Buffers - L7

Question 1

What is a buffer solution?

Answer 1

A solution is the property of a weak acid and conjugate base pair (or vice versa) designed to maintain pH

Question 2

How does a Buffer solution work?

Answer 2

Has a large amount of weak acid and external conjugate base added to maintain their concentrations

So when extenal strong acid added, the conjugate base can neutralise it

Question 3

Why is extra conjuate added?

Answer 3

Usually in the case of a weak acid, they don’t dissociate much and hence not a lot of conjugate is formed. So to maintain balance, more external conjugate base is added

Question 4

Is a buffer affected by dilution

Answer 4

Hopefully not

No it should not

Question 5

How is equilibrium maintained in a buffer solution?

Answer 5

When external H3O+ (acid) or OH- (external base) is added, usually the weak acid and its conjugate bases neutralise it and the reaction goes to completion, however to reach equilibrium, the H3O+ concentration is maintained.

Question 6

What formula should only be used for Buffer solutions?

Answer 6

pH = pKa + log[A-]/log[HA]

Need a versatile buffer cause we don’t know if more acid/base will be added so we need [A-]/[HA] ratio = 1 cause its log = 0 = ⇌ so pH = pKa

Question 7

Equation used for buffer solutions?

Answer 7

Henderson-Hasselbalch

Question 8

How is Henderson-Hasselbalch equation expressed in moles?

Answer 8

c = n/V

Therefore, pH = pKa + log[n A-]/log[n HA]

The V cancels out in mole equation –> partly why pH is not affected by dilution is because V cancels out and the concentrations remain

Question 9

How to make a buffer solution?

Answer 9

Either add salt of conjugate base to the weak acid

OR

Add 1/2NaOH (LR) to a weak acid to work 1/2 moles of the weak acid and its conjugate base (This is a complete reaction) <– in situ

Question 10

When does a completion reaction of a weak acid occur?

Answer 10

When a strong base is added