Question

The Lassaigne’s extract is boiled with conc. $HN{O}_3$ before testing for halogens because:

• A. $AgCN$ is soluble in $HN{O}_3$
• B. Silver halides are soluble in $HN{O}_3$
• C. $NaCN$ and $N{a}_{2}S$ are decomposed by $HN{O}_3$
• D. $A{g}_{2}S$ is soluble in $HN{O}_3$

Answer 1

The correct option is C $NaCN$ and $N{a}_{2}S$ are decomposed by $HN{O}_3$

The Lassaigne’s extract is boiled with conc. $HN{O}_3$ before testing for halogens because the cyanide and sulphide ions present in the extract will interfere in the detection of halogens.
These ions should be removed by boiling the sodium fusion extract with concentrated nitric acid which will decompose the cyanide or sulphide.