Question

Which of the following has the lowest Ka?a. carbonic acid b. dihydrogen phosphate c. phosphoric acid d. bicarbonate

Answer 1

Step-by-step explanation:

A compound or molecule which will have least dissociation and that is not able to given hydrogen ion easily upon dissociation will also have a low value of
`K_(a)`.

Dissociation of the given compounds or species will be as follows.

`H_(2)CO_(3) \rightleftharpoons H^(+) + HCO^(-)_(3)`

`H_(2)PO^(-)_(4) \rightleftharpoons H^(+) + HPO^(-)_(4)`

`H_(3)PO_(4) \rightleftharpoons H_(+) + H_(2)PO^(-)_(4)`

As, chemical formula of bicarbonate is
`HCO^(-)_(3)` and due to the presence of a negative charge it is difficult to lose a positively charged hydrogen ion. This is because oppositely charged ions will be bonded by strong force of attraction.

Hence, it will not easily lose a hydrogen ion due to which bicarbonate has the lowest
`K_(a)`.

Thus, we can conclude that out of the given species bicarbonate has the lowest
`K_(a)`.