CIE IGCSE Chemistry

Topic Questions

IGCSEChemistryCIETopic Questions7. Acids, Bases & Salts7.2 Preparation of Salts

7.2 Preparation of Salts

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16 marks

The salt copper(II) sulphate can be prepared by reacting copper(II) oxide with sulphuric acid.

Complete the list of instructions for making copper(II) sulphate using six of the words below.

blue cool dilute  filter
saturated sulfate oxide white

Instructions

1
Add excess copper(II) oxide to .............................. sulphuric acid in a beaker and boil it.

2
.............................. to remove the unreacted copper(II) oxide.

3
Heat the solution until it is ..............................

4
.............................. the solution to form .............................. coloured crystals of copper(II) ..............................

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2a2 marks

Aqueous sodium hydroxide, NaOH(aq), is a strong alkali that reacts with dilute sulfuric acid exothermically.


Complete the equation for the reaction between aqueous sodium hydroxide and dilute sulfuric acid.

                         
 2NaOH + H2SO4 → ......................... + .........................


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2b1 mark

A student investigates the rate of reaction of small pieces of calcium carbonate with an excess of hydrochloric acid of concentration 1 mol / dm3.

                                  CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)

Name the salt formed when calcium carbonate reacts with hydrochloric acid.

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2c3 marks

Describe how you could prepare a  pure sample of crystals of hydrated zinc sulfate using dilute sulfuric acid and an excess of zinc.

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2d1 mark

A student investigates the rate of reaction of large pieces of magnesium carbonate with an excess of dilute nitric acid.

 
MgCO3 + 2HNO3 → Mg(NO3)2 + CO2 + H2O
 

Name the salt formed when magnesium carbonate reacts with dilute nitric acid.

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3a3 marks

This question is about cobalt and compounds of cobalt.

Describe how you could prepare a  pure sample of crystals of hydrated cobalt(II) sulfate using dilute sulfuric acid and an excess of cobalt(II) carbonate.

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3b1 mark

A student investigates the rate of reaction of magnesium ribbon with an excess of dilute hydrochloric acid.

Mg + 2HCl → MgCl2 + H2

Name the salt formed when magnesium reacts with dilute hydrochloric acid.

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4a1 mark

A student prepares crystals of magnesium chloride by adding an excess of magnesium carbonate to 50.00 cm3 of 2.00 mol / dm3 hydrochloric acid.
The student filters the mixture and rinses the residue.

Why does the student add an excess of magnesium carbonate?

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4b1 mark

Why does the student rinse the residue?

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4c3 marks

Describe how the student would obtain pure crystals of magnesium chloride from the filtrate.

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5a2 marks

Sulfuric acid has many uses.
Dilute sulfuric acid is used to make salts known as sulfates.
A method consisting of three steps is used to make zinc sulfate from zinc carbonate.
step 1   Add an excess of zinc carbonate to 20 cm3 of 0.4 mol / dm3 dilute sulfuric acid until the reaction is complete.
step 2   Filter the mixture.
step 3   Heat the filtrate until a saturated solution forms and then allow it to crystallise.


Suggest two observations which show that the reaction is complete in step 1.

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5b1 mark

State why it is important to add an excess of zinc carbonate in step 1.

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5c2 marks

Define the term saturated solution.

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5d1 mark

Name another zinc compound which can be used to make zinc sulfate from dilute sulfuric acid using this method.

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5e1 mark

Separate: Chemistry and Extended Only

Suggest why this method would not work to make barium sulfate from barium carbonate and dilute sulfuric acid.

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1a3 marks

Hydriodic acid, HI (aq), is a strong acid. Its salts are iodides.

It has the reactions of a typical strong acid. Complete the following equations.

 
i)
............Li + ............HI → ........................ + ...................

[1]

ii)
Zinc carbonate + hydriodic acid → .................... + .................... + ....................

[1]

iii)
MgO + ............HI → ................... + ...................

[1]

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1b2 marks

Two of the reactions in (a) are acid / base and one is redox. Which one is redox? Explain your choice.

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1c2 marks

Describe how you could distinguish between hydriodic, HI (aq), and hydrobromic, HBr (aq) acids, by bubbling chlorine through these two acids.

Result with hydriodic acid ..................................................................................................

 

Result with hydrobromic acid .......................................................................................

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1d5 marks

20.0 cm3 of aqueous sodium hydroxide, 2.00 mol / dm3, was placed in a beaker.

The temperature of the alkali was measured and 1.0 cm3 portions of hydriodic acid were added.

After each addition, the temperature of the mixture was measured. Typical results are shown on the graph.

cie-igcse-sq-7-2-sq-h-graph

NaOH (aq) + HI (aq) → NaI (aq) + H2O (l)

i)
Explain why the temperature increases rapidly at first and then stops increasing.

