AQA A Level chemistry - A2 Unit 4: Section 3.4.3 Acids and Bases - Bronsted.Lowry acid-base equilibria in aqueous solution

3.4.3 Acids and Bases - Bronsted.Lowry acid-base equilibria in aqueous solution

Students should:

know that an acid is a proton donor
know that a base is a proton acceptor
know that acid-base equilibria involve the transfer of protons

Bronsted-Lowry acids and bases

Bronsted-Lowry theory defines acids as proton (H⁺ ion) donors (and bases as proton acceptors).

For a compound to act as a Bronsted-Lowry acid, it must have a hydrogen atom in it, which it is capable or losing while remaining fairly stable. A Bronsted-Lowry base must be capable of accepting a hydrogen ion while remaining relatively stable (or reacting to form a stable compound...eg water and a salt). Some compounds (such as water) may act as both ie (H₂O OH^- or H₃O⁺)

Acid - base reactions always involve an acid-base conjugate pair...one is an acid, one is its conjugate base

Examples:
Compound	hydrochloric acid	ethanoic acid	water
Acid form	HCl	CH₃COOH	H₂O
Conjugate base	Cl^-	CH₃COO^-	OH^-

The conjugate base always has one less H atom that the acid (or the acid one more than the base). In compounds where there are many hydrogen atoms, the one which is held the weakest is generally the one which is lost, and this must be reflected when writing the formula...as in CH₃COOH

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