tongs to hold the hot beaker, wear
safety glasses
8.3
(a)Carbon + oxygen -> carbon dioxide
(b)Sodium hydroxide + hydrochloric acid -> sodium
chloride + hydrogen
(c)Magnesium + oxygen -> magnesium oxide
(d)Potassium + water -> potassium hydroxide + hydrogen
8.4
(a)The more calcium you add, the greater the increase in
temperature.
(b)The temperature increases about 5 degree Celcius
(c)Zara’s results - 1, 2, 3, 4
Arun’s results - 1, 1, 3, 4
(d)
Mass of calcium added in g
Mean temperature change in degree
celsius
1
1.0
2
1.5
3
3.0
4
4.0
(e) (i) Mass in Calcium (g)
(ii) Temperature change (degree Celsius)
(f) No. This is because they have increase the volume of
water which may change the temperature of water.
WB Pg 172
Exercise 8.4
1.
2.
3.
4.
Potassium -> magnesium -> zinc -> copper
Potassium + water -> potassium hydroxide + hydrogen
Sodium or lithium
Copper can be used because it does not react with water,
magnesium despite react slowly, it will still react when there is
rain or snow.
5. Calcium + water -> calcium hydroxide + hydrogen
7. Hydrogen
8. Place a lighted splint in the gas to see whether it
makes a pop sound during burning
9. Magnesium + steam -> magnesium oxide + hydrogen
11. Copper is used because it does not react with water. Iron will
react with oxygen in the presence of water to form iron oxide .
This will result the water being coloured reddish brown and the
pipe will collapse due to rust
Exercise 8.5 A
1. Test tube C because the volume of hydrochloric acid is not
the same as in the rest of the test tubes. This will make the
result not reliable (The volume of acid - control variables)
2. They have put on safety glasses / goggles.
3. This is because metal A is using nitric acid whereas metal B,
C and D are using hydrochloric acid. (The type of acid - control
variable)
4. No. This is because metal B appeared to be larger than other
pieces of metal. (The size of metal - control variable)
5. The type of metal that are most reactive with dilute acids
6. The type of metal
7. The amount of bubbling/ number of bubbles there are when
reacting with metal
8. The volume of acid, the type of acid, the mass of metal, same
initial temperature.
Exercise 8.5B
1. bubbles are given off/ change in temperature / Reaction
has occur if there is a colour change/ .
2. Compare the amount of bubbles produced/ calculate the
temperature change
● Colour change does not show reactivity.
1. This is because the boys have used different acids with
different concentrations and volume
Concentration and temperature affect rate of reaction
Temperature
1. Providing more energy -> increase k.e (movement)
2. Produce more collision -> higher rate of reaction
Concentration
1. Higher concentration -> number of particles
present per unit volume is higher
2. More collision -> higher rate of reaction
Variables:
Control variables: The volume of acid, the concentration of acid,
the type of acid and the mass of metal.
Independent variables: The type of metal
Dependent variables: The number of bubble produced.
Procedures:
1. Measure 10 cm3 of acid using measuring cylinder for each
test tubes.
Procedures:
1. Measure 10 cm3 of acid using measuring cylinder for each
test tubes.
2. Prepare 3g of zinc, lead, copper and aluminium.
3. Drop the metal into the test tubes containing the acid.
Remember to wear safety goggles and gloves to avoid spill.
4. Observe and count the amount of bubbles produced in each
test tube.
Exercise 8.5 C
1. The mass of metal used; the volume of acid; the type of acid
and its concentration
2. Copper does not react with dilute acid
4. Mass of the metal could be different; she might have misread
the timer, she might have mixed up the metal she was using
5. Keeping the delivery tube in place so that no hydrogen is lost;
getting the delivery tube back in the conical flask after adding
the metal; being exactly sure when the tube is completely full of
gas
6. Using a graduated tube or measuring cylinders or mark the
test tube so that it is easier to see when the gas has reached
the level.
Repeating the experiment and take the average result ->
increase reliability