Question

white ppt. of silver gives brown ppt. on boiling, but when it is heated$( > {300^ \circ })$, then a metallic black ppt. is obtained. Identify the compound of silver having white ppt:
$A)A{g_2}S{O_3} \\
  B)A{g_2}{S_2}{O_3} \\
  C)A{g_2}C{O_3} \\
  D)AgCl $

Answer 1

Hint: Silver carbonate is insoluble in water like most transition metal carbonates. Freshly prepared silver carbonate is colorless, but the solid quickly turns yellow Silver carbonate on celite is also called as Fetizon's reagent. It is obtained by precipitation of solution of silver nitrate by an alkaline carbonate that is white in color and becomes yellow when the soluble salts are washed.

Complete answer:
Silver nitrate gives a white precipitate with aqueous sodium thiosulphate the precipitate dissolves in excess of thiosulphate. If the precipitate is heated with water, it turns black, and the upper layer liquid then gives a white precipitate with acidified barium nitrate solution.
Carbonate ions also produce a white precipitate with silver nitrate solution. The acid reacts with any carbonate ions present. When a few drops of a silver nitrate solution are added to a slightly acidic aqueous solution that contains chloride ions, a white precipitate of silver chloride will form.
So, the correct answer is $C)A{g_2}C{O_3}$.

Note:
The utilization of silver carbonate is for the production of silver powder for use in microelectronics. It is decreased with formaldehyde, creating silver liberated from soluble base metals. It is additionally utilized to change over alkyl bromides into alcohols. As a base, it has been utilized in the Wittig reaction and in $C - H$ bond activation.