Mole ConceptHard

Question

Silver metal in ore is dissolved by potassium cyanide solution in the presence of air by the reaction
           4 Ag + 8 KCN + O2 + 2H2O → 4 K[Ag (CN)2] + 4 KOH

Options

A.The amount of KCN required to dissolve 100 g of pure Ag is 120 g.
B.The amount of oxygen used in this process is 0.742 g (for 100 gm pure Ag)
C.The amount of oxygen used in this process is 7.40 g (for 100 gm pure Ag)
D.The volume of oxygen used at STP is 5.20 litres.

Solution

(A), (C) and (D) Explanation :
4 Ag + 8 KCN + O2 + 2 H2O → 4 K[Ag(CN)2] + 4 KOH
⇒    4 × 108 g of Ag reacts with 8 × 65 g of KCN
100 g of Ag reacts with
× 100 = 120
Hence, to dissolve 100 g of Ag , the amount of KCN required = 120 g
Hence, statement (A) is correct.
⇒  4 × 108 g of Ag require 32 g of O2
1 g of Ag require = 0.0740 g
⇒ 100 g of Ag require = 7.4 g
Hence, choice (C) is correct.
Hence, volume of O2 required = × 22.4 = 5.20 litre
Hence, (A), (C), (D) are correct while (B) is incorrect.

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