Question

When $HCO_3^ -$ acts as a Bronsted base, which of the following is formed?
A) $C{O_2}$
B) $C{O_3}$
C) $C{O_3}^{2 - }$
D) ${H_2}C{O_3}$

Answer 1

. Recall the definition of a Bronsted-Lowry base. A Bronsted-Lowry base or Bronsted base is any species that accepts a proton. So when $HCO_3^ -$ acts as a Bronsted base, it will accept a proton (${H^ + }$). Find the product after $HCO_3^ -$ accepts an ${H^ + }$.

Complete step by step answer:
English chemist Thomas Lowry and Danish chemist Johannes Bronsted independently proposed definitions for acids and bases in 1923 that focus on proton (${H^ + }$) transfer.
Bronsted-Lowry acid is any species that can donate a proton to another molecule whereas Bronsted Lowry base or simply, Bronsted base is any species that can accept a proton. Now, let us consider the given species, that is, $HCO_3^ -$. We are asked to find the compound it will form if it acts as a bronsted base.
If $HCO_3^ -$ acts as bronsted base, then by definition it will accept a proton.
Thus, $HCO_3^ - + {H^ + } \to {H_2}C{O_3}$

Hence by accepting a proton, $HCO_3^ -$ forms ${H_2}C{O_3}$.
Therefore, when $HCO_3^ -$ acts as a Bronsted base, ${H_2}C{O_3}$ is formed.
So, the correct answer is “Option D”.

Additional Information:
There are many theories which define acids and bases. According to Arrhenius theory, any species that releases a proton or ${H^ + }$ ion on dissolving in an aqueous solution is called Arrhenius acid. Arrhenius base is any species that releases hydroxide ion ($O{H^ - }$) into the solution.

Note: One should also have an idea of the conjugate acid and conjugate base of $HCO_3^ -$. The species formed after accepting a proton is known as the ‘conjugate acid’ of a Bronsted- Lowry base whereas the species formed after donating a proton is known as the’ conjugate base’ of a Bronsted-Lowry acid. Thus, ${H_2}C{O_3}$ is the conjugate acid of $HCO_3^ -$. The conjugate base of $HCO_3^ -$ will be $C{O_3}^{2 - }$.