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Reagent used in the qualitative analysis of IVth group of basic radicals is

Option: 1

\mathrm{HCl}


Option: 2

\mathrm{H}_{2} \mathrm{S} \: \text{in alkaline medium}


Option: 3

\left(\mathrm{NH}_{4}\right)_{2} \mathrm{S}


Option: 4

\mathrm{H}_{2} \mathrm{SO}_{4}


Answers (1)

best_answer

For detection of Group IV basic radicals, \mathrm{H_2S} is added in presence of \mathrm{NH_4OH}. This is done to increase the concentration of Sulphide ions in the solution as the Group IV cations have a larger value of their Solubility products.

In presence of \text{NH}_{4}\text{OH}, the dissociation of \text{H}_{2}\text{S} is increased due to acid base reaction. This provides sufficient [S^{2-}] for precipitation of Group IV cations.

\begin{aligned} &\mathrm{H}_{2} \mathrm{~S} \rightleftharpoons 2 \mathrm{H}^{+}+\mathrm{S}^{2-} \\ &\mathrm{NH}_{4} \mathrm{OH} \rightarrow \mathrm{NH}_{4}^{+}+\mathrm{OH}^{-} \\ &\mathrm{OH}^{-}+\mathrm{H}^{+} \rightarrow \mathrm{H}_{2} \mathrm{O} \end{aligned}

Hence, the correct answer is Option (2)

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seema garhwal

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