Sodium extract is boiled with con. $\mathrm{HNO}_{3}$ before testing for halogens . Otherwise ,\

Question

Professor PC Thomas Classes · Answer

Sodium sulphide and cyanide will interfere in silver nitrate test for halogens, as follows. $$ \begin{aligned} \mathrm{Na}_{2} \mathrm{~S}+2 \mathrm{AgNO}_{3} ightarrow \underset{3}{\mathrm{Ag}_{2} \mathrm{~S}}+ & 2 \mathrm{NaNO}_{3} \ & 	ext { black } \ \mathrm{NaCN}+\mathrm{Ag} \mathrm{NO} & ightarrow \underset{	ext { white }}{\mathrm{AgCN}}+\mathrm{NaNO}_{3} \end{aligned} $$ Nitric acid can eliminate $\mathrm{Na}_{2} \mathrm{~S}$ and NaCN from solution as follows.\ $\mathrm{Na}_{2} \mathrm{~S}+2 \mathrm{HNO}_{3} ightarrow \mathrm{H}_{2} \mathrm{~S} \uparrow+2 \mathrm{NaNO}_{3}$\ $\mathrm{NaCN}+\mathrm{HNO}_{3} ightarrow \mathrm{HCN} \uparrow+\mathrm{NaNO}_{3}$\