Question

When a manganous salt is fused with a mixture of $KN{O}_3$ and solid NaOH the oxidation number of Mn changes from +2 to ?

• A. 4
• B. 3
• C. 6
• D. 7

Answer 1

Answer: (C)

6

Reaction involved:

$MnO+NaOH+KN{O}_3\to N{a}_{2}Mn{O}_4+KN{O}_2+H_{2}O$

Assign the oxidation number to Mn as:

Let the oxidation number of Mn be 'x'.

Oxidation number of $Na=+1,O=-2$.

In $MnO$: $x+(-2)=0$

$x=+2$

In $N{a}_{2}Mn{O}_4$: $2\times 1+x+4\times (-2)=0$

$x+2-8=0$ or $x=+6$

thus can be written as:

$\stackrel{+2}{M}nO+NaOH+KN{O}_3\to N{a}_2\stackrel{+6}{M}n{O}_4+KN{O}_2+H_{2}O$

When a manganous salt (MnO) is fused with a mixture of $KN{O}_3$ and solid NaOH the oxidation number of Mn changes from +2 to +6.