Question

An aqueous solution of a mixture of two inorganic salts, when treated with dilute HCl, gave a precipitate (P) and a filtrate (Q). The precipitate P was found to dissolve in hot water. The filtrate (Q) remained unchanged, when treated with $H_2$S in a dilute mineral acid medium. However, it gave a precipitate with $H_2$S in an ammonical medium. The precipitate R gave a coloured solution (S), when treated with $H_2{O}_2$ in an aqueous NaOH medium.

The coloured solution S contains:

• A. $F{e}_2(S{O}_4{)}_3$
  
• B. $CuS{O}_4$
  
• C. $ZnS{O}_4$
  
• D. $N{a}_{2}Cr{O}_4$

Answer 1

The correct option is D $N{a}_{2}Cr{O}_4$

$C{r}^{3+}\underset{ammonical}{\overset{H_{2}S}{\to }}Cr(OH{)}_3\underset{H_2{O}_2}{\overset{NaOH}{\to }}N{a}_{2}Cr{O}_4$