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  4. In Lassaigne’s test for the detection of halogens, the sodium fusion extract is first boiled with concentrated nitric acid. This is

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Q. In Lassaigne’s test for the detection of halogens, the sodium fusion extract is first boiled with concentrated nitric acid. This is

NTA AbhyasNTA Abhyas 2022

Solution:

For the test of halogens, it is necessary to remove sodium cyanide and sodium sulphide from the sodium extract if N and S are present. It is possible by boiling sodium extract with cocn. $HNO_{3}$ as follows
$NaCN+HNO_{3} \rightarrow NaNO_{3}+HCN\uparrow$
$Na_{2}S+2HNO_{3} \rightarrow 2NaNO_{3}+H_{2}S\uparrow$