Buffer Solutions

Question 1

What is a buffer solution?

Answer 1

A system that minimises pH changes when small amounts of an acid or base are added by using conjugative acid-base pairs

Question 2

Describe how to prepare a weak acid buffer solution.

Answer 2

• needs a weak acid and its conjugate base
• eg. Mix together a solution of a weak acid with a solution of one of its salts, which provides the conjugate base when dissolved into solution

Question 3

Describe how to prepare a buffer solution from the partial neutralisation of a weak acid.

Answer 3

• add an aqueous solution of an alkali to an excess of a weak acid
• the weak acid is partially neutralised by the alkali, forming the conjugate base

Question 4

How does the addition of an acid shift the position of equilibrium to restore pH?

Answer 4

1. The [ H+ ] increases
2. The H+ ions react with the conjugate base
3. The position of equilibrium shifts left to remove the H+ ions

Question 5

How does the addition of an alkali shift the position of equilibrium to restore pH?

Answer 5

1. The [ OH- ] increases
2. OH- reacts with the smaller concentration of H+ so [ H+ ] decreases
3. The position of equilibrium shifts right as the weak acid dissociates more to increase [ H+ ]

Question 6

What is the equation for calculating the pH of a buffer solution?

Answer 6

[ H+ ] = Ka x [ HA ] / [ A- ]

Question 7

What buffer system controls blood pH?

Answer 7

Carbonic acid - hydrogencarbonate buffer system

Question 8

What pH range should blood fall between?

Answer 8

7.35 -7.45

Question 9

What happens as a result of blood pH falling below 7.35?

Answer 9

• people can develop acidosis which can cause fatigue, shortness of breath, shock or death

Question 10

What can happen as a result of blood pH rising above 7.45?

Answer 10

• people can develop alkalosis, which can cause muscle spasms, light-headedness and nausea

Question 11

What is the equilibrium for the carbonic acid - hydrogencarbonate buffer system?

Answer 11

H2CO3 (aq) <—> H+ (aq) + HCO3- (aq)