Question

Which of the following is Bronsted-Lowry base (proton acceptor) in aqueous solution?
(A) ${\text{HI}}$
(B) ${\text{NH}}_4^ + $
(C) ${\text{HCO}}_3^ - $
(D) ${{\text{H}}_2}{\text{S}}$
(E) ${\text{N}}{{\text{H}}_3}$

Answer 1

Hint: The substance which accepts proton or ${{\text{H}}^ + }$ ion from other compounds is called Bronsted-Lowry base. It is a proton acceptor. The photon theory of acids and bases is Bronsted-Lowry theory. There are some substances which are both Bronsted-Lowry acid and Bronsted-Lowry base. Water is an example of such a substance. These substances are said to be amphoteric.
$O{H^ - } + {H^ + } \rightleftharpoons {H_2}O$

Complete step by step answer:
To find if the substance is acid or base, count the number of hydrogens in substance before and after the reaction. Notice if hydrogens decreased or increased. If hydrogens are decreased after reaction then the substance is an acid. If hydrogens are increased after reaction then the substance is base. If a substance produces $O{H^ - }$after a reaction then it is Bronsted-Lowry base. Remember that strong acids have weak conjugate bases whereas weak acids have strong conjugate bases.
${{\text{H}}_2}{\text{S}} \rightleftharpoons {\text{H}}{{\text{S}}^ - } + {{\text{H}}^ + }$
${\text{HI}} \rightleftharpoons {{\text{H}}^ + } + {{\text{I}}^ - }$
${\text{NH}}_4^ + \rightleftharpoons {\text{N}}{{\text{H}}_3} + {{\text{H}}^ + }$
${\text{HCO}}_3^ - \rightleftharpoons {\text{CO}}_3^{2 - } + {{\text{H}}^ + }$
${\text{N}}{{\text{H}}_3} + {{\text{H}}^ + } \rightleftharpoons {\text{NH}}_4^ + $
Here, we can observe that $N{H_3}$ accepts a proton in the above reaction. We know that any substance which accepts a proton in an aqueous solution is called Bronsted-Lowry base.
Therefore, option E is correct.

Note: To solve questions related to Bronsted-Lowry base or Bronsted-Lowry acid, observe the number of hydrogens before and after the reaction. Check if the number of hydrogens increased or decreased. Based on this we can conclude if the substance is Bronsted-Lowry base or Bronsted-Lowry acid. If an acid and a base differ by one proton, they are called conjugate pairs. A Bronsted-Lowry base can be referred to as a proton acceptor.