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Units and Dimensions

Given a react...

Question

Given a reaction: ${C r}_{2} O_{7}^{2 -} + {F e}^{2 +} + H^{\oplus} ⟶ {C r}^{3 +} + {F e}^{3 +} + H_{2} O$
The balanced equation is $6 {F e}^{2 +} + 14 H^{\oplus} + {C r}_{2} O_{7}^{2 -} ⟶ 6 {F e}^{3 +} + 2 {C r}^{3 +} + 7 H_{2} O$ .
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Solution

The correct option is A 1
The unbalanced chemical equation is as follows:
${C r}_{2} O_{7}^{2 -} + {F e}^{2 +} + H^{\oplus} ⟶ {C r}^{3 +} + {F e}^{3 +} + H_{2} O$
First balance all atoms except H and O.
${C r}_{2} O_{7}^{2 -} + {F e}^{2 +} + H^{\oplus} ⟶ 2 {C r}^{3 +} + {F e}^{3 +} + H_{2} O$
The oxidation number of Cr changes from +6 to +3. Thus, it is reduced.
Total change in the oxidation number of 2 Cr atoms is $2 \times 3 = 6$ .
The oxidation number of Fe changes from +2 to +3. Thus, it is oxidized.
Total change in the oxidation number of Fe is 1.
To balance, total increase in the oxidation number with total decrease in the oxidation number, multiply $F e^{+ 2}$ and $F e^{+ 3}$ ions with coefficient 6.
${C r}_{2} O_{7}^{2 -} + 6 {F e}^{2 +} + H^{\oplus} ⟶ 2 {C r}^{3 +} + 6 {F e}^{3 +} + H_{2} O$
To balance the oxygen atoms, multiply water on RHS with coefficient 7.
${C r}_{2} O_{7}^{2 -} + 6 {F e}^{2 +} + H^{\oplus} ⟶ 2 {C r}^{3 +} + 6 {F e}^{3 +} + 7 H_{2} O$
To balance hydrogen ions, multiply hydrogen ions on LHS with coefficient 14 to obtain the balanced chemical equation.
Thus, the balanced equation is as follows:
$6 {F e}^{2 +} + 14 H^{\oplus} + {C r}_{2} O_{7}^{2 -} ⟶ 6 {F e}^{3 +} + 2 {C r}^{3 +} + 7 H_{2} O$

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Similar questions

Q. The cell reaction

{C r}_{2} O_{7}^{2 +} (a q) + 14 H^{+} (a q) + 6 {F e}^{2 +} (a q) \to 6 {F e}^{3 +} (a q) + 2 {C r}^{3 +} (a q) + 7 H_{2} O (l)

, is best represented by:

Write half-reactions using electrons.

{C r}_{2} O_{2}^{7 -} + 6 {F e}^{2 +} + 14 H^{+} ⟶ 2 {C r}^{3 +} + 6 {F e}^{3 +} + 7 H_{2} O

{C r}_{2} O_{7}^{2 -} + {F e}^{2 +} ⟶ {F e}^{3 +} + {C r}^{3 +}

(in acid solution)

Q. Balance the redox reaction by Half reaction method.

{F e}^{2 +} (a q) + {C r}_{2} O_{7}^{2 -} (a q) (acid medium) - ------- \to {F e}^{3 +} (a q) + {C r}^{3 +} (a q)

For given reaction:

{C r}_{2} O_{7}^{2 -} H^{+} - - \to {C r}^{3}

E q . w t o f {C r}_{2} O_{7}^{2 -}

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