IGCSE Chemistry Exam And Correct
Answer Update 2025
State the method used to obtain sand from a mixture of sand and water - Answer -
✔✔filtration
State the method used to obtain solid copper sulfate from aqueous copper sulfate -
Answer -✔✔crystallisation
State the method used to obtain red food dye from a mixture of food dyes - Answer -
✔✔paper chromatography
State the method used to obtain water from salt water - Answer -✔✔simple distillation
Draw a diagram to show equipment used in simple distillation - Answer -✔✔For what
process is this equipment used?
State the method used to obtain kerosene from a crude oil. - Answer -✔✔fractional
distillation
Draw the equipment used in fractional distillation in the lab - Answer -✔✔For what
process is this equipment used?
Explain how fractional distillation is used to separate a mixture of different liquids -
Answer -✔✔The different liquids have different boiling points
State the method used to extract the red dye from a sample of rose petals - Answer -
✔✔dissolving
Describe how pure salt can be obtained from rock salt - Answer -✔✔1) Grind rock salt
into a fine powder. 2) Add powder to hot water and stir to dissolve salt. 3) Filter mixture.
Salt solution passes through the filter paper leaving behind the sand. 4) Boil filtrate to
evaporate some of the water. 5) Leave saturated solution to cool so that crystals of salt
form. 6) Filter cold mixture to separate the crystals from the remaining solution.
Ethanol is a flammable liquid. Suggest how it could be heated safely - Answer -✔✔Use
a water bath
Explain how a chromatogram shows that different dyes are different from each other -
Answer -✔✔Each dyes has a different mixture
,State the expression for calculating molar concentration - Answer -✔✔Molar
concentration = Amount (in moles)/volume (in dm^³)
Which cation gives a crimson red flame colour? - Answer -✔✔Li⁺
Which cation gives a orange flame colour? - Answer -✔✔Na⁺
Which cation gives a lilac flame colour? - Answer -✔✔K⁺
Which cation gives a brick red flame colour? - Answer -✔✔Ca²⁺
Describe how you would carry out a flame test - Answer -✔✔Put solid onto a wire. Put
into a blue flame
How would you test for the ammonium ion? - Answer -✔✔Add sodium hydroxide. If
ammonium ions were present, ammonia gas will form which will turn damp red litmus
paper blue
Describe how you would test for Cu²⁺ ions - Answer -✔✔Add sodium hydroxide and a
blue precipitate will form
Give the formula of the blue precipitate formed when sodium hydroxide is added to a
solution containing Cu²⁺ - Answer -✔✔Cu(OH)₂
Describe how you would test for Fe²⁺ ions - Answer -✔✔Add sodium hydroxide and a
green precipitate will form
Write a word equation for the reaction between sodium hydroxide and iron(II) sulfate -
Answer -✔✔sodium hydroxide + iron(II) sulfate -> iron (II) hydroxide + sodium sulfate
Describe how you would test for Fe³⁺ ions - Answer -✔✔Add sodium hydroxide and a
brown precipitate will form
What 2 things are added to a solution to test for chloride ions? What is observed if they
are present? - Answer -✔✔Add dilute nitric acid and silver nitrate. A white precipitate of
silver chloride is formed.
Describe the test for bromide ions. - Answer -✔✔Add dilute nitric acid and silver nitrate.
A cream precipitate of silver bromide is formed.
After adding nitric acid and silver nitrate to a solution containing iodide ions, what colour
precipitate is formed? - Answer -✔✔A yellow precipitate (of silver iodide) is formed.
,Why is hydrochloric acid added before barium chloride solution in testing for sulfate
ions? - Answer -✔✔To remove carbonate ions
Describe how you would test for sulfate ions - Answer -✔✔Add dilute HCl, followed by
BaCl₂. A white precipitate will form
Write an chemical equation for the reaction between barium chloride and lithium sulfate
(Li₂SO₄). Include state symbols. Also, what would you see? - Answer -✔✔BaCl₂ (aq) +
Li₂SO₄ (aq) -> BaSO₄ (s)+ 2LiCl (aq). Observe a white precipitate of barium sulfate.
