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When performing the tests for choride ions and sulphate ions, why is acid added?

April 26, 2017acid Chemistry choride ions Mathematics Performing Sulphate tests

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When performing the tests for choride ions and sulphate ions, why is acid added?

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In the test for chloride ions, you add silver nitrate solution to a solution of the unknown. If chloride is present you get a white ppt of silver chloride. However, if carbonate is present you get a white ppt of silver carbonate so the test is not unique to chloride. Adding nitric acid first will react with any carbonate and you will see effervescence so you can easily distinguish carbonate from chloride. In the test for sulphate ions, you add barium chloride solution to a solution of the unknown. If sulphate is present you get a white ppt of barium sulphate. However, if carbonate is present you get a white ppt of barium carbonate so the test is not unique to sulphate. Adding hydrochloric acid first will react with any carbonate and you will see effervescence so you can easily distinguish carbonate from sulphate.