Tests for Metal Ions in Solution (Cations) Flashcards

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Which solution is commonly added to test for metal ions (cations) in solution?

Sodium hydroxide solution is commonly added to test for metal ions in solution.

What do you look for when sodium hydroxide is added to a solution containing metal ions?

You look for a solid precipitate and its colour, which help to identify the metal ion.

What is a precipitate in the test for metal ions?

A precipitate is a solid that forms when two solutions react and the solid does not dissolve in water.

What happens when sodium hydroxide is added to a solution containing aluminium ions (Al3+)?

A white precipitate of aluminium hydroxide forms, which dissolves in excess sodium hydroxide to give a colourless solution.

What happens when sodium hydroxide is added to a solution containing calcium ions (Ca2+)?

A white precipitate of calcium hydroxide forms, and it does not dissolve in excess sodium hydroxide.

What colour precipitate forms when sodium hydroxide is added to a solution containing copper(II) ions (Cu2+)?

A blue precipitate of copper(II) hydroxide forms.

What colour precipitate forms when sodium hydroxide is added to a solution containing iron(II) ions (Fe2+)?

A green precipitate of iron(II) hydroxide forms.

What colour precipitate forms when sodium hydroxide is added to a solution containing iron(III) ions (Fe3+)?

A brown precipitate of iron(III) hydroxide forms.

How can you tell aluminium ions (Al3+) apart from calcium ions (Ca2+) using sodium hydroxide?

Add excess sodium hydroxide: the white aluminium hydroxide precipitate dissolves, but the white calcium hydroxide precipitate does not.

Why are the colours of metal hydroxide precipitates useful in chemistry?

Each metal ion gives a specific precipitate colour, so you can use the colour to identify which metal ion is present.