Describe how you would test for carbonate ions, CO₃²⁻ - Answer -✔✔Add nitric acid and
see if carbon dioxide bubbles form
Describe the test for ammonia gas - Answer -✔✔Turns damp red litmus paper blue
State the expression for calculating % yield. (Triple science only!) - Answer -✔✔% yield
= (actual amount of products/theoretical amount of products) x100
Describe the chemical test for water - Answer -✔✔Add water to anhydrous copper(II)
sulfate which will change from white to blue if water is present
What is the symbol for a reversible reaction? - Answer -✔✔
The addition of water to anhydrous copper sulfate can be used to test for the presence
of water. The reaction is reversible. What is the word equation? Describe the colour
change. - Answer -✔✔anhydrous copper sulfate (white) + water <-> hydrated copper
sulfate (blue)
Ammonia and hydrogen chloride react together in a reversible reaction to produce a
white solid. What are the word and symbol equations? - Answer -✔✔ammonia +
hydrogen chloride <-> ammonium chloride NH₃ + HCl <-> NH₄Cl
State two features of a reaction that is in dynamic equilibrium - Answer -✔✔1) The rate
of the forward reaction is equal to the rate of the backward reaction. 2) There is no
overall change in concentrations.
Predict what will happen to the equilibrium position in the following reaction when the
pressure is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g) +
3H₂(g) ΔH = +210 kJ mol⁻1 - Answer -✔✔Equilibrium will move to the left because there
are fewer molecules on the left hand side
Predict what will happen to the equilibrium position in the following reaction when the
temperature is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g)
, + 3H₂(g) ΔH = +210 kJ mol⁻1 - Answer -✔✔Equilibrium will move to the right because
the forward reaction is endothermic
Predict what will happen to the rate of reaction in the following reaction when the
temperature and pressure is increased. Give a reason for your prediction: CH₄(g) +
H₂O(g) <-> CO(g) + 3H₂(g) ΔH = +210 kJ mol⁻1 - Answer -✔✔The rate will increase
Predict what will happen to the equilibrium position in the following reaction when the
temperature is increased. Give a reason for your prediction: CO(g) + H₂O(g) <-> CO₂(g)
+ H₂(g) ΔH = -42 kJ mol⁻1 - Answer -✔✔Equilibrium will move to left the because the
reaction is exothermic
Predict what will happen to the equilibrium position in the following reaction when the
temperature is decreased. Give a reason for your prediction: CO(g) + 2H₂(g) <->
CH₃OH(g) ΔH = -91 kJ mol⁻1 - Answer -✔✔Equilibrium will move to right the because
the reaction is exothermic
Predict what will happen to the equilibrium position in the following reaction when the
pressure is decreased. Give a reason for your prediction: CO(g) + 2H₂(g) <-> CH₃OH(g)
ΔH = -91 kJ mol⁻1 - Answer -✔✔Equilibrium will move to left the because there are
more molecules on the left hand side
State the raw materials used in the manufacture of ammonia - Answer -✔✔nitrogen
from air and hydrogen from natural gas
State a use for N₂ - Answer -✔✔making ammonia
The following reaction is used to manufacture ammonia in the Haber process: N₂ + 3H₂
-> 2NH₃ ΔH = -92KJ/mol. The reaction is carried out at 450⁰C but the reaction would be
faster if a higher temperature were used. Suggest why a higher temperature is not used
in the Haber process - Answer -✔✔Yield would decrease and energy costs would
increase
State the temperature used for the manufacture of ammonia by the Haber process -
Answer -✔✔450°C
State the pressure used for the manufacture of ammonia by the Haber process -
Answer -✔✔200 atm
State the catalyst used for the manufacture of ammonia by the Haber process - Answer
-✔✔Iron
Answer Update 2025
State the method used to obtain sand from a mixture of sand and water - Answer -
✔✔filtration
State the method used to obtain solid copper sulfate from aqueous copper sulfate -
Answer -✔✔crystallisation
State the method used to obtain red food dye from a mixture of food dyes - Answer -
✔✔paper chromatography
State the method used to obtain water from salt water - Answer -✔✔simple distillation
Draw a diagram to show equipment used in simple distillation - Answer -✔✔For what
process is this equipment used?
