Qualitative Analysis - Result Question 58

61. A soluble compound of a poisonous element $M$, when heated with $Zn / H _2 SO _4$ gives a colourless and extremely poisonous gaseous compound $N$, which on passing through a heated tube gives a silvery mirror of element $M$. Identify $M$ and $N$.

(1997)

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Solution:

The poisonous element $M$ may be As. On the basis of given information :

$\mathrm{AsCl}_3+6 \mathrm{H} \xrightarrow[\mathrm{H}_2 \mathrm{SO}_4]{\mathrm{Zn}} \mathrm{AsH}_3+3 \mathrm{HCl}$

$ 2 \mathrm{AsH}_3 \xrightarrow{\Delta} \underset{M}{2 \mathrm{As}}+3 \mathrm{H}_2 \uparrow$