Which of the following pairs of compounds are precipitated in different group in the systematic analysis of…

Which of the following pairs of compounds are precipitated in different group in the systematic analysis of cations?
  1. $\mathrm{Bi}^{3+}, \mathrm{As}^{3+}$
  2. $\mathrm{As}^{3+}, \mathrm{Sn}^{2+}$
  3. $\mathrm{Cu}^{2+}, \mathrm{Zn}^{2+}$
  4. $\mathrm{Ba}^{2+}, \mathrm{Sr}^{2+}$

Solution

$\mathrm{Cu}^{2+}$ gives precipitate in group $\mathrm{II}$ duing qualitative analysis while $\mathrm{Zn}^{2+}$ gives precipitate in group $\mathrm{III}$
for $\mathrm{Cu}^{2+}, \quad \mathrm{Cu}^{2+}+\mathrm{H}_{2} \mathrm{S}\longrightarrow$ $\mathrm{CuS} \downarrow (black) +2 \mathrm{H}^{+}$
for $\mathrm{Zn}^{2+}, \quad \mathrm{Zn}^{2+}+\mathrm{H}_{2} \mathrm{S}\longrightarrow$ $\mathrm{ZnS} \downarrow (white) +2 \mathrm{H}^{+}$ ~

Asked in: JEE-TOPICTESTS-CHEMISTRY

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