14.1 Brønsted-Lowry Acids and Bases - Chemistry 2e _ OpenStax

Identify acids, bases, and conjugate acid-base pairs according to Brønsted-Lowry definition.
Write equations for acid and base ionization reactions.
Use the ion-product constant for water to calculate hydronium and hydroxide ion concentrations.
Describe the acid-base behavior of amphiprotic substances.

1680: Robert Boyle observed traits of acids, such as:
- Ability to dissolve substances.
- Changing colors of natural dyes.
- Losing traits upon contact with alkalis (bases).
18th century: Recognition of acids by:
- Sour taste.
- Reaction with limestone to release CO₂.
- Formation of neutral substances with alkalis.
1815: Humphry Davy demonstrated that hydrogen is essential in acids.
Around the same time, Joseph Louis Gay-Lussac concluded:
- Acids neutralize bases; defined in terms of each other.
1884: Svante Arrhenius defined:
- Acids yield hydronium ions in water.
- Bases yield hydroxide ions in water.
1923: Brønsted and Lowry proposed:
- Acids as proton donors and bases as proton acceptors.

Acid-base reaction involves proton transfer from an acid (donor) to a base (acceptor).
Conjugate pairs:
- Acid donates H⁺, remaining species is the conjugate base.
- Base accepts H⁺, forming conjugate acid.
- Example: Water and ammonia reaction:
  - Water donates a proton, becoming OH⁻ (conjugate base).
  - Ammonia accepts a proton, forming NH₄⁺ (conjugate acid).
Reverse reaction:
- OH⁻ accepts a proton from NH₄⁺.

Acid Ionization: Reaction between a Brønsted-Lowry acid and water.
- Example: Hydrogen fluoride (HF) ionizes in water to form hydronium ions (H₃O⁺) and fluoride ions (F⁻).
Base Ionization: Occurs when a base accepts protons from water.
- Example: Pyridine (C₅H₅N) ionizes in water, yielding hydroxide (OH⁻) and pyridinium ions (C₅H₅NH⁺).

Water can act as both an acid and a base:
- Donating protons (acid) in reactions.
- Accepting protons (base) in other reactions.
Compounds that can donate or accept protons are termed amphiprotic (or amphoteric).