Chemistry 3.1.12 Acids and bases

Bronsted-Lowry acid definition

Proton donor

Bronsted-Lowry base definition

Proton acceptor

Amphoteric

Substance that can act as both an acid and a base. (e.g. water)

What is a hydronium ion

H+ ion - i.e. a proton

Strong acid

Fully dissociates e.g. HCl

Weak acid

Partially dissociates e.g. CH3COOH

Strength vs concentration of acid

Strength - amount of dissociation

Concentration - number of particles per dm3

Kw expression

Kw = [H+][OH-]

What happens if temperature of water is increased?

Position of equilibrium shifts to right (forwards endothermic direction); increases [H+] and [OH-]

Kw at 298K

K_w = 1 x 10^-14 mol²dm^-6

What is K_a?

The acid dissociation constant

Ka of a weak acid (ONLY)

[H+]²/[HA]

Equivalence point

The point at which there are exactly the right number of moles of acid required to just neutralise the base

At half equivalence point, what is true about Ka

Ka = [H+]

Buffer

Solution that resists changes in pH when small amounts of strong acid/strong base are added

How are acidic buffers made?

Aqueous solution of weak acid + aqueous solution of a salt of weak acid

How are basic buffers made?

 

Solution of a weak base with an aqueous solution of the salt of the weak base e.g NH₃ and NH₄Cl