Conjugate acid–base pairs | Chemical reactions | AP Chemistry | Khan Academy | Summary and Q&A

TL;DR

Conjugate acid-base pairs in chemistry are two species that have the same formula, except one has an extra proton that can be donated or accepted.

Key Insights

• ⚾ Conjugate acid-base pairs consist of an acid and a base that differ by the presence or absence of one proton.
• ⚾ The acid donates a proton, while the base accepts a proton in a chemical reaction.
• 😑 Examples of conjugate acid-base pairs include hydrofluoric acid and fluoride ion, water and hydronium ion, and hydrochloric acid and chloride ion.
• ⚾ The relationship between conjugate acid-base pairs can be generalized by representing the acid as HA and the base as A-.

Transcript

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Questions & Answers

Q: What is a conjugate acid-base pair?

A conjugate acid-base pair is composed of two species that are related by the presence or absence of one proton. The acid donates a proton to form the base, and the base accepts a proton to reform the acid.

Q: What is the relationship between hydrofluoric acid and fluoride ion?

Hydrofluoric acid (HF) is the acid, and fluoride ion (F-) is the base in the conjugate acid-base pair. HF loses a proton to form F-, while F- accepts a proton to reform HF.

Q: Can water act as a base in a conjugate acid-base pair?

Yes, in the example reaction presented, water acts as a base. It accepts a proton from HF to form the hydronium ion (H3O+), which is the conjugate acid.

Q: Are hydronium ion and hydroxide ion a conjugate acid-base pair?

No, hydronium ion (H3O+) and hydroxide ion (OH-) are not a conjugate acid-base pair. They differ by two protons, not one. They are related in the self-ionization of water.

Summary & Key Takeaways

• Conjugate acid-base pairs are related species in a chemical reaction that differ by the presence or absence of one proton.

• In a forward reaction, an acid donates a proton to form its conjugate base, while in the reverse reaction, the base accepts a proton to reform the acid.

• Examples of conjugate acid-base pairs include hydrofluoric acid (acid) and fluoride ion (base), water (base) and hydronium ion (acid), and hydrochloric acid (acid) and chloride ion (base).