Question

What will be the equivalent weight of $KCl{O_3}$ in the following reaction?
$3KCl{O_3}\; + \;3{H_2}S{O_{4\;\;}}\; \to \;\;3KHS{O_{4\;\;}} + \;HCl{O_4}\; + \;2Cl{O_2}\;\; + \;{{\text{H}}_2}{\text{O}}$

Answer 1

Hint: We are given a redox reaction so first we should learn what redox reaction is. A redox reaction is a chemical oxidation-reduction reaction in which reactant atoms undergo a change in their oxidation state. Redox is a short form of reduction-oxidation. All redox reactions can be divided into two processes: oxidation process and reduction process. We will study the change in oxidation state of each molecule to calculate the equivalent mass of a given molecule.

Complete answer:
We are calculating equivalent weight, we should know first what is equivalent weight of a molecule. Equivalent weight is the mass of one equivalent mass of a given molecule that will combine with or react with a fixed amount of another molecule.
Disproportionation reaction
Oxidation
$Cl{O_3}^{ - \;}\; \to \;Cl{O_4}^{ - \;\;}\; + \;2{{\text{e}}^ - }$
Calculating the change in oxidation state of Chlorine in above reaction, the chlorine is going $ + 5$ oxidation state to $ + 7$ oxidation state so change in oxidation state is two. Equivalent weight in this reaction
${{\text{M}}_{oxd}}\; = \dfrac{{\;{\text{M}}}}{2}$
where M is the molar mass of $KCl{O_3}$
Reduction
$\;{{\text{e}}^ - }\; + \;Cl{O_3}^{ - \;\;} \to \;Cl{O_2}$
Calculating the change in oxidation state of Chlorine in above reaction, Chlorine changes its oxidation state from $ + 5$ to $ + 4$. Equivalent weight in this case
${{\text{M}}_{red}}\; = {\text{M}}$
Total equivalent weight will be the sum of equivalent weights in oxidation and reduction
${{\text{M}}_{eq}}\; = {\text{M}}\; + \;\dfrac{{\;{\text{M}}}}{2}$
Substituting the value of Molar mass of $KCl{O_3}$ we get,
${{\text{M}}_{eq}}\; = \;183.825\;gmo{l^ - }$

Note:
Equivalent weight is also known as gram equivalent; it is calculated by dividing the molar mass of a molecule by its valence or oxidation number in our case. Chlorine is undergoing oxidation and reduction in the same reaction; this type of reaction is known as a disproportionation reaction.