Question

Write the balanced redox reaction.

$C{u}^{2+}+S{O}_2\to C{u}^{+}+{SO}_4^{2-}$

• A. $2C{u}^{2+}+S{O}_2+2H_{2}O\to 2C{u}^{+}+4H^{+}+S{O}_4^{2-}$
• B. $2C{u}^{2+}+S{O}_2+4H_{2}O\to 2C{u}^{+}+5H^{+}+S{O}_4^{2-}$
• C. $4C{u}^{2+}+S{O}_2+3H_{2}O\to 2C{u}^{+}+4H^{+}+S{O}_4^{2-}$
• D. None of these

Answer 1

The correct option is A $2C{u}^{2+}+S{O}_2+2H_{2}O\to 2C{u}^{+}+4H^{+}+S{O}_4^{2-}$

The unbalanced redox equation is as follows:

$C{u}^{2+}+S{O}_2\to C{u}^{+}+S{O}_4^{2-}$

All atoms other than H and O are balanced.
The oxidation number of Cu changes from 2 to 1. The change in the oxidation number of Cu is 1.
The oxidation number of S changes from 4 to 6.. The change in the oxidation number of S is 2.

The increase in the oxidation number is balanced with a decrease in the oxidation number by multiplying $C{u}^{2+}$ and $C{u}^{+}$ with 2.

$2C{u}^{2+}+S{O}_2\to 2C{u}^{+}+S{O}_4^{2-}$

O atoms are balanced by adding 2 water molecules on LHS.

$2C{u}^{2+}+S{O}_2+2H_{2}O\to 2C{u}^{+}+S{O}_4^{2-}$

Hydrogen atoms are balanced by adding $4H^{+}$ on RHS.

$2C{u}^{2+}+S{O}_2+2H_{2}O\to 2C{u}^{+}+4H^{+}+S{O}_4^{2-}$

This is the balanced chemical equation.