This guide covers IGCSE Chemistry topic 8 (part 2): preparation of salts. You will revise soluble salts (acid + metal; acid + insoluble base; acid + carbonate; titration) and insoluble salts (precipitation); filtration, crystallisation, titration method.

Key concepts to revise

• Soluble salt – Acid + metal (if metal above H in reactivity); acid + insoluble base (e.g. CuO); acid + carbonate; or titration (acid + alkali) for soluble salts.
• Insoluble salt – Precipitation: mix two solutions that contain the ions of the salt (e.g. AgNO3 + NaCl → AgCl precipitate).
• Titration – Find exact volume of alkali to neutralise acid; use indicator; repeat for concordant results; then use exact volumes (no indicator) to make pure salt; crystallise.
• Filtration and crystallisation – Filter to remove excess solid or precipitate; evaporate and cool to crystallise soluble salt.

Exam tips and command words

• Describe – How to prepare a soluble salt (e.g. copper sulfate from acid + copper oxide: add base until in excess; filter; crystallise).
• Describe – How to prepare an insoluble salt (mix solutions of the two ions; filter; wash; dry).
• State – Why excess solid is used (to ensure all acid reacts); why indicator is not used when making the salt (would contaminate).
• Explain – Why titration is used for soluble salts from acid + alkali (to get exact ratio; pure salt).

Common mistakes

• Using soluble base (e.g. NaOH) without titration to make salt (would need titration; otherwise excess base contaminates).
• Saying “filter the salt” for soluble salt (you filter to remove excess solid; the filtrate contains the salt).
• Not stating that for insoluble salt you wash the precipitate (to remove other ions).

Revision checklist

• Describe how to prepare a soluble salt from acid + insoluble base (excess base; filter; crystallise).
• Describe how to prepare an insoluble salt by precipitation (mix solutions; filter; wash; dry).
• Describe the titration method for preparing a soluble salt from acid + alkali.
• State why excess solid is used and why the mixture is filtered.

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise salt preparation questions, or explore Tutopiya’s learning portal for more revision resources.

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