Qualitative and Quantitative AnalysishardMCQ SINGLE

When performing Lassaigne's test to identify halogens, the sodium fusion extract must first be boileQualitative and Quantitative Analysis Chemistry Question

Question

When performing Lassaigne's test to identify halogens, the sodium fusion extract must first be boiled with concentrated nitric acid ($HNO_3$) before the addition of silver nitrate ($AgNO_3$). The primary chemical rationale for this boiling step is to:

Answer: C

💡 Solution & Explanation

If the organic compound also contains nitrogen or sulphur, fusion creates $NaCN$ and $Na_2S$. These ions interfere with the halogen test by forming $AgCN$ (white ppt) and $Ag_2S$ (black ppt) with $AgNO_3$. Boiling with concentrated $HNO_3$ decomposes them, expelling $HCN$ and $H_2S$ gases before testing for halogens.

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