Sodium extract is heated with concentrated HNO _3 before testing for halogens because :

JEE Main 2016 Chemistry question

Sodium extract is heated with concentrated before testing for halogens because :

(1) and AgCN are soluble in acidic medium.
(2)Silver halides are totally insoluble in nitric acid.
(3) and , if present, are decomposed by conc. and hence do not interfere in the test.Correct
(4)Ag reacts faster with halides in acidic medium

Answer: (3)

Solution

After Lassaigne's sodium fusion the extract may contain and as well as halide ions. If the extract were simply acidified and treated with silver nitrate, these would precipitate as black and white AgCN, which would be mistaken for a positive halogen test. Boiling

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Question ID VK-115624