[2]

ii)
Suggest why the temperature drops after the addition of 18.0 cm3 of acid.

[1]

iii)
In another experiment, it was shown that 15.0 cm3 of the acid neutralised 20.0 cm3 of aqueous sodium hydroxide, 1.00 mol / dm3. Calculate the concentration of the acid.

[2]

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2a2 marks

The hydroxides of the Group I metals are soluble in water. Most other metal hydroxides are insoluble in water.

Crystals of lithium chloride can be prepared from lithium hydroxide by titration.

 

9N-OtS-d_titration

25.0cm3 of aqueous lithium hydroxide is pipetted into the conical flask.

A few drops of an indicator are added. Dilute hydrochloric acid is added slowly to the alkali until the indicator just changes colour. The volume of acid needed to neutralise the lithium hydroxide is noted.

A neutral solution of lithium chloride, which still contains the indicator, is left. Describe how you could obtain a neutral solution of lithium chloride which does not contain an indicator.

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2b
Sme Calculator2 marks

Separate: Chemistry and Extended Only

The concentration of the hydrochloric acid was 2.20 mol / dm3. The volume of acid needed to neutralise the 25.0 cm3 of lithium hydroxide was 20.0 cm3. Calculate the concentration of the aqueous lithium hydroxide.

 

LiOH + HCl → LiCl + H2O

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2c
Sme Calculator3 marks

Separate: Chemistry and Extended Only

Lithium chloride forms three hydrates. They are LiCl.H2O, LiCl.2H2O and LiCl.3H2O.
 

Which one of these three hydrates contains 45.9% of water? Show how you arrived at your answer.

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3a4 marks

Soluble salts can be made using a base and an acid.

Complete this method of preparing dry crystals of the soluble salt cobalt(II) chloride-6-water from the insoluble base cobalt(II) carbonate.

Step 1

Add an excess of cobalt(II) carbonate to hot dilute hydrochloric acid.

Step 2

............................................................................................................

Step 3

............................................................................................................

 
Step 4
............................................................................................................

[4]

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3b
Sme Calculator6 marks

Separate: Chemistry and Extended Only

5.95g of cobalt(II) carbonate were added to 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3.
 

i)
Calculate the maximum yield of cobalt(II) chloride-6-water and show that the cobalt(II)carbonate was in excess.
 
CoCO3 + 2HCl → CoCl2 + CO2 + H2O
CoCl2 + 6H2O → CoCl2.6H2O
 
Maximum yield:
number of moles of HCl used = ..............................
number of moles of CoCl2 formed = ..............................
number of moles of CoCl2.6H2O formed = ..............................
mass of one mole of CoCl2.6H2O = 238 g
maximum yield of CoCl2.6H2O = .............................. g
 
To show that cobalt(II) carbonate is in excess:
number of moles of HCl used = .............................. (use your value from above)
mass of one mole of CoCO3 = 119g
number of moles of CoCO3 in 5.95g of cobalt(II) carbonate = ..............................

[5]

ii)
Explain how these calculations show that cobalt(II) carbonate is in excess.
[1] 

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4a2 marks

Silver(I) chromate(VI) is an insoluble salt. It is prepared by precipitation. 20 cm3 of aqueous silver(I) nitrate, concentration 0.2 mol /dm3, was mixed with 20 cm3 of aqueous potassium chromate(VI), concentration 0.1 mol /dm3. After stirring, the mixture was filtered. The precipitate was washed several times with distilled water. The precipitate was then left in a warm oven for several hours.

2AgNO3 (aq) + K2CrO4 (aq) → Ag2CrO4 (s) + 2KNO3 (aq)

What difficulty arises if the name of a compound of a transition element does not include its oxidation state, for example iron oxide?

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4b3 marks

Extended Only

These questions refer to the preparation of the salt.

i)
Why is it necessary to filter the mixture after mixing and stirring?
[1]

ii)
What is the purpose of washing the precipitate?
[1]

iii)
Why leave the precipitate in a warm oven?
[1]

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4c
Sme Calculator6 marks

Separate: Chemistry and Extended Only

i)
Explain why the concentrations of silver(I) nitrate and potassium chromate(VI) are different.
[1]

ii)
What mass of silver(I) nitrate is needed to prepare 100 cm3 of silver(I) nitrate solution, concentration 0.2 mol / dm3?

The mass of one mole of AgNO3 is 170 g.
[2]

iii)
What is the maximum mass of silver(I) chromate(VI) which could be obtained from 20 cm3 of aqueous silver(I) nitrate, concentration 0.2 mol / dm3?

