Question

The n-factor of ${\text{HCl}}$ in the equation:
${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}} + {\text{14HCl}} \to {\text{2KCl}} + {\text{2CrC}}{{\text{l}}_{\text{3}}} + {\text{3C}}{{\text{l}}_{\text{2}}} + {\text{7}}{{\text{H}}_{\text{2}}}{\text{O}}$
A.$\dfrac{2}{3}$
B.$\dfrac{{11}}{3}$
C.$\dfrac{7}{3}$
D.$\dfrac{3}{7}$

Answer 1

Hint: The n factor is also known as the valence factor and its value varies depending upon the compound being considered. For oxidizing agents and reducing agents, the n factor is equal to the number of electrons transferred by one mole of the oxidizing agent or reducing agent.

Complete step by step answer:
In the given reaction,
${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}} + {\text{14HCl}} \to {\text{2KCl}} + {\text{2CrC}}{{\text{l}}_{\text{3}}} + {\text{3C}}{{\text{l}}_{\text{2}}} + {\text{7}}{{\text{H}}_{\text{2}}}{\text{O}}$
Potassium dichromate is converted to chromium chloride.
In dichromate ion, chromium has an oxidation number of $ + 6$ , while in chromium chloride its oxidation number is $ + 3$ . As a result, we can say that three electrons are gained per mole of chromium atom.
Since in the given reaction, two moles of chromium atom are involved the number of electrons transferred will be $ = 2 \times 3 = 6$
Since the dichromate molecule gains $6$ electrons, thus, the other reactant, that is, hydrochloric acid must lose $6$ electrons.
The reaction involves $14$ moles of ${\text{HCl}}$.
Thus, we can say that $14$ moles of ${\text{HCl}}$ lose $6$electrons.
So, $1$mole of ${\text{HCl}}$ loses $\dfrac{6}{{14}}$electrons.
Thus, the n factor of ${\text{HCl}}$ is $\dfrac{3}{7}$.

The correct answer is D.
Note:
 In general, chemicals combine in definite ratios in the chemical reactions. Since chemical reactions can neither create nor destroy matter, nor transmute one element into another, thus the amount of each element must be the same throughout the entire reaction. For instance, the number of atoms of a given element X on the reactant side must be equal to the number of atoms of that element on the product side, irrespective of whether or not all of those atoms are involved in a reaction.