Question
The Lassaigne's extract is boiled with dil. HNO _ 3 before testing for halogens because
BITSAT
Chemistry
General Organic Chemistry
2020
BITSAT 2020
BITSAT Chemistry Question (2020) — Solution
Options
- A. silver halides are soluble in HNO _ 3
- B. Na _ 2 ~S and NaCN are decomposed by HNO _ 3
- C. Ag _ 2 ~S is soluble in HNO _ 3
- D. AgCN is soluble in HNO _ 3
Answer
B. Na _ 2 ~S and NaCN are decomposed by HNO _ 3
Step-by-step solution
Na _ 2 ~S and NaCN , formed during fusion with metallic sodium, must be removed before adding AgNO _ 3 , otherwise black ppt. due to Na _ 2 ~S or white precipitate due to AgCN will be formed and thus white precipitate of AgCl will not be identified easily. Na _ 2 ~S +2 AgNO _ 3 2 NaNO _ 3 + Black Ag _ 2 ~S NaCN + AgNO _ 3 NaNO _ 3 + White Ag CN NaCl + AgNO _ 3 NaNO _ 3 + White Ag Cl Na _ 2 ~S +2 HNO _ 3 boil 2 NaNO _ 3 + H _ 2 ~S NaCN + HNO _ 3 boil NaNO _ 3 + HCN
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