C12.5 Testing for negative ions
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How can you test for a carbonate?
You can add dilute acid to a carbonate - it fizzes and produces CO2 gas
What does a carbonate + an acid make?
Metal chloride + water + CO2
What type of carbonates dissolve in water?
Group 1 carbonates such as Na and K carbonate
How can you test to show whether a chloride, bromide or iodide ions are present?
Add dilute nitric acid then silver nitrate If a precipitate forms there are halide ions present
What is the purpose of adding nitric acid?
To dissolve the compound and to remove any carbonate ions As they would also form a precipitate with the silver ions and so interfere with the test?
What colour does Iodide ions produce when reacted with nitric acid and a silver nitration solution?
Gives a yellow precipitate
What colour does Bromide ions produce when reacted with nitric acid and a silver nitration solution?
Cream precipitate
What colour does Chloride ions produce when reacted with nitric acid and a silver nitration solution?
Gives a white precipitate
How can you test an unknown compound for sulfate ions?
Adding dilute hydrochloric acid follow by barium chloride solution
What is the purpose of adding HCL?
To remove carbonate ions that would form a precipitate with the barium ions
What is a positive indicator sulfate ions are present?
A white precipitate tells you sulfate ions ar e present
Why can sulfuric acid not be added?
As it contains sulfate ions