Chemistry Tuition Singapore O Level Chemistry Tuition- Salts Common Misconception

Misconception 1

On adding ammonia solution to aqueous copper(II) sulfate, a soluble blue precipitate is formed. (Comment: The error is the phrase “soluble precipitate”.)

Correct Conception 1

On adding ammonia solution to aqueous copper(II) sulfate, a light blue precipitate is formed. The precipitate dissolves in excess ammonia solution.

Misconception 2

All metal ions react with aqueous sodium hydroxide to form precipitates.

Correct Conception 2

Metal ions, such as Na+ and KE, do not form precipitates with NaOH(aq).

Misconception 3

To test for Cl^– ions, add hydrochloric acid, followed by silver nitrate solution.

Correct Conception 3

HC1(aq) should not be used, as Cl^– ion from HCI(aq) will give a white precipitate with AgNO₃(aq). Dilute nitric acid should be used to acidify AgNO₃(aq).

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