Question

The stoichiometry of the following reaction is:
${{\text{K}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{8}}}{\text{(aq) + 2KI(aq) }} \to {\text{2}}{{\text{K}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{(aq) + }}{{\text{I}}_{\text{2}}}{\text{(aq)}}$
A) 2:1
B) 1:2
C) 2:2
D) 1:3

Answer 1

Hint: Stoichiometry is a measure of elements. It is based on the law of conservation of mass. The concept of stoichiometry is used to determine the amount of product or reactant, using a mole ratio of a balanced chemical reaction.

Complete step by step answer:
The chemical reaction given to us is:
${{\text{K}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{8}}}{\text{(aq) + 2KI(aq) }} \to {\text{2}}{{\text{K}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{(aq) + }}{{\text{I}}_{\text{2}}}{\text{(aq)}}$
Here,
${{\text{K}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{8}}}$ = Potassium persulphate
${\text{KI}}$ = Potassium iodide
${{\text{K}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$= Potassium sulphate
${{\text{I}}_{\text{2}}}$ = Iodine
Thus, we can say that potassium persulfate reacts with potassium iodide and gives potassium sulphate and iodine. All the species are in an aqueous medium.
Now, using the balanced reaction we can determine the stoichiometry of the reaction as follows:
The coefficients of reactants in a balanced chemical reaction give us information about the number of moles of each reactant taking part in the reaction.
In the given reaction, coefficient of ${{\text{K}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{8}}}$ is 1 and the coefficient of ${\text{KI}}$ is 2 that indicates that 1 mole of ${{\text{K}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{8}}}$ react with 2 moles of ${\text{KI}}$.
So, the stoichiometric ratio of the
reactants ${{\text{K}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{8}}}$:${\text{KI}}$ is 1:2.

Thus, the correct option is (B) 1:2.

Note: Stoichiometry of the reaction is determined using the reaction coefficients of the reactant. When 1 mole of any reactant is taking part in the reaction we do not mention the coefficient. So the species with no coefficient indicates that 1 mole of that species is taking part in the reaction. Stoichiometry of the reaction helps us to determine the number of reactants reacting and the amount of product is forming.