Question 12.25 Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
Class XI Organic Chemistry : Some Basic Principles and Techniques Page 363
Class XI Organic Chemistry : Some Basic Principles and Techniques Page 363
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If organic compound contains nitrogen and sulphur , the sodium extract on boiling with dilute HNO3 ( nitric acid) decomposes sodium cyanide or Sodium sulphide formed during fusion . NaCN + HNO3 ----> NaNO3 + HCN↑Na2S + 2HNO3 -------> 2NaNO3 + H2S↑
if cyanide and sulphide ions are not decomposed , they will react with silver nitrate and hence, will interfere with the test .
NaCN + AgNO3 -----> AgCN(white ppt) + NaNO3
Na2S + 2AgNO3 -----> Ag2S (black ppt) + 2NaNO3
That's why nitric acid is added to sodium extract before adding of silver nitrate for testing halogens .