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Organic Chemistry: Some Basic Principles and Techniques — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryOrganic Chemistry: Some Basic Principles and Techniques3 Marks
Question
Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
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Answer

While testing the Lassaigne's extract for the presence of halogens, it is first boiled with dilute nitric acid. This is done to decompose NaCN to HCN and $\mathrm{Na}_2 \mathrm{~S}$ to $\mathrm{H}_2 \mathrm{~S}$ and to expel these gases. That is, if any nitrogen and sulphur are present in the form of NaCN and $\mathrm{Na}_2 \mathrm{~S}$, then they are removed. The chemical equations involved in the reaction are represented as
$\mathrm{NaCN}+\mathrm{HNO}_3 \rightarrow \mathrm{NaNO}_3+\mathrm{HCN}$
$\mathrm{Na}_2 \mathrm{~S}+2 \mathrm{HNO}_3 \rightarrow 2 \mathrm{NaNO}_3+\mathrm{H}_2 \mathrm{~S}$

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