Question

When $KMn{O_4}$ is reduced with oxalic acid in acidic solution, the oxidation number of Mn changes from:
A.7 to 4
B.6 to 4
C.7 to 2
D.4 to 2

Answer 1

Hint: $KMn{O_4}$ i.e. potassium permanganate is an inorganic chemical compound which consists of two ions i.e. permanganate ion and potassium ion. It is a dark purple odorless solid. Moreover, oxalic acid is a dicarboxylic acid with chemical formula ${C_2}{H_2}{O_4}$ .

Complete step by step answer:
Potassium permanganate is a dark purple odorless solid in its physical state. When the crystals of this compound are dissolved in water then the solution formed is purple in color. It is considered as a strong oxidizing agent and is usually prepared from minerals such as manganese oxide. Moreover, oxalic acid is the simplest dicarboxylic acid with condensed formula \[HOOC - COOH\] . It is produced by the oxidation of carbohydrates and can also be prepared in the laboratory by the oxidation of sucrose in the presence of nitric acid and a catalyst like vanadium pentoxide.
Now, oxidation number is basically the count of electrons that the atoms in a molecule can share, lose or gain while forming chemical bonds with other atoms of different elements. So, when $KMn{O_4}$ is reduced with oxalic acid in acidic solution, then the oxidation number of Mn changes from 7to2. Let’s see how this happens.
The reaction involved in this process is:
 $KMn{O_4} + {H_2}{C_2}{O_4} + {H_2}S{O_4} \to {K_2}S{O_4} + MnS{O_4} + C{O_2} + {H_2}O$
Let the oxidation number of Mn be x
Now, oxidation number of $S{O_4}^{2 - } = O = - 2$ and $K = + 1$
In $KMn{O_4}$ , $1 + x + 4 \times ( - 2) = 0$
$ \Rightarrow$ $x + 1 - 8 = 0 \Rightarrow x = 7$
In $MnS{O_4}$ , $x + ( - 2) = 0$ so, $x = 2$
Therefore, it is clear that when $KMn{O_4}$ Is reduced with oxalic acid in acidic solution, the oxidation number of Mn changes from +7 to +2

Hence, option C is correct.

Note: Potassium permanganate is used as a disinfectant to cure certain skin conditions like foot fungal infections, dermatitis etc. It is also used as an oxidizing agent in the chemical synthesis of many important compounds. Moreover, oxalic acid is used in the dyeing process, in removing rust, in bleaches, in removing food and ink stains and many more.