Question

What is number of moles of electrons gained by one mole of oxidizing agent in the following reaction?

$Mn^{2+}_{(aq)} + 2ClO_{3(aq)} \longrightarrow MnO_{2(s)} + 2ClO_{2(aq)}$

• A. 4
• B. 3
• C. 2

Answer 1

Answer: (C)

2

Answer 2

1. Identify the oxidizing agent: In a redox reaction the oxidizing agent is reduced. Here, the chlorine‐containing species is converted from $\ce{ClO3}$ to $\ce{ClO2}$.

2. Assign oxidation numbers (using the neutral molecule interpretation): For a neutral molecule $\ce{ClO3}$:

$$\text{Let oxidation number of Cl be }x;\quad x + 3(-2)=0\implies x=+6.$$

For $\ce{ClO2}$:

$$x+2(-2)=0\implies x=+4.$$

3. Determine the change in oxidation state: Chlorine goes from $+6$ in $\ce{ClO3}$ to $+4$ in $\ce{ClO2}$. Thus, each chlorine atom gains

$$+6 - (+4) = 2 \text{ electrons.}$$

4. Answer the question: Hence, one mole of the oxidizing agent (i.e. one mole of $\ce{ClO3}$) gains 2 moles of electrons.