Question

Can we compare the acid strength of HClO4 and H2SO4 in aqueous solution? if your answer

is YES, explain your reasoning. However, if your answer is no, suggest a way how we can compare their acid strength?

Answer 1

We can not compare their acidic strength in aqueous solution but there is way to compare their acidic strength :

"HClO₄​​" is more acidic than H_{​​​​​​2} SO_{​​​​​4}"

1. In oxoacids higher the electronegativity of Central non metal, more the acidity.

Electronegativity of Cl is greater than S.

2. Higher the oxidation state of the central atom more the acidity.

Oxidation state of Cl In HClO4 is +7 and in H2SO4 oxidation state of S is +6.

3. Acidic character of an acid depends on the stability of the conjugate bases of that corresponding acid. Higher be the stability of the conjugate base, stronger be its acidic character. Conjugate base of HClO4 is clorate anion which is highly stabilised with due to strong delocalisation of the negative charge. Whereas for sulfuric acid the charge intensification over oxygen in Conjugate base is higher, hence less stable. So from this comparison it is clear that HClO4 removes proton in a faster way, hence more acidic.