Question

Aqueous hypo solution on reaction with aqueous
\[AgN{O_3}\] gives:
A.Yellow ppt changing to black
B.White ppt changing to black
C.Orange ppt changing to blue
D.No ppt

Answer 1

Hint: Aqueous hypo solution is a chemical compound known as sodium thiosulphate which is pentahydrate and either white or colourless. It reacts with silver nitrate to form a white precipitate which further dissolves in excess hypo solution to produce a black precipitate of silver sulphide.

Complete step by step answer:
When aqueous silver nitrate reacts with aqueous hypo solution i.e., sodium thiosulphate, a precipitation reaction occurs which produces silver thiosulphate. It is a poorly soluble precipitate formed which is white in colour. It further reacts with water and results in formation of a black precipitate of sodium sulphide along with concentrated sulphuric acid.
 \[
  N{a_2}{S_2}{O_3} + 2AgN{O_3} \to A{g_2}{S_2}{O_3} + 2NaN{O_3} \\
  A{g_2}{S_2}{O_3} + {H_2}O \to A{g_2}S + {H_2}S{O_4} \\
 \]
Hence, the correct option is (B).

Additional information:
Sodium hyposulphite is neutral in charge but dissociates in water or polar solvents. It also decomposes at high temperature to give sodium sulphate along with sodium polysulphide. Its alkylation yields S-alkyl thiosulphates which are commonly called Bunte salts. It is used in medical treatments and in analytical chemistry.

Note:
Sodium thiosulphate is a strong reducing agent. When reacted with dilute hydrochloric acid it gives sulphur dioxide, water and sulphur as a product and it is cloudy due to yellow sulphur. It is also called hyposulphite of soda. The chemical equation for this reaction is:
 \[N{a_2}{S_2}{O_3}(aq) + 2HCl(aq) \to 2NaCl(aq) + S(s) + S{O_2}(g) + {H_2}O(l)\]