Saliva 5 - Biochemistry of Buffers

Question 1

As an example what is the equilibrium for acetic acid?

Answer 1

CH3COOH⇌CH3COO- + H+

Question 2

If an acid has a small pKa (large Ka) what type of acid is it?

Answer 2

Large Ka means dissociated to large extent so strong acid

Question 3

If an acid has a large pKa (small Ka) what type of acid is it?

Answer 3

Small Ka means dissociated to small extent so weak acid

Question 4

Rearrange the equilibrium constant to the Henderson-Hesselbalch equation.

Answer 4

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

Question 5

What happens to the H-H equation if [conjugate base] = [weak acid]?

Answer 5

pH = pKA

Question 6

Define the term buffer. What does it usually consist of?

Answer 6

Buffers are molecules that resists a change in pH when small amounts of acid/ base are added.
Buffers are usually a mixture of weak acids and their conjugate base/ or weak bases with conjugate acid

Question 7

If a buffer has more weak acid within it what is better at buffering?

Answer 7

Base

Question 8

What does the pH of a buffer depend on? (HINT: H-H equation)

Answer 8

The ratio of acid component to the conjugate base component dissociation characteristics of the buffer.

Question 9

What 2 molecules is intracellular pH buffered by in the body?

Answer 9

phosphate and histidine side chains of proteins

Question 10

What molecule buffers extracellular pH?

Answer 10

Carbonic acid/ Bicarbonate ion system

Question 11

What happens to the above equilibrium if acid is added and what happens if alkali is added? (HINT: Lechateliers principle)

Answer 11

If acid is added equilibrium shifts left as to decrease the increase in h+ ions.
if base is added equilibrium shifts to the right as h+ reacts with oh- to form water to prevent drop in ph