Question

In an acidic medium, $KMn{O}_4$ oxidises $FeS{O}_4$ solution. Which of the following statements is correct ?

• A. 10mL of 1N $KMn{O}_4$ solution oxidises 10mL of 5N $FeS{O}_4$ solution.
• B. 10mL of 1M $KMn{O}_4$ solution oxidises 10mL of 5M $FeS{O}_4$ solution.
• C. 10mL of 1M $KMn{O}_4$ solution oxidises 10mL of 1M $FeS{O}_4$ solution.
• D. 10mL of 1N $KMn{O}_4$ solution oxidises 10mL of 0.1 M $FeS{O}_4$ solution.

Answer 1

The correct option is B 10mL of 1M $KMn{O}_4$ solution oxidises 10mL of 5M $FeS{O}_4$ solution.

$2KMn{O}_4+8H_{2}S{O}_4+10FeS{O}_4\to K_{2}S{O}_4+2MnS{O}_4+5F{e}_2(S{O}_4{)}_3+8H_{2}O$
One mole of $KMn{O}_4$ oxidises five moles of $FeS{O}_4$ i.e., 1M $KMn{O}_4$ can oxidise an equal volume of 5M $FeS{O}_4$.
Another way to look at it is with the idea of equivalents. 1 equivalent of each reactant reacts, since $KMn{O}_4$ has an n-factor of 5 ( oxidation state changed from +7 to +2) and $FeS{O}_4$ has an n-factor of 1 ( oxidation state changed from +2 to +3), the ratio of moles they would react in would be 1:5.