Question

Why is Lassaigne's extract boiled with concentrated $HN{O}_3$ while testing for halogens?

• A. It decomposes $N{a}_{2}S$ and $NaCN$, if formed
• B. It helps in the precipitation of $AgCl$
• C. It increases the solubility product of $AgCl$
• D. It increases the concentration of $N{O}_3$ ions

Answer 1

The correct option is A It decomposes $N{a}_{2}S$ and $NaCN$, if formed

Lassaigne's extract is boiled with concentrated $HN{O}_3$ while testing for halogens as it decomposes any of the $N{a}_{2}S$ and $NaCN$ formed in the extract, so that nitrogen and sulphur do not interfere with Lassaigne's test for halogens ($NaCN$ gives a white precipitate and $N{a}_{2}S$ gives a black precipitate with silver nitrate).
Hence, option (a) is the correct answer.