Free Preparation of salts questions for IGCSE Chemistry (0620), part of Acids, bases & salts. Each question has the answer and the marking points an examiner would look for.
Generate a full Preparation of Salts worksheet →All Acids, bases & salts questionsWhich method is used to make a pure sample of zinc chloride crystals?
Answer: C
Which term is described by this statement?
“A compound formed when the hydrogen of an acid is replaced by a metal or ammonium ion.”
Answer: B
Which method is used to make a pure sample of sodium nitrate crystals?
Answer: C
A student wants to make pure, dry crystals of zinc sulfate, ZnSO4•7H2O, from zinc oxide and dilute sulfuric acid.
Describe how the student should make the crystals. Give the reasons for the key steps.
Write the equation for the reaction, with state symbols.
Explain why the student does not heat the solution to dryness.
Explain why this method cannot be used to make barium sulfate, and name a suitable method.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | Warm acid, add zinc oxide a little at a time until in excess (no more dissolves); filter to remove excess zinc oxide; heat the filtrate to evaporate some water until saturated (crystals form on a glass rod); leave to cool and crystallise; filter/pick out crystals, wash with a little cold water and dry between filter papers add zinc oxide to (warm) acid until in excess / no more dissolves B1 reason: to make sure all the acid is used up B1 filter to remove excess zinc oxide B1 heat filtrate to point of crystallisation (not to dryness) B1 cool / leave to crystallise B1 separate crystals and dry with filter paper / in a warm place B1 | 6 |
| (b) | ZnO(s) + H2SO4(aq) → ZnSO4(aq) + H2O(l) correct formulae, balanced B1 correct state symbols B1 | 2 |
| (c) | Water of crystallisation would be lost / the hydrated crystals would decompose water of crystallisation lost / crystals would not be hydrated B1 | 1 |
| (d) | Barium sulfate is insoluble, so it cannot be crystallised from a solution; make it by precipitation from two soluble salts barium sulfate is insoluble B1 precipitation (mix solutions, filter, wash, dry) B1 | 2 |
A student wants to prepare pure, dry crystals of copper(II) sulfate from copper(II) oxide and dilute sulfuric acid.
Describe the method.
Explain why excess copper(II) oxide is used.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | excess base, filter, evaporate, crystallise warm the acid and add copper(II) oxide until it is in excess (no more dissolves) B1 filter to remove excess oxide B1 heat the filtrate to evaporate some water (to crystallisation point) B1 leave to cool and crystallise B1 filter/pat dry crystals with filter paper B1 | 5 |
| (b) | ensure all acid reacts to make sure all the acid is used up B1 | 1 |
Barium sulfate is an insoluble salt.
Name two solutions that could be mixed to make barium sulfate.
Name the method used to prepare insoluble salts.
Describe how the pure, dry salt is obtained from the mixture.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | barium chloride/nitrate + sodium sulfate/sulfuric acid barium chloride (or nitrate) B1 sodium sulfate (or sulfuric acid) B1 | 2 |
| (b) | precipitation precipitation B1 | 1 |
| (c) | filter, wash, dry filter B1 wash the residue with distilled water and dry B1 | 2 |
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