Calcium ions and aluminium ions both give a white precipitate with sodium hydroxide solution. How can they be told apart?

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Question

Calcium ions and aluminium ions both give a white precipitate with sodium hydroxide solution. How can they be told apart?

Accepted Answer

Add excess sodium hydroxide solution, in which aluminium hydroxide dissolves — Award 1 mark. Aluminium hydroxide is amphoteric and redissolves to give a colourless solution, while calcium hydroxide stays as a white solid.

Answer

The two ions cannot be distinguished by any test

Answer

Both precipitates dissolve in excess, so timing is used instead

Answer

Add excess sodium hydroxide solution, in which aluminium hydroxide dissolves

Answer

Add excess sodium hydroxide solution, in which calcium hydroxide dissolves

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