State the method used to obtain kerosene from a crude oil. - Answer -✔✔fractional
distillation
Draw the equipment used in fractional distillation in the lab - Answer -✔✔For what
process is this equipment used?
Explain how fractional distillation is used to separate a mixture of different liquids -
Answer -✔✔The different liquids have different boiling points
State the method used to extract the red dye from a sample of rose petals - Answer -
✔✔dissolving
Describe how pure salt can be obtained from rock salt - Answer -✔✔1) Grind rock salt
into a fine powder. 2) Add powder to hot water and stir to dissolve salt. 3) Filter mixture.
Salt solution passes through the filter paper leaving behind the sand. 4) Boil filtrate to
evaporate some of the water. 5) Leave saturated solution to cool so that crystals of salt
form. 6) Filter cold mixture to separate the crystals from the remaining solution.
Ethanol is a flammable liquid. Suggest how it could be heated safely - Answer -✔✔Use
a water bath
Explain how a chromatogram shows that different dyes are different from each other -
Answer -✔✔Each dyes has a different mixture
,State the expression for calculating molar concentration - Answer -✔✔Molar
concentration = Amount (in moles)/volume (in dm^³)
Which cation gives a crimson red flame colour? - Answer -✔✔Li⁺
Which cation gives a orange flame colour? - Answer -✔✔Na⁺
Which cation gives a lilac flame colour? - Answer -✔✔K⁺
Which cation gives a brick red flame colour? - Answer -✔✔Ca²⁺
Describe how you would carry out a flame test - Answer -✔✔Put solid onto a wire. Put
into a blue flame
How would you test for the ammonium ion? - Answer -✔✔Add sodium hydroxide. If
ammonium ions were present, ammonia gas will form which will turn damp red litmus
paper blue
Describe how you would test for Cu²⁺ ions - Answer -✔✔Add sodium hydroxide and a
blue precipitate will form
Give the formula of the blue precipitate formed when sodium hydroxide is added to a
solution containing Cu²⁺ - Answer -✔✔Cu(OH)₂
Describe how you would test for Fe²⁺ ions - Answer -✔✔Add sodium hydroxide and a
green precipitate will form
Write a word equation for the reaction between sodium hydroxide and iron(II) sulfate -
Answer -✔✔sodium hydroxide + iron(II) sulfate -> iron (II) hydroxide + sodium sulfate
Describe how you would test for Fe³⁺ ions - Answer -✔✔Add sodium hydroxide and a
brown precipitate will form
What 2 things are added to a solution to test for chloride ions? What is observed if they
are present? - Answer -✔✔Add dilute nitric acid and silver nitrate. A white precipitate of
silver chloride is formed.
Describe the test for bromide ions. - Answer -✔✔Add dilute nitric acid and silver nitrate.
A cream precipitate of silver bromide is formed.
After adding nitric acid and silver nitrate to a solution containing iodide ions, what colour
precipitate is formed? - Answer -✔✔A yellow precipitate (of silver iodide) is formed.
,Why is hydrochloric acid added before barium chloride solution in testing for sulfate
ions? - Answer -✔✔To remove carbonate ions
Describe how you would test for sulfate ions - Answer -✔✔Add dilute HCl, followed by
BaCl₂. A white precipitate will form
Write an chemical equation for the reaction between barium chloride and lithium sulfate
(Li₂SO₄). Include state symbols. Also, what would you see? - Answer -✔✔BaCl₂ (aq) +
Li₂SO₄ (aq) -> BaSO₄ (s)+ 2LiCl (aq). Observe a white precipitate of barium sulfate.
