Question

The following equations are balanced atomwise and chargewise.

(i) Cr2O72– + 8H+ + 3H2O2$\longrightarrow$ 2Cr3+ + 7H2O + 3O2

(ii) Cr2O72– + 8H+ + 5H2O2$\longrightarrow$ 2Cr3+ + 9H2O + 4O2

(iii) Cr2O72– + 8H+ + 7H2O2$\longrightarrow$2Cr3+ + 11H2O + 5O2

The precise equation/equations representing the oxidation of H2O2 is/are :

• A. (i) only
• B. (ii) only
• C. (iii) only
• D. all the three

Answer 1

Answer: (A)

(i) only

Answer 2

(1)

Cr2O72– + 14H+ + 6e– $\longrightarrow$ 2Cr3+ + 7H2O

(H2O2$\longrightarrow$ O2 + 2H+ + 2e–) × 3

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Cr2O72– + 8H+ + 3H2O2$\longrightarrow$ 2Cr3+ + 7H2O + 3O2

The reaction practically occurs with this stoichiometry.