pH & Buffering

Question 1

What is pH?

Answer 1

A measure of hydrogen ion concentration

Question 2

What hydrogen ions does acidity not depend on?

Answer 2

Hydrogen ions not bound to anions

Question 3

What is the normal pH range of blood?

Answer 3

7.35-7.45

Question 4

Where does acid in the stomach come from?

Answer 4

Some acid enter in food.
Breakdown of proteins, incomplete oxidation of fats or glucose.
Loading and transport of carbon dioxide in blood.

Question 5

What is the acid - base balance regulated by?

Answer 5

The lungs, kidney, systems in the blood called chemical buffers

Question 6

What do buffers do when the pH rises or falls?

Answer 6

rise - released H+

fall - binding H+

Question 7

What molar solution is pure water?

Answer 7

55.6M solution

Question 8

What magnitude must the concentration of hydrogen ions and hydroxide ions equal?

Answer 8

10 to the -14

Question 9

How is pKa shown on an acid dissociation curve?

Answer 9

The straight line where buffering is occuring

Question 10

Where can a good blood buffer, buffer at?

Answer 10

pH 7

Question 11

What is a definition for Ka?

Answer 11

The pH at which the acid is half dissociated. There are equal amounts of undissociated acid and its conjugate base.

Question 12

The lower the pKa, the —- the acid?

Answer 12

Stronger

Question 13

What is the Henderson Hasselbalch equation?

Answer 13

pH = pKa + log (acid / conjugate base)

Question 14

How does pKa relate to buffering?

Answer 14

• Buffers are mixtures of acids and their conjugate bases
• Buffering is the ability of a solution to resist a change in pH when acid/alkali is added
• At the pKa, there are equal amounts of dissociated and non dissociated forms of the acid
• At the pKa, buffering is best

Question 15

At what pH does the alpha carboxyl and alpha amine group deprotonate?

Answer 15

carboxyl = pH 2
amine = pH 10

Question 16

Which amino acids are the ones with can dissociate?

Answer 16

Electrically charged ones

Question 17

What makes haemoglobin a good buffer?

Answer 17

The large number of histidine residues. When oxygen is delivered, the pKa value increases

Question 18

What is critical pH?

Answer 18

Highest pH at which there is a net loss of mineral from the teeth

Question 19

Why is the critical pH not an exact value?

Answer 19

The solubilty of enamel apatite varies with pH and teeth are buried in constantly replenished saliva which the concentration of calcium and phosphate ions varies.

Question 20

How could we get a tooth to withstand a lower pH before demineralising?

Answer 20

Increasing local concentrations of calcium and or phosphate

Question 21

What are all local anaesthetic agents? What two forms can the exist in?

Answer 21

Weak bases, unionised and ionised