IGCSE CHEMISTRY FOR PRACTICE EXAM SOLUTION WITH COMPLETE QUESTIONS AND
ANSWERS
Explain what is an addition polymer - An addition polymer is large molecule made by adding many
small molecules (each containing a double bond) to form one much larger molecule
Explain what is a monomer - Monomers are the many small molecules (such as ethene) which add
together to make a polymer
Describe, in terms of structure and bonding, what happens when ethene molecules are converted
into poly(ethene) - One bond in the double bond breaks. Monomers join together to form a long
chain. Polymer contains only single bonds
Draw the equation to show the formation of poly(ethene) -
Draw the equation to show the formation of poly(propene) -
Draw the displayed formula for the repeat unit of poly(ethene) -
Draw the displayed formula for the repeat unit of poly(propene) -
State the uses of poly(ethene) - Plastic bags and bottles
State the uses of poly(propene) - Plastic crates and ropes
State uses for poly(chloroethene). (Triple science only!) - Plastic piping and cable insulation
What is meant by the term biodegradable? - The break down of a substance by microorganisms
Explain why addition polymers are hard to dispose of - They are inert as they have strong C-C bonds.
This makes them non-biodegradeable.
,What type of reaction is used to form nylon? (Triple science only!) - Condensation polymerisation
During condensation polymerisation, what else forms other than the polymer? (Triple science only!) -
A small molecule such as H₂0 or HCl
What is crude oil? - A mixture of hydrocarbons
Explain how crude oil is separated into fractions - Crude oil is separated by fractional distillation.
Crude oil is heated and the oil evaporates.
It then goes into the tower.
As the vapours rise up the tower the temperature falls.
Different sized fractions condense at different heights because they have different boiling points.
Smaller molecules condense high up the tower.
Larger molecules condense low down in the tower.
Then the fractions are collected.
Recall the names of the main fractions obtained from crude oil - refinery gases
gasoline
kerosene
diesel
fuel oil
bitumen
Recall a use of refinery gases - Bottled gas
Recall a use of gasoline - Fuel for cars
Recall a use of kerosene - Fuel for aeroplanes
,Recall a use of diesel - Fuel for lorries
Recall a use of fuel oil - Fuel for ships
Recall a use of bitumen - Surfacing roads
Describe the trend in boiling points of the main fractions in crude oil - Boiling point increases as the
number of carbon atoms (chain length) increase
Describe the trend in viscosity of the main fractions in crude - Viscosity increases as the number of
carbon atoms (chain length) increase
Which fraction of crude oil has the lowest boiling point? - Refinery gases
What is meant by the term viscosity? - The viscosity of a fluid describes how easily it flows.
Water has a low viscosity, it flows very easily.
Crude oil has a higher viscosity than water, it does not flow very easily.
Which fraction of crude oil is the most viscous? - Bitumen
Explain why carbon monoxide is dangerous to humans - It is poisonous because it reduces the
capacity of the blood to carry oxygen
In car engines, sparks cause the formation of some gases which contribute to acid rain.
What are these gases? - Oxides of nitrogen
Why can nitrogen react with oxygen in a car engine? - The temperature is very high
, Describe how nitrogen oxides and sulfur dioxide contribute to acid rain - Nitrogen oxides created in
hot car engines and sulfur dioxide released when fossil fuels are burned combine with water in the
atmosphere to form acidic solutions
Write the chemical equation for sulfur dioxide dissolving in water to form acid rain - SO₂ + H₂O →
H₂SO₃
Describe the problems caused by acid rain - Acid rain damages plant life and life in lakes.
It also corrodes limestone and some metals.
Explain why cracking is an important process in the oil industry - Cracking converts long chain
hydrocarbons into short chain hydrocarbons.
Crude oil contains a surplus long chains.
Shorter chain hydrocarbons are in greater demand, e.g. petrol.
Cracking also produces alkenes which are used in making polymers and ethanol.
