3.03 Strong and weak acids

Question 1

What is meant by “dissociation” with acids?

Answer 1

When acids are added to aqueous solution, the ionise (split) to produce H+ and a negatively charged ion

Question 2

Give the ionic dissociation equation for HCl dissolving in water

Answer 2

HCl (g) —-> H+ (aq) + Cl- (aq)

Question 3

What determines the strength of an acid?

Answer 3

The proportion of acid particles that dissociate to produce H+ ions in solution

Question 4

Give three examples of strong acids

Answer 4

Sulfuric acid (H2SO4)

Hydrochloric acid (HCl)

Nitric acid (HNO3)

Question 5

How much do strong and weak acids dissociate?

Answer 5

Strong = Completely or almost completely

Weak = partially

Question 6

What pH do strong acids tend to have

Answer 6

pH 0-2

Question 7

Do nitric acid and sulfuric acid ionie completely or partially

Answer 7

Ionise completely

Question 8

Write the ionic equation for the dissociation of nitric acid

Answer 8

HNO3 (l) —-> H+ (aq) + NO3- (aq)

Question 9

Write the ionic equation for the dissociation of sulfuric acid

Answer 9

H2SO4 (l) —-> 2H+ (aq) + SO4 2- (aq)

Question 10

Give two examples of weak acids

Answer 10

Ethanoic acid (CH3COOH)

Carbonic acid (H2CO3)

Question 11

What pH do weak acids tend to have?

Answer 11

pH 2-6

Question 12

Is ionisation of a weak acid reversible or irreversible

Answer 12

Reversible (which sets up an equilibrium where ions are constantly being associated and dissociated at an equal rate)

Question 13

Write the ionic equation for ethanoic acid dissociation

Answer 13

CH3COOH (aq) <—–> H+ (aq) + CH3COO- (aq)

Question 14

Write the ionic equation for carbonic acid dissociation

Answer 14

H2CO3 (aq) <—-> 2H+ (aq) + CO3 2- (aq)

Question 15

How does acid strength differ for concentration?

Answer 15

Strength = what proportion of acid molecules ionise in water

Concentration = how much acid there is in 1 litre of water (i.e. total number of dissolved acid molecules, irrespective of how many are dissociated)

Question 16

How does pH change with concentration?

Answer 16

Increasing concentration will decrease pH, due to the increased concentration of H+ ions

Question 17

If pH decreases by 1, by what factor have the H+ ions changed?

Answer 17

Have increased by a factor of 10

Question 18

If pH decreases by 2, by what factor have the H+ ions changed?

Answer 18

Have increase by a factor of 10^2 (x 100)