8.3 Strong And Weak Acids And Bases

Question 1

What happens when an acid reacts with water?

Answer 1

It dissociates or ionises.

Question 2

How can the reaction of acid with water be written?

Answer 2

HA (aq) + H2O (l) H3O+ (aq) + A- (aq)

or

HA (aq) H+ (aq) + A- (aq)

It can be shown with or without water, both representations are correct.

Question 3

What is a strong acid?

Answer 3

One that dissociates completely in aqueous solution. It is a good proton donor and has a weak conjugate base.

Question 4

Where does the position of equilibrium lie for the dislocation of an acid?

Answer 4

A long way to the right, there is very little tendency for the conjugate base to pick up a proton to re form the acid.

Question 5

What is an example of a strong acid dissociating?

Answer 5

Hydrochloric acid

HCl (aq) ——> H+ (aq) + Cl- (aq)

Question 6

What is a weak acid?

Answer 6

One that dissociates partially aqueous solution.

Question 7

What is an example of a weak acid dissociating?

Answer 7

Ethanoic acid

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

Question 8

What happens the stronger the acid?

Answer 8

It dissociates more and the weaker its conjugate base.

Question 9

What is a strong base?

Answer 9

Strong bases are group 1 hydroxides and ionise completely in aqueous solution.

Question 10

What is an example of a strong base dissociating in water?

Answer 10

Sodium hydroxide

NaOH (aq) —-> Na+ (aq) + OH- (aq)

Question 11

What happens when a weak base reacts with water?

Answer 11

It accepts a proton from the water and ionises according to the equation:
B (aq) + H2O (l) BH+ (aq) + OH- (aq)

Question 12

What happens the stronger the base?

Answer 12

The stronger the base the better it is at accepting a proton and the weaker its conjugate acid.

Question 13

What are example of weak bases?

Answer 13

Ammonia NH3

Amines RNH2 R2NH R3N

Question 14

What is important when distinguishing experimentally between solution of strong and weak acids?

Answer 14

You must compare solutions of equal concentrations.

Question 15

How can you distinguish between strong acids and weak acids?

Answer 15

Strong acids conduct electricity bettie than solutions of weak acids.
Strong acids dissociate more therefore there is a higher concentration of (H+) ions in solution,
Strong acids have a lower pH than weak acids.
Strong acids react more violently with metal or carbonates - more rapid fizzing.

Question 16

How can you distinguish between strong bases and weak bases?

Answer 16

Solutions of strong bases have a higher pH and are better conductors than solutions of weak bases.