What is cracking? - The breaking down of long-chain alkanes into alkenes and shorter-chain alkanes
State the conditions for the cracking of hydrocarbons - Aluminium oxide catalyst heated to 600°C
Write a chemical equation for the cracking of decane - C₁₀H₂₂ → C₂H₄ + C₈H₁₈
Name the process used to extract aluminium - electrolysis
Why is aluminium not extracted in the blast furnace? - aluminium is more reactive than carbon
During the electrolysis of aluminium oxide, describe how the operating temperature is kept low -
aluminium oxide is dissolved in cryolite which melts at a lower temperature
Why is cryolite used in the electrolysis of aluminium oxide? - cryolite is used as a solvent to decrease
the operating temperature
ANSWERS
Explain what is an addition polymer - An addition polymer is large molecule made by adding many
small molecules (each containing a double bond) to form one much larger molecule
Explain what is a monomer - Monomers are the many small molecules (such as ethene) which add
together to make a polymer
Describe, in terms of structure and bonding, what happens when ethene molecules are converted
into poly(ethene) - One bond in the double bond breaks. Monomers join together to form a long
chain. Polymer contains only single bonds
Draw the equation to show the formation of poly(ethene) -
Draw the equation to show the formation of poly(propene) -
Draw the displayed formula for the repeat unit of poly(ethene) -
Draw the displayed formula for the repeat unit of poly(propene) -
State the uses of poly(ethene) - Plastic bags and bottles
State the uses of poly(propene) - Plastic crates and ropes
State uses for poly(chloroethene). (Triple science only!) - Plastic piping and cable insulation
What is meant by the term biodegradable? - The break down of a substance by microorganisms
Explain why addition polymers are hard to dispose of - They are inert as they have strong C-C bonds.
This makes them non-biodegradeable.
,What type of reaction is used to form nylon? (Triple science only!) - Condensation polymerisation
During condensation polymerisation, what else forms other than the polymer? (Triple science only!) -
A small molecule such as H₂0 or HCl
What is crude oil? - A mixture of hydrocarbons
Explain how crude oil is separated into fractions - Crude oil is separated by fractional distillation.
Crude oil is heated and the oil evaporates.
It then goes into the tower.
As the vapours rise up the tower the temperature falls.
Different sized fractions condense at different heights because they have different boiling points.
Smaller molecules condense high up the tower.
Larger molecules condense low down in the tower.
Then the fractions are collected.
Recall the names of the main fractions obtained from crude oil - refinery gases
gasoline
kerosene
diesel
fuel oil
bitumen
Recall a use of refinery gases - Bottled gas
Recall a use of gasoline - Fuel for cars
Recall a use of kerosene - Fuel for aeroplanes
,Recall a use of diesel - Fuel for lorries
Recall a use of fuel oil - Fuel for ships
Recall a use of bitumen - Surfacing roads
Describe the trend in boiling points of the main fractions in crude oil - Boiling point increases as the
number of carbon atoms (chain length) increase
Describe the trend in viscosity of the main fractions in crude - Viscosity increases as the number of
carbon atoms (chain length) increase
Which fraction of crude oil has the lowest boiling point? - Refinery gases
What is meant by the term viscosity? - The viscosity of a fluid describes how easily it flows.
Water has a low viscosity, it flows very easily.
Crude oil has a higher viscosity than water, it does not flow very easily.
Which fraction of crude oil is the most viscous? - Bitumen
Explain why carbon monoxide is dangerous to humans - It is poisonous because it reduces the
capacity of the blood to carry oxygen
In car engines, sparks cause the formation of some gases which contribute to acid rain.
What are these gases? - Oxides of nitrogen
Why can nitrogen react with oxygen in a car engine? - The temperature is very high
, Describe how nitrogen oxides and sulfur dioxide contribute to acid rain - Nitrogen oxides created in
hot car engines and sulfur dioxide released when fossil fuels are burned combine with water in the
atmosphere to form acidic solutions
Write the chemical equation for sulfur dioxide dissolving in water to form acid rain - SO₂ + H₂O →
H₂SO₃
Describe the problems caused by acid rain - Acid rain damages plant life and life in lakes.
It also corrodes limestone and some metals.
Explain why cracking is an important process in the oil industry - Cracking converts long chain
hydrocarbons into short chain hydrocarbons.
Crude oil contains a surplus long chains.
Shorter chain hydrocarbons are in greater demand, e.g. petrol.
Cracking also produces alkenes which are used in making polymers and ethanol.
What is cracking? - The breaking down of long-chain alkanes into alkenes and shorter-chain alkanes
State the conditions for the cracking of hydrocarbons - Aluminium oxide catalyst heated to 600°C
Write a chemical equation for the cracking of decane - C₁₀H₂₂ → C₂H₄ + C₈H₁₈
Name the process used to extract aluminium - electrolysis
Why is aluminium not extracted in the blast furnace? - aluminium is more reactive than carbon
During the electrolysis of aluminium oxide, describe how the operating temperature is kept low -
aluminium oxide is dissolved in cryolite which melts at a lower temperature
Why is cryolite used in the electrolysis of aluminium oxide? - cryolite is used as a solvent to decrease
the operating temperature
