Acids, Buffers and Bases

Question 1

What is an acid?

Answer 1

A molecule or ion which tends to give up protons in solution

Question 2

What is a base?

Answer 2

A molecule or ion which tens to acquire protons in solution

Question 3

What is the dissociation constant?

Answer 3

Ka = [H+].[X-]/[HX]

• the stronger the acid the more the reaction is pushed to the right so greater hydrogen ion concentration and larger dissociation constant

Question 4

What is a conjugate acid?

Answer 4

When a base accepts a proton

Question 5

What is a conjugate base?

Answer 5

When an acid donates a proton

Question 6

Why is carbonic acid an important acid in biology?

Answer 6

It is formed when CO2 dissolves in blood tissue fluids. Acts as a buffer at a physiological pH

Question 7

Why is lactic acid an important acid in biology?

Answer 7

It is formed by human cells from glucose during anaerobic respiration, especially in muscle during rapid movement. Causes cramp. Is converted to glucose by gluconeogenesis in the liver

Question 8

Why is HCL an important acid in biology?

Answer 8

Secreted into the stomach as part of the digestive process

Question 9

Name a few acids produced by oral bacteria?

Answer 9

• Lactic acid
• Formic acid
• Acetic acid
• These acids are produced by different oral bacteria under anaerobic conditions
• They cause TOOTH DECAY

Question 10

Describe the process of dissolution of calcium phosphate by acids?

Answer 10

• An increase in [H+] causes the equilibrium to shift to the right, increasing the solubilisation of calcium phosphate
• An increase in calcium or phosphate concentration causes the equilibrium to shift to the left, inhibiting solubilisation and promoting re-mineralisation
• Saliva contains calcium and phosphate to aid remineralisation
• Calcium-containing foods such as milk help to protect teeth from decay

Question 11

Name for healthy plaque?

Answer 11

Open plaque

Question 12

Name for unhealthy plaque?

Answer 12

Closed plaque

Question 13

How is tooth erosion caused?

Answer 13

By the DIRECT effect of acids in the diet on the teeth

Question 14

What is a chelating agent?

Answer 14

Agents which bind strongly to divalent and trivalent cations - these bind to calcium ions, which are then no longer available to counteract calcium solubilisation

Question 15

How can you make a buffer with similar concentrations of conjugate acid and conjugate base?

Answer 15

• Neutralising an acid with OH-

- Mixing together a solution of a weak acid and one of its salts

Question 16

What equation is used to calculate the pH of a mixture of the acid and one of its salts?

Answer 16

pH = pKa + log10[salt]/[acid]

- known as the Henderson-Hasselbalch equation

Question 17

When do buffers have their greatest buffering capacity?

Answer 17

When they are 50% dissociated (pKa=pH)

Question 18

What is the main buffer in saliva?

Answer 18

Bicarbonate

Question 19

Where does the bicarbonate in saliva come from?

Answer 19

Partly from the blood and partly from the action of carbonic anhydrase

Question 20

What 3 pH ranges does phosphate act as a buffer?

Answer 20

• 2.16
• 7.21
• 12.32