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What you need to know
Reflections and Exam tips
Identifying Group 1 and Group 2 metals is carried out using flame tests, as they tend to have unique flames which we can associate with the elements.
Explanation of flame colour
The energy of the flame causes electrons in the metal ion to rise to higher energy levels, and as they fall back to their original level they give out specific frequencies of light.
A nichrome wire is dipped into concentrated hydrochloric acid and put onto the upper part of a blue flame. This is repeated until no colour is observed.
Sodium hydroxide tests for cations
Some metal ions form white or coloured precipitates when they react with sodium hydroxide.
Add dilute nitric acid followed by silver nitrate. Chlorides will produce a white precipitate, bromide a cream precipitate and iodide a yellow precipitate. To distinguish between white and cream, dilute ammonia is added and the white precipitate dissolves. When concentrated ammonia is added to the cream and yellow precipitate, the cream dissolves while the yellow does not.
Add hydrochoric acid and if substance fizzes and the gas produced turns limewater milky/cloudy its a carbonate.
Alternatively, substance is put in a boiling tube and heated strongly with the gas produced bubbled through limewater. Presence of carbonate - limewater turns cloudy.
Add hydrochloric acid followed by Barium Chloride and if white precipitate is produced its a sulphate.
Nitrates and Ammonium ion
Warm with aqueous sodium hydroxide if a gas is given off that turns red litmus blue and has a pungent smell AMMONIUM ions present. If no gas is produced add aluminium powder and warm and a pungent smell produced and red litmus turns blue then its a NITRATE.