Tests for Cations Flashcards

All 7 cards in this deck

What do you see when sodium hydroxide solution is added to a solution containing copper ions, $\mathrm{Cu^{2+}}$?

A blue precipitate.

What do you see when sodium hydroxide solution is added to a solution containing iron(II) ions, $\mathrm{Fe^{2+}}$?

A green precipitate.
It slowly turns brown in air as $\mathrm{Fe^{2+}}$ is oxidised to $\mathrm{Fe^{3+}}$.

What do you see when sodium hydroxide solution is added to a solution containing iron(III) ions, $\mathrm{Fe^{3+}}$?

A brown precipitate.

What do you see when sodium hydroxide solution is added to a solution containing aluminium ions, $\mathrm{Al^{3+}}$?

A white precipitate that redissolves in excess sodium hydroxide solution to give a colourless solution.

What do you see when sodium hydroxide solution is added to a solution containing calcium ions, $\mathrm{Ca^{2+}}$?

A white precipitate, which does not redissolve in excess sodium hydroxide solution.

What are the steps to write the ionic equation for a metal hydroxide precipitating with hydroxide ions?
e.g. copper ions, $\mathrm{Cu^{2+}}$

1. Write the metal ion with its charge: $\mathrm{Cu^{2+}}$
2. Add enough $\mathrm{OH^-}$ ions to balance the charge: $\mathrm{Cu^{2+} + 2OH^-}$
3. The product is the hydroxide precipitate: $\mathrm{Cu^{2+} + 2OH^- \rightarrow Cu(OH)_2}$

True or false? The green precipitate formed when sodium hydroxide solution is added to iron(II) ions turns brown on standing in air.

True. The iron(II) hydroxide is oxidised by air to brown iron(III) hydroxide.