Conjugate acid-base pair

Welcome to the seventh episode of our course on Acids and Bases. Building on our understanding of acid strength and neutralization, we now explore the dynamic relationship between acids and bases in reversible reactions. This episode introduces the concept of the 'conjugate acid-base pair.' You will learn what happens to an acid after it donates a proton and to a base after it accepts one. We will uncover the inverse relationship between the strength of an acid and its conjugate base, a critical principle in chemistry. This fundamental idea provides the theoretical groundwork for understanding buffer solutions, which we will explore later in the course.

Check your understanding

These are the same multiple-choice questions you will see in the Quiz section after you listen to the episode. Use them here to preview or review the answers.

What is the definition of a conjugate base?

  1. A substance that is formed when a base accepts a proton.
  2. A substance that remains after an acid has donated a proton.
  3. Any substance that can act as a base.
  4. The acid that is formed when a salt dissolves in water.

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

  1. HCl and Cl⁻
  2. H₂SO₄ and SO₄²⁻
  3. NH₃ and NH₄⁺
  4. H₂O and OH⁻

Hydrofluoric acid (HF) is a weak acid, while hydrochloric acid (HCl) is a strong acid. What can be concluded about their conjugate bases, F⁻ and Cl⁻?

  1. F⁻ is a stronger base than Cl⁻.
  2. Cl⁻ is a stronger base than F⁻.
  3. Both F⁻ and Cl⁻ are strong bases.
  4. The strength of the conjugate base is unrelated to the strength of the acid.
  5. Cl⁻ is a very weak base, while F⁻ is a notable weak base.

Water (H₂O) is amphoteric, meaning it can act as either an acid or a base. What is the conjugate acid of water?

  1. OH⁻ (Hydroxide ion)
  2. H₃O⁺ (Hydronium ion)
  3. O²⁻ (Oxide ion)
  4. H₂ (Hydrogen gas)

What is the conjugate base of the bicarbonate ion, HCO₃⁻?

  1. H₂CO₃ (Carbonic acid)
  2. CO₃²⁻ (Carbonate ion)
  3. CO₂ (Carbon dioxide)
  4. H₂O (Water)

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