Qualitative Analysis - Result Question 37
Passage
An aqueous solution of a mixture of two inorganic salts, when treated with dilute $HCl$ , gave a precipitate $(P)$ and filtrate $(Q)$. The precipitate $(P)$ was found to dissolve in hot water. The filtrate $(Q)$ remained unchanged, when treated with $\mathrm{H}_2 \mathrm{~S}$ in a dilute mineral acid medium. However, it gave a precipitate $(R)$ with $\mathrm{H}_2 \mathrm{~S}$ in an ammoniacal medium. The precipitate $R$ gave a coloured solution $(S)$, when treated with $\mathrm{H}_2 \mathrm{O}_2$ in an aqueous $NaOH$ medium.
37. The coloured solution $S$ contains
(a) $\mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3$
(b) $\mathrm{CuSO}_4$
(c) $\mathrm{ZnSO}_4$
(d) $\mathrm{Na}_2 \mathrm{CrO}_4$
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Answer:
Correct Answer: 37. (d)
Solution:
PLAN: $\mathrm{PbCl}_2$ is soluble in hot water.
In ammoniacal medium, cations of group III and IV may be precipitated as hydroxide or sulphide and dissolved in $\mathrm{H}_2 \mathrm{O}_2$ due to oxidation.
Thus, $P$ is $\mathrm{Pb}^{2+}$, $S$ is $\mathrm{Na}_2 \mathrm{CrO}_4$.
BETA