Number of moles of AgNO3 used = .....................
[1]
Number of moles of Ag2CrO4 formed = .....................
[1]
Mass of one mole of Ag2CrO4 = 332 g
 
Mass of Ag2CrO4 formed = ..................... g
[1]

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5a5 marks

Extended Only

Insoluble salts are made by precipitation.

A preparation of the insoluble salt calcium fluoride is described below.


To 15 cm3 of aqueous calcium chloride, 30 cm3 of aqueous sodium fluoride is added. The concentration of both solutions is 1.00 mol / dm3. The mixture is filtered and the precipitate washed with distilled water. Finally, the precipitate is heated in an oven.

i)
Complete the equation.

Ca2+ + ..........F- →...............

[2]

ii)
Why is the volume of sodium fluoride solution double that of the calcium chloride solution?

[1]

iii)
Why is the mixture washed with distilled water?

[1]

iv)
Why is the solid heated?

[1]

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5b3 marks

Extended Only

The formulae of insoluble compounds can be found by precipitation reactions. To 12.0 cm3 of an aqueous solution of the nitrate of metal T was added 2.0 cm3 of aqueous sodium phosphate, Na3PO4. The concentration of both solutions was 1.00 mol/ dm3.

When the precipitate had settled, its height was measured.

screen-shot-2022-09-07-at-15-50-55


The experiment was repeated using different volumes of the phosphate solution. The results are shown on the following graph.

 
t3po4-graph-cie

 
What is the formula of the phosphate of metal T? Give your reasoning.

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1a5 marks

Soluble salts can be made by the neutralisation of an acid by a base. Insoluble salts can be made by precipitation.

The following is a brief description of the preparation of the soluble salt, nickel(II) chloride-6-water, from the insoluble base nickel(II) carbonate. Nickel(II) carbonate is added in small amounts to hot dilute hydrochloric acid until it is in excess. The mixture is filtered. The filtrate is partially evaporated and then allowed to cool until crystals of nickel(II) chloride-6-water form.

i)
Why is it necessary to use excess carbonate?

[1]

ii)
Explain why it is necessary to filter.

[1]

iii)
Why partially evaporate rather than evaporate to dryness?

[1]

iv)
What additional steps are needed to obtain dry crystals?

[2]

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1b5 marks

Separate: Chemistry Only

Potassium chloride can be made from hydrochloric acid and potassium carbonate.

i)
Why must a different experimental method be used for this preparation?

[1]

ii)
Give a description of the different method used for this salt preparation.

[4]

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1c
Sme Calculator5 marks

Separate: Chemistry and Extended Only

Insoluble salts are made by precipitation. An equation for the preparation of barium sulfate is given below.


BaCl2 (aq) + MgSO4 (aq) → BaSO4 (s) + MgCl2 (aq)

This reaction can be used to find x in the formula for hydrated magnesium sulfate MgSO4.xH2O. 


A known mass of hydrated magnesium sulfate, MgSO4.xH2O, was dissolved in water. Excess aqueous barium chloride was added. The precipitate of barium sulfate was filtered, washed and dried. Finally it was weighed.

Mass of hydrated magnesium sulfate = 1.476 g
Mass of barium sulfate formed = 1.398 g
The mass of one mole of BaSO4 = 233 g

The number of moles of BaSO4 formed = ...............

[1]

The number of moles of MgSO4.xH2O = ...............

[1]

The mass of one mole of MgSO4.xH2O = ...............g

[1]

The mass of one mole of MgSO4= 120 g

The mass of xH2O in one mole of MgSO4.xH2O = ...............

[1]

x = ...............

[1]

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2a3 marks

Three common methods of preparing salts are shown below.

method A adding an excess of an insoluble base or carbonate or metal to a dilute acid and removing excess by filtration
method B using a burette and indicator
method C mixing two solutions to obtain the salt by precipitation

For each of the following salt preparations, choose a method, A, B or C. Name any additional reagent which is needed and complete the equation.

The soluble salt, nickel chloride, from the insoluble compound nickel carbonate

method .......................................................................................................................................

reagent ......................................................................................................................................

word equation ............................................................................................................................

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2b3 marks

Separate: Chemistry and Extended Only

The insoluble salt, lead(II) bromide, from aqueous lead(II) nitrate

method .......................................................................................................................................

reagent ......................................................................................................................................

ionic equation ........ + ........ → PbBr2

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2c4 marks

The soluble salt, lithium sulfate, from the soluble base lithium hydroxide

method .......................................................................................................................................

reagent ......................................................................................................................................

equation .....................................................................................................................................

