Question

Among the following oxoacids, the correct decreasing order of acid strength is:
(A) $HCl{O_4} > HCl{O_3} > HCl{O_2} > HOCl$
(B) $HCl{O_2} > HCl{O_4} > HCl{O_3} > HOCl$
(C) $HOCl > HCl{O_2} > HCl{O_3} > HCl{O_4}$
(D) $HCl{O_4} > HOCl > HCl{O_2} > HCl{O_3}$

Answer 1

Hint: To solve this question we should know what acidic nature is and the factor on which the acid strength depends upon. These two above mentioned points will help us come to a conclusion within no time.

Complete step by step answer:
A compound is said to be acidic in nature when the compound has the ability to furnish ${H^ + }$ ions when dissolved in water. The acidic strength depends upon the amount ${H^ + }$ions furnished. Here the acidic strength of the oxoacids can be accounted for with respect to an oxidation number of the central atom. Cl is the central atom.
The structures of oxoacids are:
 HOCl
\[HCl{O_2}\] \[\]
\[HCl{O_3}\]
\[HCl{O_4}\]
The oxidation number of chlorine atom in HClO is +1
The oxidation number of chlorine atom in $HCl{O_2}$ is +3
The oxidation number of chlorine atom in $HCl{O_3}$ is +5
The oxidation number of chlorine atom in $HCl{O_4}$ is +7
With the increase in oxidation number of Cl atom from +1 to +7, the tendency of Cl atom to attract the electron pair of Cl-O bond towards itself increases then, the rupture of the O-H bond becomes easier.
If the rupture of the O-H bond increases, the amount of ${H^ + }$ ions that furnishes will also increase.
So, the correct answer is “Option A”.

Note: The acidic strength of the oxoacids increases from HOCl< $HCl{O_2}$ < $HCl{O_3}$ < $HCl{O_4}$, as the oxidation number of Cl atom increases in this trend. According to our question we should write in decreasing order of acid strength, thus the correct answer will in this order $HCl{O_4} > HCl{O_3} > HCl{O_2} > HOCl$. The acid strength of oxoacids can be accounted for with respect to the Bronsted lowry concept of acid and base also.