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2017 O Level Chem P1 Q2 — Salts / Precipitation Reactions Solution

Salts / Precipitation Reactions 2017 O Level Pure Chemistry · Paper 1 · Q2

Question

In which reaction is a white precipitate formed?

Aacidified potassium manganate(VII) + sulfur dioxide
Baqueous barium nitrate + aqueous potassium chloride
Caqueous calcium hydroxide + carbon dioxide
Daqueous copper(II) sulfate + aqueous sodium hydroxide

Correct answer: C

Video Solution

Explanation

Answer: C. Aqueous calcium hydroxide (limewater) reacts with carbon dioxide to form a white precipitate of calcium carbonate: \(\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}\).

A gives a colour change (purple to colourless), not a precipitate. B gives no precipitate (barium chloride and potassium nitrate are both soluble). D gives a blue precipitate of copper(II) hydroxide, not white.

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