Explain whether the halide ions act as oxidising or reducing agents in redox reactions.

Halide ions act as reducing agents in redox reactions because they lose electrons and are themselves oxidised.

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What are the colours of silver chloride, silver bromide and silver iodide precipitates?

Silver chloride is white.

Silver bromide is cream.

Silver iodide is yellow.

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What is the ionic equation, including state symbols, for the reaction between aqueous chloride ions and aqueous silver ions?

Cl-(aq) + Ag+(aq) ➔ AgCl(s)

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In the halide ion test, why is the silver nitrate solution acidified before use?

To remove any ions such as CO32- or OH- that would interfere with the test as white precipitates of silver carbonate or silver hydroxide might form which would give a false-positive result.

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What happens when aqueous Ag+ ions and dilute NH3 solution are added sequentially to a a solution of chloride ions?

Addition of Ag+: White precipitate of silver chloride forms. 

Addition of NH3: Precipitate redissolves to form a colourless solution.

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What happens when aqueous Ag+ ions and concentrated NH3 solution are added sequentially to a solution of iodide ions?

Addition of Ag+: Yellow precipitate of silver iodide forms.

Addition of NH3: No further change.

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What happens when dilute NH3 solution and concentrated NH3 solution are added sequentially to a suspension of silver bromide?

Addition of dilute NH3: No change.

Addition of concentrated NH3: Cream precipitate redissolves to form a colourless solution.

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Why is the sample acidified with dilute nitric acid before adding aqueous Ba2+ ions in the test for sulfate ions?


Acidifying the sample removes carbonate ions as carbon dioxide, preventing them from reacting with barium ions and ensuring that any white precipitate formed is specifically due to the presence of sulfate ions.

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