Question

On adding dilute ammonia solution to a colourless solution of a salt, a white gelatinous precipitate appears. This precipitate however dissolves on addition of excess of ammonia solution.

1. From the following list, identify which metal salt solution is used above?
   Na, Al, Zn, Pb, Fe
2. What is the formula of the white gelatinous precipitate obtained?
3. Give the balanced equation(s) when sulphate of this metal reacts with ammonia solution in excess.

Answer 1

1. Zinc (Zn) metal salt solution was used
2. Zn(OH)₂
3. The balanced equations are given below:
   \[\ce{\underset{Colourless solution}{ZnSO4} + 2NH4OH -> \underset{White gelatinous ppt}{Zn(OH)2\downarrow} + \underset{Colourless in solution}{(NH4)2SO4}}\]
   With excess of NH₄OH ppt. dissolves:
   \[\ce{Zn(OH)2 + (NH4)2SO4 + 2NH4OH -> \underset{zinc (II) sulphate}{\underset{Tetrammine}{[(Zn(NH3)4)]SO4}} + 4H2O}\]