Question

Four species are listed below :
(i) HCO₃^– (ii) H₃O⁺
(iii) HSO₄^– (iv) HSO₃F
Which one of the following is the correct sequence of their acid strength?
(a) iii < i < iv < ii
(b) iv < ii < iii < i
(c) ii < iii < i < iv
(d) i < iii < ii < iv

Answer 1

(d) : HSO₃ F is the super acid. Its acidic strength is greater than any given species. The pK_a value of other species are given below :
HCO₃^– →10.25
H₃ O + → –1.74
HSO₄^– → 1.92
Lesser the pK_a value, higher will be its acidic strength. Hence sequence of acidic strength will be
HSO₃F > H₃O⁺ > HSO₄^– > HCO₃^–