Question

Which of the following is not a conjugate acid base pair?

a) HCO3-, CO3^2-

b) H3O+, H2O

c) H2PO4-, PO4^3-

d) NH3, NH2-

Answer 1

a) HCO3-, CO3^2-

HCO3- (acid).........................> H+ + CO3^2- (conjugate base)

so it is conjugate acid base pair

b) H3O+, H2O:

H3O+(acid)......................> H+ + H2O (conjugate base)

so it is conjugate acid base pair

c) H2PO4-, PO4^3-

H2PO4- (acid)...............................> H+  HPO4^2- (conjugate base)

thus

it is not conjugate acid base pair.

d) NH3, NH2-

NH3 (acid).......................> H+ +  NH2- (conjugate base)

so it is conjugate acid base pair.

thus

option c) H2PO4-, PO4^3- is the answer.