A white powder A on heating turns yellow and evolves a gas C that turns limewater milky, as well as water vapour. The yellow residue B turns white on cooling, but will turn yellow again when heated.

B reacts with dilute sulphuric acid to give a colourless solution D. If dilute sodium hydroxide solution is added to D, a white precipitate E is produced which with excess alkali gives a colourless solution F.

With dilute ammonia solution D gives a white precipitate G; adding excess ammonia causes the mixture to become clear, giving solution H.

Identify all the substances A – H, and account as thoroughly as you can for the observations.

© JRG Beavon 1999

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