Describe how you would test for carbonate ions, CO₃²⁻ - Answer -✔✔Add nitric acid and
see if carbon dioxide bubbles form
Describe the test for ammonia gas - Answer -✔✔Turns damp red litmus paper blue
State the expression for calculating % yield. (Triple science only!) - Answer -✔✔% yield
= (actual amount of products/theoretical amount of products) x100
Describe the chemical test for water - Answer -✔✔Add water to anhydrous copper(II)
sulfate which will change from white to blue if water is present
What is the symbol for a reversible reaction? - Answer -✔✔
The addition of water to anhydrous copper sulfate can be used to test for the presence
of water. The reaction is reversible. What is the word equation? Describe the colour
change. - Answer -✔✔anhydrous copper sulfate (white) + water <-> hydrated copper
sulfate (blue)
Ammonia and hydrogen chloride react together in a reversible reaction to produce a
white solid. What are the word and symbol equations? - Answer -✔✔ammonia +
hydrogen chloride <-> ammonium chloride NH₃ + HCl <-> NH₄Cl
State two features of a reaction that is in dynamic equilibrium - Answer -✔✔1) The rate
of the forward reaction is equal to the rate of the backward reaction. 2) There is no
overall change in concentrations.
Predict what will happen to the equilibrium position in the following reaction when the
pressure is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g) +
3H₂(g) ΔH = +210 kJ mol⁻1 - Answer -✔✔Equilibrium will move to the left because there
are fewer molecules on the left hand side
Predict what will happen to the equilibrium position in the following reaction when the
temperature is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g)
, + 3H₂(g) ΔH = +210 kJ mol⁻1 - Answer -✔✔Equilibrium will move to the right because
the forward reaction is endothermic
Predict what will happen to the rate of reaction in the following reaction when the
temperature and pressure is increased. Give a reason for your prediction: CH₄(g) +
H₂O(g) <-> CO(g) + 3H₂(g) ΔH = +210 kJ mol⁻1 - Answer -✔✔The rate will increase
Predict what will happen to the equilibrium position in the following reaction when the
temperature is increased. Give a reason for your prediction: CO(g) + H₂O(g) <-> CO₂(g)
+ H₂(g) ΔH = -42 kJ mol⁻1 - Answer -✔✔Equilibrium will move to left the because the
reaction is exothermic
Predict what will happen to the equilibrium position in the following reaction when the
temperature is decreased. Give a reason for your prediction: CO(g) + 2H₂(g) <->
CH₃OH(g) ΔH = -91 kJ mol⁻1 - Answer -✔✔Equilibrium will move to right the because
the reaction is exothermic
Predict what will happen to the equilibrium position in the following reaction when the
pressure is decreased. Give a reason for your prediction: CO(g) + 2H₂(g) <-> CH₃OH(g)
ΔH = -91 kJ mol⁻1 - Answer -✔✔Equilibrium will move to left the because there are
more molecules on the left hand side
State the raw materials used in the manufacture of ammonia - Answer -✔✔nitrogen
from air and hydrogen from natural gas
State a use for N₂ - Answer -✔✔making ammonia
The following reaction is used to manufacture ammonia in the Haber process: N₂ + 3H₂
-> 2NH₃ ΔH = -92KJ/mol. The reaction is carried out at 450⁰C but the reaction would be
faster if a higher temperature were used. Suggest why a higher temperature is not used
in the Haber process - Answer -✔✔Yield would decrease and energy costs would
increase
State the temperature used for the manufacture of ammonia by the Haber process -
Answer -✔✔450°C
State the pressure used for the manufacture of ammonia by the Haber process -
Answer -✔✔200 atm
State the catalyst used for the manufacture of ammonia by the Haber process - Answer
-✔✔Iron
