Question

The conjugate base of $HCO_3^ -$ is:
A) ${H_2}C{O_3}$
B) $CO_3^{2 - }$
C) $C{O_2}$
D) ${H_2}O$

Answer 1

Firstly we should be clear what exactly is the conjugate base for an acid. That we get as what we can describe as a left over after an acid has donated a proton during a chemical reaction. Now that means that if we take back a $({H^ + })$ from the acid then the left over would be the conjugate base.

Complete solution:
Firstly we should be aware that the question is regarding the combining capacity of any atom of any element with another element.
We can say that a conjugate base is what we can describe as a left over after an acid has donated a proton during a chemical reaction. Hence we get that a conjugate base is a derivative species that is formed by the removal of a proton from an acid. This can be considered as in the reverse reaction it is able to gain a hydrogen ion. Because some acids are capable of releasing multiple protons, we can say that the conjugate base of an acid could in turn itself be acidic.
Apart from that a more general definition is that a conjugate base is the base member, X-, of a pair of compounds that transform into each other by gaining or losing a proton.
Now after knowing that we know that to get the conjugate base we just have to take back a proton $({H^ + })$ .
So that would leave us with the conjugate base as $CO_3^{2 - }$ .

So, the correct answer will be option number B.

Note: Johannes Nicolaus Brønsted and Martin Lowry introduced the Brønsted–Lowry theory, which proposed that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base.