Ionisation of water, Kw

Question 1

Does pure water ionise?

Answer 1

Pure water ionises into H*(aq) and OH-(aq) but the extent of ionisation is tiny.

Question 2

Define Kw

Answer 2

The ionic product of water, Kw, is defined as

Kw = [H*(aq)][OH-(aq)]

At 25*, Kw = 1 x 10^-14 mol^2dm^-6

Question 3

What is the significance of Kw?

Answer 3

Kw controls the balance between [H*(aq)] and [OH-(aq)] in all aqueous solutions.

The relative concentrations of H*(aq) and OH-(aq) ions in solution are determined by Kw.

Question 4

Give the names for three strong bases.

Answer 4

Sodium hydroxide (NaOH)

Potassium hydroxide (KOH)

Calcium hydroxide (COH)

Question 5

What is an alkali?(in terms of bases)

Answer 5

Bases that dissociate in water to release hydroxide ions are called alkalis.