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