Question

Which of the following species is the conjugate acid of ammonia $\left( {{\text{N}}{{\text{H}}_3}} \right)$?
A.${{\text{N}}_2}$
B.${{\text{H}}_2}$
C.${\text{NH}}_2^ -$
D.${\text{NH}}_4^ +$
E.None of these

Answer 1

Conjugate acids are the chemical compounds that are formed when a base accepts protons from acids. Meanwhile the acid that loses a proton forms the conjugate base.

Complete step by step solution:
Conjugate acid- conjugate base pairs consist of two chemical compounds that differ in charge by $+ 1$ or $- 1$ value caused due to the movement of a proton.
We can understand the concept of conjugate acids and bases by using the Bronsted- Lowry concept of acids and bases. According to this concept, an acid is a substance that can donate a proton and base is the substance that can accept a proton.
The conjugate acid always has one more proton than its conjugate base. Or we can say that, to obtain a conjugate acid of a proton, we must add a proton to it and to obtain the conjugate base of the same, we must remove a proton from the compound.
We are supposed to find the conjugate acid of ammonia, $\left( {{\text{N}}{{\text{H}}_3}} \right)$
So we add a proton to it and we get, ${\text{N}}{{\text{H}}_3} + {{\text{H}}^ + } \to {\text{NH}}_4^ +$
Thus, the conjugate acid of ammonia is ammonium ion $\left( {{\text{NH}}_4^ + } \right)$.

Thus, the correct option is D.

Note:
The Bronsted- Lowry theory requires that an acid must contain transferrable hydrogen and it offers great freedom in defining what constitutes a base.
When an acid has donated its proton, the remaining portion of the molecule or ion is a base. This base is conjugate base. Similarly, when a base accepts a proton, it forms an acid. This acid is the conjugate acid. The base must have an unshared pair of electrons so as to accept a proton.