JEE MAIN - Chemistry (2016 - 10th April Morning Slot - No. 8)
Sodium extract is heated with concentrated HNO3 before testing for halogens because :
Silver halides are totally insoluble in nitric acid.
Ag2S and AgCN are soluble in acidic medium.
S2ā and CNā, if present, are
decomposed by conc. HNO3 and hence do not interfere in the test.
Ag reacts faster with halides in acidic medium.
Explanation
Sodium fusion extract is heated with dilute HNO3 to decompose NaCN or Na2S (if present) to HCN and H2S gases, respectively.
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The presence of N or S interferes with the test of halogens by forming precipitate with AgNO3.
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