NCERT Class XII Chemistry
Chapter - The d- and f-Block Elements
Questions with Solutions
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Question : 16
Total: 49
Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron (ii) ions (ii) S O 2
Solution:
Potassium permanganate ( K M n O 4 ) ( M n O 2 )
2 M n O 2 + 4 K O H + O 2 → 2 K 2 M n O 4 + 2 H 2 O
Electrolytically :
3 M n O 4 2 – + 4 H + → 2 M n O 4 – + M n O 2 + 2 H 2 O
M n O 4 – + 8 H + + 5 e – → M n 2 + + 4 H 2 O ( F e 2 + ) ( F e 3 + )
M n O 4 – + 8 H + + 5 e – → M n 2 + + 4 H 2 O
5 F e 2 + → 5 F e 3 + + 5 e –
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
M n O 4 – + 5 F e 2 + + 8 H + → M n 2 + + 5 F e 3 + + 4 H 2 O
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – ( S O 2 )
M n O 4 – + 8 H + + 5 e – → M n 2 + + 4 H 2 O ] × 2
10 H 2 O + 5 S O 2 → 5 S O 4 2 – + 20 H + + 10 e –
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
2 M n O 4 – + 5 S O 2 + 2 H 2 O → 5 S O 4 2 – + 2 M n 2 + + 4 H +
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
(iii)Oxalic acid
M n O 4 – + 8 H + + 5 e – → M n 2 + + 4 H 2 O ] × 2
10 H 2 O + 5 S O 2 → 5 S O 4 2 – + 20 H + + 10 e –
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
2 M n O 4 – + 5 S O 2 + 2 H 2 O → 5 S O 4 2 – + 2 M n 2 + + 4 H +
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
Electrolytically :
(iii)Oxalic acid
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