Acids&Bases

What is an acid (Brønsted–Lowry)?

A proton donor

What is a base (Brønsted–Lowry)?

A proton acceptor

What is a conjugate acid-base pair?

Two species that differ by a proton

What is a strong acid?

An acid that completely dissociates in aqueous solution

What is a weak acid?

An acid that partially dissociates in aqueous solution

What is pH equation?

pH = −log₁₀[H⁺(aq)]

What is Kw?

The ionic product of water

Expression for Kw?

Kw = [H⁺][OH⁻]

Value of Kw at 298 K?

1.0 × 10⁻¹⁴ mol² dm⁻⁶

What is meant by a neutral solution?

[H⁺] = [OH⁻]

What is Ka?

The equilibrium constant for the dissociation of an acid

Ka expression?

Ka = [H⁺][A⁻] / [HA]

What does a large Ka mean?

Stronger acid

What does a small Ka mean?

Weaker acid

What is pKa?

pKa = −log₁₀Ka

What does a smaller pKa mean?

Stronger acid

How does water act as an acid?

Donates a proton

How does water act as a base?

Accepts a proton

Does strength depend on concentration?

NO

Which substances are included in Ka?

Aqueous species only

What is a buffer solution?

A solution that resists changes in pH when small amounts of acid or alkali are added

What does an acidic buffer contain?

A weak acid and a salt of that acid

e.g)

• ethanoic acid + sodium ethanoate

What happens when H⁺ is added to a buffer?

The conjugate base reacts with H⁺ to form the weak acid

What happens when OH⁻ is added to a buffer?

The weak acid reacts with OH⁻ to form water

Why does pH change only slightly?

Because added H⁺ or OH⁻ is removed by reactions with buffer components

What does [A⁻] represent?

Concentration of conjugate base

What does it mean when pH = pKa?

[A⁻] = [HA]

What affects buffer capacity?

Concentration of the buffer components

How do you choose a suitable buffer?

Choose a weak acid with a pKa close to the desired pH

What assumption is made in buffer calculations?

Concentrations of HA and A⁻ remain approximately constant