Chemistry C3 4.2 Tests for negative ions.

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How do we identify carbonates?
By adding dilute acid, which produces carbon dioxide gas. The gas turns limewater cloudy.
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How do we identify halides?
By adding nitric acid, then silver nitrate solution. This produces a precipitate of silver halide (chloride=white, bromide=cream and iodide=pale yellow).
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How do we identify sulfates?
By adding hydrochloric acid, then barium chloride solution. This produces a white precipitate of barium sulfate.
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What is the test for carbonate ions?
Add dilute hydrochloric acid to the substance to see if it fizzes. If it does and the gas produced turns limewater milky, the substance contains carbonate ions.
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What is the test for halide ions?
Add dilute nitric acid and then silver nitrate solution. Colour of precipitate depends on the halide ions present; chloride ions=white, bromide ions=cream and iodide ions= yellow.
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What is the test for sulphate ions?
Add dilute hydrochloric acid and then barium chloride solution, if a white precipitate forms, sulfate ions are present.
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Why must you add nitric acid and not hydrochloric acid or sulphuric acid when testing with silver nitrate solution for halides?
Hydrochloric acid contains chloride ions (Cl^-) and sulphuric acid contains sulfate ions (SO_4^2-) which both give precipitate with silver nitrate solution.
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** YOU NEED TO BE ABLE TO WRITE BALANCED SYMBOL EQUATIONS FOR THE REACTIONS IN THESE TESTS - LOOK THEM UP!!!
*** YOU NEED TO LEAREN THESE TESTS AS THEY ARE IMPORTANT!!
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Card 2

Front

How do we identify halides?

Back

By adding nitric acid, then silver nitrate solution. This produces a precipitate of silver halide (chloride=white, bromide=cream and iodide=pale yellow).

Card 3

Front

How do we identify sulfates?

Back

Preview of the front of card 3

Card 4

Front

What is the test for carbonate ions?

Back

Preview of the front of card 4

Card 5

Front

What is the test for halide ions?

Back

Preview of the front of card 5
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