Testing for chlorides (Cl^-), bromides (Br^-) and iodides (I^-)

1 mark · Easy

State why nitric acid is added before silver nitrate when testing a solution for halide ions.

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To remove other ions (such as carbonate or hydroxide) that may form precipitates with silver nitrate.

Also accept: To react with and remove other anions that could give a false positive with silver nitrate.; To remove ions that might also produce a precipitate with silver nitrate.

Common mistakes: Saying only 'to acidify the solution' with no reason; Saying 'to test for halides'

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Marking points

B1 · 1 mark · States that nitric acid is added to remove/react with other ions (e.g. carbonate or hydroxide) that would also give a precipitate with silver nitrate.

Worked solution

Nitric acid is added to remove ions like carbonate or hydroxide, which could also form a precipitate with silver nitrate and give a false result for halides.