Question

The number of moles of ${\text{KMn}}{{\text{O}}_4}$ that will be needed to react with one mole of sulphite ion in acidic solution is:
A.$\dfrac{2}{5}$
B.$\dfrac{3}{5}$
C.$\dfrac{4}{5}$
D.1

Answer 1

To calculate the number of moles needed we need to write the balanced chemical equation. In an acidic medium the sulphite ions get converted to sulphate ions.

Complete step by step answer:
In acidic medium potassium permanganate that is ${\text{KMn}}{{\text{O}}_4}$ acts as an oxidising agent. It is a very good oxidising agent. It oxidises the sulfite ion to sulphate ions. The reacts occurs as:
$2{\text{MnO}}_4^ - + 5{\text{SO}}_3^{2 - } + 6{{\text{H}}^ + } \to 2{\text{M}}{{\text{n}}^{2 + }} + 5{\text{SO}}_4^{2 - } + 3{{\text{H}}_2}{\text{O}}$
In the balanced chemical equation we can see that for 2 moles of potassium permanganate produces 5 moles or oxidises five moles of sulphite to sulphate ions. We can also say that 5 moles of sulfate reacts with 2 mole of potassium permanganate.
So, 1 mole of sulphite will react with $\dfrac{2}{5}$ moles of potassium permanganate.

Hence the correct option is A.

Additional information:
Potassium permanganate is purple coloured solid. It gives intense violet colour when mixed with water. It is used as an oxidising agent, in titrations, as disinfectants and dermatitis. It is also listed in the WHO list of essential medicines. It is also used to treat waste water treatment. It is used to treat skin infections such as fungal infections. Potassium permanganate as an oxidiser can cause irritation on skin when contacted directly.

Note:
The oxidation state of manganese is 7. Manganese has the atomic number 25 and has 7 electrons in its valence shell. In potassium permanganate the manganese is in its maximum oxidation state and hence cannot lose any further electrons. That is why it always acts as an oxidising agent because it can reduce itself by gaining electrons and can never lose electrons.