Question
An unknown inorganic compound $$(X)$$ loses its water of crystallization on heating and its aqueous solution gives the following reactions :
(i) It gives a white turbidity with dilute $$HCl$$ solution
(ii) It decolourises a solution of iodine in potassium iodide
(iii) It gives a white precipitate with silver nitrate solution which turns black on standing.
Identify the compound $$(X)$$
A.
$$N{a_2}C{O_3}.10{H_2}O$$
B.
$$N{a_2}{S_2}{O_3}.5{H_2}O$$
C.
$$N{a_2}S{O_4}.10{H_2}O$$
D.
$${\text{None of these}}$$
Answer :
$$N{a_2}{S_2}{O_3}.5{H_2}O$$
Solution :
$$\eqalign{
& X = N{a_2}{S_2}{O_3}.5{H_2}O \cr
& N{a_2}{S_2}{O_3} + 2HCl \to 2NaCl + {H_2}O + S + S{O_2} \cr
& K{I_3} + 2N{a_2}{S_2}{O_3} \to KI + 2NaI + N{a_2}{S_4}{O_6} \cr
& 2AgN{O_3} + N{a_2}{S_2}{O_3} \to A{g_2}{S_2}{O_3} + 2NaN{O_3} \cr
& A{g_2}{S_2}{O_3} + {H_2}O \to A{g_2}S + {H_2}S{O_4} \cr} $$