Consider the reaction below. NH4+ + H2O mc013-1.jpg NH3 + H3O+ Which is an acid-conjugate base pair? NH4+ and NH3 NH4+ and H3O+ H2O and NH3 H2O and H3O+
The Correct Answer and Explanation is :
In the given reaction:
[ \text{NH}_4^+ + \text{H}_2\text{O} \rightleftharpoons \text{NH}_3 + \text{H}_3\text{O}^+ ]
the correct acid-conjugate base pair is NH₄⁺ and NH₃.
Explanation
Acid-Base Definitions: According to the Brønsted-Lowry theory, an acid is a substance that donates a proton (H⁺), while a base is a substance that accepts a proton. An acid-conjugate base pair consists of two species that differ by a single proton.
In this reaction, NH₄⁺ (ammonium ion) acts as the acid because it donates a proton to H₂O (water). When NH₄⁺ donates a proton, it transforms into NH₃ (ammonia), which is its conjugate base. Therefore, NH₄⁺ and NH₃ are an acid-conjugate base pair.
To clarify:
- NH₄⁺ (acid) donates a proton:
[
\text{NH}_4^+ \rightarrow \text{NH}_3 + \text{H}^+
] - NH₃ (conjugate base) is what remains after the donation of the proton.
Other Options
- NH₄⁺ and H₃O⁺: This pair does not fit the acid-conjugate base definition, as H₃O⁺ (hydronium ion) does not serve as the conjugate base of NH₄⁺.
- H₂O and NH₃: Here, H₂O is a neutral molecule and NH₃ is a base. They are not an acid-conjugate base pair since they do not differ by a proton.
- H₂O and H₃O⁺: This pair includes water and hydronium ion. Although water can act as a base, H₃O⁺ is not the conjugate base of H₂O but rather the product of its protonation.
Conclusion
Thus, the correct acid-conjugate base pair from the reaction is NH₄⁺ and NH₃, as they illustrate the concept of acid-base pairs by differing by a single proton.