Question detail

Which of the following pairs represents a conjugate acid-base pair?

Try the question, check the answer, then read the explanation to understand the curriculum point.

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At a glance

MCQ

Type

practice

Style

Topic

Acids and bases (A-level only)

Question

A. HCl and Cl-
B. NH3 and NH4+
C. H2O and OH-
D. H2SO4 and HSO4-

Answer

HCl and Cl-

Explanation

A conjugate acid-base pair consists of two species that differ by a proton (H+). HCl donates a proton to become Cl-, making them a conjugate pair.

Common mistake

Identifying Conjugate Pairs

Students often confuse conjugate acid-base pairs by misidentifying the acid and its conjugate base or vice versa.

To correctly identify conjugate acid-base pairs, remember that a conjugate acid is formed when a base gains a proton (H⁺), and a conjugate base is formed when an acid loses a proton. For example, in the reaction HCl + H₂O ⇌ Cl⁻ + H₃O⁺, HCl is the acid and Cl⁻ is its conjugate base, while H₂O is the base and H₃O⁺ is its conjugate acid.

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