5.1.12: The ionisation of water and Kw

Question 1

What is Kw?

Answer 1

The ionic product of water.

Question 2

What is the formula for Kw?

Answer 2

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

Question 3

How can water act as an acid?

Answer 3

By donating a proton:

H2O(l) → H+ (aq) + OH- (aq)

Question 4

How can water act as a base?

Answer 4

By accepting a proton:

H2O(l) + H+ (aq) → H3O+(aq)

Question 5

What is the eqm. that water exists in?

Answer 5

H2O(l) ↔ H+ (aq) + OH- (aq)

Question 6

What is the equation of Kw?

Answer 6

Kw = [H+] [OH-]

Question 7

What are the units for Kw?

Answer 7

mol2dm-6

Question 8

At 25 degrees celsius, what is the value of Kw?

Answer 8

Kw= 1.00 x 10^-14

Question 9

How do we measure the strength of bases?

Answer 9

By their ability to dissociate in solution to release OH- ions.

Question 10

How is NaOH a strong base?

Answer 10

In aqueous solution, NaOH dissociates completely.

NaOH(aq) → Na+(aq) + OH-(aq)

Question 11

What are alkalis?

Answer 11

Bases that dissociate in water to release hydroxide ions.

Question 12

How is NH3 a weak base?

Answer 12

-In aqueous solution, an equilibrium is set up.
-The equilibrium position lies well to the left-hand side:
NH3(aq) + H2O(l) ↔ NH4+(aq) + OH-(aq)

Question 13

How do you calculate the pH of a strong base?

Answer 13

1. [OH-] = [NaOH]
2. find [H+] by rearranging Kw=[H+] [OH-]
3. Find pH by using pH= -log[H+]