What do you observe when caustic soda solution is added to the following solution, first a little and then in excess:
(a) $F e C l_{3}$ ,

(b) $Z n S O_{4}$ ,
(c) $P b (N O_{3})_{2}$ ,

(d) $C u S O_{4}$ ?
Write balanced equations for these reactions.

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Solution

(i) $F e C I_{3} + 3 N a O H ⟶ F e (O H)_{3} ↓ 3 N a C I$

In excess of alkali, the reddish brown ppt, of $F e (O H)_{3}$ remains insoluble

(ii) $Z n S O_{4} + 2 N a O H ⟶ Z n (O H)_{2} ↓ + N a S O_{4}$

In excess of alkali, white gelatinous ppt. of $Z n (O H)_{2}$ becomes soluble

$Z n (O H)_{2} + 2 N a O H (E x c e s s) ⟶ N a_{2} Z n O_{2} + 2 H_{2} O$

(iii) $P b (N O_{3})_{2} + 2 N a O H ⟶ P b (O H)_{2} ↓ + 2 N a N O_{3}$

In excess of alkali, the white precipitate of $P b (O H)_{2}$ become soluble:

$P b (O H)_{2} + 2 N a O H (e x c e s s) ⟶ N a_{2} P b O_{2} + 2 H_{2} O$

(iv) $C u S O_{4} + 2 N a O H ⟶ C u (O H)_{2} ↓ + 2 N a S O_{4}$

In excess of alkali, the pale blue precipitate of $C u (O H)_{2}$ is insoluble

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