A.Write balanced chemical equation for each of the following.
(i) Action of hot and concentrated nitric acid on copper.
(ii) Action of hydrochloric acid on sodium bicarbonate.
(iii) Action of dilute sulphuric acid on sodium sulphide.

B. What do you observe when :
(i) Blue vitriol is heated ?
(ii) fused calcium chloride is used in the preparation of $F e C l_{3}$ ?

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Solution

A. (i) $C u (s) + 4 H N O_{3} (a q) \to C u (N O_{3})_{2} (a q) + 2 H_{2} O (l) + 2 N O_{2} (↑)$
(ii) $N a H C O_{3} (s) + H C l (a q) \to N a C l (a q) + H_{2} O (l) + C O_{2} (↑)$
(iii) $N a_{2} S (s) + H_{2} S O_{4} (a q) \to N a_{2} S O_{4} (a q) + H_{2} S (g)$

(B) (i) Blue vitriol is blue in color because it includes 5 molecules of water of crystallization $(C u S O_{4} \cdot 5 H_{2} O)$ .When heated, it loses the water of crystallization and transforms into anhydrous $C u S O_{4}$ that is grey-white in color. Thus, there is a change in color from blue to white.
$C u S O_{4} \cdot 5 H_{2} O h e a t ⟶ C u S O_{4} + 5 H_{2} O$
(Blue in color) (Grey-white in color)

(ii) As iron chloride is highly deliquescent in nature, so to keep it dry fused calcium chloride is used.

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