Chapter 21

Question 1

What is a buffer?

Answer 1

A system that minimises pH changes when small amounts of an acid or alkali are added

Question 2

What two components are in equilibrium in a buffer?

Answer 2

A weak acid
The conjugate base

Question 3

What happens in a buffer solution when an acid is added?

Answer 3

H+ ions are added to the buffer system
Initially the [H+] will increase
The large reservoir of A- ions will react with the excess H+ ions
The equilibrium position will move to the left
[H+] and pH are restored

Question 4

What happens to the buffer system when an alkali is added?

Answer 4

OH- ions are added to the buffer solution
OH- ions will react with the H+ ions
[H+] will decrease
The reservoir of HA molecules will dissociate
The equilibrium position will move to the right
[H+] and pH are restored

Question 5

How can you prepare a buffer solution?

Answer 5

Mix a solution containing the weak acid with a solution that contains a salt of the weak acid
Perform a partial neutralisation reaction

Question 6

How do you calculate the [H+] of a buffer solution?

Answer 6

Ka x ([HA]/[A-])

Question 7

How do you control the pH of the blood plasma?

Answer 7

By using the carbonic acid - hydrogen carbonate buffer solution

Question 8

What is a pH meter?

Answer 8

An electrode that is placed into the solution to measure the pH

Question 9

What is the purpose of a titration reaction?

Answer 9

To find the equivalence point for the reaction

Question 10

What is the equivalence point?

Answer 10

The volume of one solution that exactly reacts with the volume of the other solution

Question 11

What determines the equivalence point?

Answer 11

The stoichiometry
The concentrations used

Question 12

What does using an acid-base indicator allow us to do?

Answer 12

Find the equivalence point without plotting a titration curve

Question 13

Where should the indicator have a colour change?

Answer 13

In the vertical section of the titration curve
At the equivalence point
The end point and the equivalence point should coincide