IGCSE · Practice questions · Insoluble salts and solubility rules

Predict the precipitate.

Six original Cambridge-style questions on solubility rules and the preparation of insoluble salts by precipitation.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Know the exceptions.

Always soluble: Na, K, NH₄ compounds and all nitrates.
Chlorides: not Ag, Pb. Sulfates: not Ba, Ca, Pb.
Carbonates, hydroxides: insoluble except Na, K, NH₄.
Precipitation: mix, filter, wash residue, dry.

Recall

[4 marks]

State whether each compound is soluble or insoluble in water: (a) lead(II) nitrate, (b) calcium carbonate, (c) potassium sulfate, (d) silver chloride.

(a) soluble ✓
(b) insoluble ✓
(c) soluble ✓
(d) insoluble ✓

Recall

[4 marks]

(Extended) Describe how to prepare a pure, dry sample of barium sulfate.

Mix aqueous barium chloride (or barium nitrate) with aqueous sodium sulfate (or dilute sulfuric acid). ✓
A white precipitate of barium sulfate forms. ✓
Filter the mixture and wash the residue with distilled water. ✓
Dry the residue in a warm oven or between filter papers. ✓

Analysis

[2 marks]

(Extended) Name two solutions that could be mixed to make lead(II) iodide, and describe what is seen.

Lead(II) nitrate solution and potassium iodide (or sodium iodide) solution. ✓
A yellow precipitate forms. ✓

Recall

[2 marks]

(Extended) Write the ionic equation, with state symbols, for the precipitation of barium sulfate.

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) ✓
One mark for the correct ions and product, one for state symbols. ✓

Explain

[2 marks]

(Extended) Explain why lead(II) nitrate, rather than lead(II) carbonate, is used as the source of lead ions when preparing lead(II) iodide.

Lead(II) nitrate is soluble, so it provides Pb²⁺ ions in solution. ✓
Lead(II) carbonate is insoluble, so its lead ions are not free to react. ✓

Analysis

[2 marks]

Predict whether a precipitate forms when each pair of solutions is mixed: (a) sodium carbonate and calcium chloride, (b) potassium nitrate and sodium chloride.

(a) yes: insoluble calcium carbonate precipitates. ✓
(b) no: every possible product (potassium chloride, sodium nitrate) is soluble. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.