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3a6 marks

Extended Only

Three ways of making salts are

  • titration using a soluble base or carbonate
  • neutralisation using an insoluble base or carbonate
  • precipitation

Complete the following table of salt preparations.

Method Reagent 1 Reagent 2 Salt
Titration

.............................

.............................

.............................

.............................

 Sodium nitrate
Neutralisation

Nitric acid 

.............................

.............................

 Copper(II) nitrate
Precipitation

.............................

.............................

.............................

.............................

 Silver(I) chloride 
Neutralisation 

Sulfuric acid 

Zinc(II) carbonate

.............................

.............................

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3b4 marks
i)
Write an ionic equation with state symbols for the preparation of silver(I) chloride.

[2]

ii)
Complete the following equation.

ZnCO3 + H2SO4 → ............... + ............... + ...............

[2]

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4a2 marks

Chlorine reacts with phosphorus to form phosphorus trichloride.

Draw a diagram showing the arrangement of the outer electrons in one molecule of the covalent compound, phosphorus trichloride.

Use x to represent an electron from a phosphorus atom.
Use o to represent an electron from a chlorine atom.

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4b8 marks

Extended Only

Phosphorus trichloride reacts with water to form two acids.

i)
Balance the equation for this reaction.

PCl3 + .......H2O → .......HCl + H3PO3

[1]

ii)
Describe how you could show that phosphorus acid, H3PO3, is a weaker acid than hydrochloric acid.
[3]

iii)
Two salts of phosphorus acid are its sodium salt, which is soluble in water, and its calcium salt which is insoluble in water. Suggest a method of preparation for each of these salts from aqueous phosphorus acid. Specify any other reagent needed and briefly outline the method.

Sodium salt

[2]

   Calcium salt

[2]

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5a6 marks

Oxides are classified as acidic, basic, neutral and amphoteric.

Complete the table.

Type of oxide pH of solution of oxide Example
Acidic     
Basic    
Neutral    

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5b3 marks

Extended Only

i)
Explain the term amphoteric.
[1]

ii)
Name two reagents that are needed to show that an oxide is amphoteric.
[2]

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610 marks

Extended Only

There are three methods of preparing salts.

  • Method A – use a burette and an indicator.
  • Method B – mix two solutions and obtain the salt by precipitation.
  • Method C – add an excess of base or a metal to a dilute acid and remove the excess by filtration.

For each of the following salt preparations, choose one of the methods A, B or C, name any additional reagent needed and then write or complete the equation.

 
i)
The soluble salt, zinc sulfate, from the insoluble base, zinc oxide
 
method ..................................................
 
reagent ..................................................
 
word equation ..................................................
[3]
ii)
The soluble salt, potassium chloride, from the soluble base, potassium hydroxide
 
method ..................................................
reagent ..................................................
 
equation ..................... + .....................  → KCl + H2O
[3]

iii)
The insoluble salt, lead(II) iodide, from the soluble salt, lead(II) nitrate
 
method ..................................................
 
reagent ..................................................
 
equation Pb2+ + ..................... → ..................... 
[4]

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7a1 mark

Separate: Chemistry Only

Which one of these salts is soluble in water?
Tick one box.

barium sulfate  
calcium carbonate  
ammonium sulfate  
iron(II) hydroxide  


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7b1 mark

Carbon dioxide is a gas.

Which one of these processes does not produce carbon dioxide?

Tick one box.

the reaction of hydrochloric acid with calcium carbonate  
the complete combustion of carbon-containing fuels  
the reaction of hydrochloric acid with magnesium  
the thermal decomposition of calcium carbonate  

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7c2 marks

Concentrated sulfuric acid is a dehydrating agent which can chemically remove water from substances.

Both hydrated copper(II) sulfate crystals and sucrose (a sugar), C12H22O11, can be completely dehydrated by concentrated sulfuric acid.


Name the solid product formed in each case.


hydrated copper(II) sulfate crystals ________________

sucrose ________________

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7d3 marks

This question is about copper and copper compounds.

Describe how you could prepare a pure sample of crystals of hydrated copper(II) sulfate using dilute sulfuric acid and an excess of copper(II) oxide.

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8a2 marks

Extended Only

Silver chloride, AgCl, is insoluble. It can be made by a precipitation reaction between aqueous barium chloride and a suitable aqueous silver salt.


What is meant by the term precipitate?

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8b3 marks

Separate: Chemistry and Extended Only

Name a suitable silver salt to use to prepare silver chloride.

Complete the chemical equation to show the formation of insoluble silver chloride from aqueous barium chloride and the silver salt you have named.

name of a suitable silver salt ...........................................

BaCl2 + ..................... rightwards arrow ..................... + .....................

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