7.3

Preparation of salts

Cambridge IGCSE Chemistry (0620)  · Unit 7: Acids, bases and salts  · 12 flashcards

Preparation of salts is topic 7.3 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 7 — Acids, bases and salts , alongside Acids and bases, Reactions of acids and Oxides.  In one line: A hydrated substance is a substance that is chemically combined with water.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).

The deck below contains 12 flashcards — 3 definitions, 3 key concepts and 6 identification cards — covering the precise wording mark schemes reward.  Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

A hydrated substance

A hydrated substance is a substance that is chemically combined with water.

Example: Copper(II) sulfate pentahydrate (CuSO₄·5H₂O).

What the Cambridge 0620 syllabus says

2026-2028 syllabus, in our words

What the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).

  1. Describe Describe how to make a soluble salt, then separate and purify it, by reacting an acid with: an alkali (using titration), an excess of a metal, an excess of an insoluble base, or an excess of an insoluble carbonate.
  2. Describe Describe the general rules for which salts dissolve: all nitrates and all salts of sodium, potassium and ammonium are soluble; chlorides are soluble apart from those of lead and silver; sulfates are soluble apart from barium, calcium and lead sulfates; carbonates are insoluble apart from sodium, potassium and ammonium carbonates; hydroxides are insoluble apart from sodium, potassium and ammonium hydroxides, with calcium hydroxide partly soluble.
  3. Define Define the terms hydrated (a substance with water chemically combined in it) and anhydrous (a substance that contains no water).
  4. Describe Describe how an insoluble salt is made by precipitation. Supplement
  5. Define Define water of crystallisation: the H₂O molecules contained within hydrated crystals, such as those of CuSO₄·5H₂O and CoCl₂·6H₂O. Supplement
Key Concept Flip

Describe the general method to prepare a soluble salt by reacting an acid with an insoluble base, carbonate, or metal.

Answer Flip

Add the solid (base, carbonate, or metal) in excess to the acid. Warm the mixture. Filter off the excess solid. Heat the solution to evaporate the water and crystallise the salt.

Example: CuO + H2SO4 -> CuSO4 + H2O.
Key Concept Flip

Describe the general method to prepare a soluble salt by reacting an acid with an alkali using titration.

Answer Flip

Use a pipette to measure a known volume of the alkali into a conical flask. Add a few drops of indicator. Slowly add acid from a burette, swirling the flask, until the indicator shows the endpoint. Repeat without indicator. Heat to evaporate water until crystallisation point.

Example: NaOH + HCl -> NaCl + H2O.
Key Concept Flip

Give the general solubility rule for Sodium, Potassium, and Ammonium salts.

Answer Flip

Sodium, potassium, and ammonium salts are soluble.

Example: sodium chloride (NaCl) is soluble in water.
Key Concept Flip

Give the general solubility rule for Nitrates.

Answer Flip

Nitrates are soluble.

Example: potassium nitrate (KNO3) is soluble in water.
Key Concept Flip

Give the general solubility rule for Chlorides.

Answer Flip

Chlorides are soluble, except for lead chloride (PbCl₂) and silver chloride (AgCl).

Key Concept Flip

Give the general solubility rule for Sulfates.

Answer Flip

Sulfates are soluble, except for barium sulfate (BaSO₄), calcium sulfate (CaSO₄), and lead sulfate (PbSO₄).

Key Concept Flip

Give the general solubility rule for Carbonates.

Answer Flip

Carbonates are insoluble, except for sodium carbonate (Na₂CO₃), potassium carbonate (K₂CO₃), and ammonium carbonate ((NH₄)₂CO₃).

Key Concept Flip

Give the general solubility rule for Hydroxides.

Answer Flip

Hydroxides are insoluble, except for sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH₄OH), and calcium hydroxide (Ca(OH)₂ - partially soluble).

Definition Flip

Define a hydrated substance.

Answer Flip

A hydrated substance is a substance that is chemically combined with water.

Example: Copper(II) sulfate pentahydrate (CuSO₄·5H₂O).
Definition Flip

Define an anhydrous substance.

Answer Flip

An anhydrous substance is a substance containing no water.

Example: Anhydrous copper(II) sulfate (CuSO₄).
Key Concept Flip

Describe the preparation of insoluble salts by precipitation.

Answer Flip

Mix two solutions containing soluble salts that will form the insoluble salt. Filter the mixture to collect the precipitate. Wash the precipitate with distilled water to remove any soluble impurities. Dry the precipitate.

Example: Pb²⁺(aq) + SO₄²⁻(aq) → PbSO₄(s).
Definition Flip

Define the term 'water of crystallisation'.

Answer Flip

Water of crystallisation refers to the water molecules present in hydrated crystals.

Example: CuSO₄.5H₂O contains 5 molecules of water of crystallisation.

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7.2 Reactions of acids 7.4 Oxides

Key Questions: Preparation of salts

Define a hydrated substance.

A hydrated substance is a substance that is chemically combined with water.

Example: Copper(II) sulfate pentahydrate (CuSO₄·5H₂O).
Define an anhydrous substance.

An anhydrous substance is a substance containing no water.

Example: Anhydrous copper(II) sulfate (CuSO₄).
Define the term 'water of crystallisation'.

Water of crystallisation refers to the water molecules present in hydrated crystals.

Example: CuSO₄.5H₂O contains 5 molecules of water of crystallisation.

More topics in Unit 7 — Acids, bases and salts

Preparation of salts sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

7.1 Acids and bases

19 flashcards
7.2 Reactions of acids

10 flashcards
7.4 Oxides

10 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

salt soluble salt insoluble salt crystallisation precipitation filtration evaporation titration excess washing drying

Key terms covered in this Preparation of salts deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

A hydrated substance
An anhydrous substance
The term 'water of crystallisation'

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