The Lassaigne's extract is boiled with conc HNO_3 while testing for halogens. By doing so it

Correct answer: (D) decomposes Na_2 ~S and NaCN , if formed. Na_2 ~S and NaCN, if present in the extract, will be decomposed to H_2 ~S and HCN by HNO_3 . NaCN+HNO_3 longrightarrow NaNO_3+HCN Na_2 ~S+2 HNO_3 longrightarrow 2 NaNO_3+H_2 ~S These will escape from the solution and will not interfere with the test for halogens.

Q62 / 200 · NEET 2011 (Screening) · Chemistry

The Lassaigne's extract is boiled with conc $\mathrm{HNO}_3$ while testing for halogens. By doing so it

A
helps in the precipitation of $\mathrm{AgCl}$
B
increases the solubility product of $\mathrm{AgCl}$
C
increases the concentration of $\mathrm{NO}_3^{-}$ions
Correct answer
D
decomposes $\mathrm{Na}_2 \mathrm{~S}$ and $\mathrm{NaCN}$, if formed

Solution

$\mathrm{Na}_2 \mathrm{~S}$ and NaCN, if present in the extract, will be decomposed to $\mathrm{H}_2 \mathrm{~S}$ and $\mathrm{HCN}$ by $\mathrm{HNO}_3$. $$ \begin{aligned} & \mathrm{NaCN}+\mathrm{HNO}_3 \longrightarrow \mathrm{NaNO}_3+\mathrm{HCN} \\ & \mathrm{Na}_2 \mathrm{~S}+2 \mathrm{HNO}_3 \longrightarrow 2 \mathrm{NaNO}_3+\mathrm{H}_2 \mathrm{~S} \end{aligned} $$ These will escape from the solution and will not interfere with the test for halogens.

Hence, the correct answer is option: 'D'.

The Lassaigne's extract is boiled with conc $\mathrm{HNO}_3$ while testing for halogens. By doing so it

Solution

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