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Difficulty: HardDefinitions and Theories of Acids and Bases
In liquid ammonia as a solvent, ammonium ions react with amide ions according to the following ionic equilibrium equation:
NH4++NH2−⇌2NH3NH_4^+ + NH_2^- \rightleftharpoons 2NH_3
Based on the Brønsted-Lowry theory of acids and bases, which of the following statements correctly identifies the acid and its corresponding conjugate base in the forward reaction?
  1. NH4+NH_4^+ is the acid, and NH3NH_3 is its conjugate base.Answer
  2. B
    NH4+NH_4^+ is the acid, and NH2−NH_2^- is its conjugate base.
  3. C
    NH2−NH_2^- is the acid, and NH3NH_3 is its conjugate base.
  4. D
    NH3NH_3 is the acid, and NH4+NH_4^+ is its conjugate base.

Answer

The species NH4+NH_4^+ acts as the acid, and NH3NH_3 is its corresponding conjugate base.
According to the Brønsted-Lowry concept, an acid is a proton (H+H^+) donor, and a conjugate base is the species formed when an acid loses a proton. In the given reaction, NH4+NH_4^+ donates a proton to NH2−NH_2^-, producing NH3NH_3. Therefore, NH4+NH_4^+ is the acid and NH3NH_3 is its conjugate base.

Step-by-Step Solution

1
Analyze the forward reaction and track proton transfer
In NH4++NH2−⇌2NH3NH_4^+ + NH_2^- \rightleftharpoons 2NH_3, NH4+NH_4^+ loses a proton (H+H^+) to form one molecule of NH3NH_3.
The Brønsted-Lowry definition specifies that an acid is a proton (H+H^+) donor.
2
Identify the Brønsted-Lowry acid
NH4+NH_4^+ is the proton donor, so it is the Brønsted-Lowry acid.
It donates H+H^+ to the amide ion (NH2−NH_2^-).
3
Determine the conjugate base formed from the acid
When NH4+NH_4^+ loses a proton, it becomes NH3NH_3.
A conjugate base is the species remaining after a Brønsted-Lowry acid donates a proton.

Key Concept

Brønsted-Lowry Acid-Base Theory and Conjugate Pairs
Estimated Time:1m 30s
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Topics

Definitions and Theories of Acids and Bases

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