pH & Buffering

Question 1

What is pH?

Answer 1

Measure of H+ concentration

Question 2

What does acidity depend on?

Answer 2

FREE H+ concentration

Question 3

Why is regulation of blood pH critical?

Answer 3

In contact with nearly every body cell

Question 4

What is the range of normal blood pH?

Answer 4

7.35-7.45

Question 5

What is it called when your blood pH is too low?

Answer 5

Acidosis

Question 6

What is it called when your blood pH is too high?

Answer 6

Alkalosis

Question 7

How are most acids in the body generated? (3)

Answer 7

Breakdown of proteins (amino acids can make acids from N or S)

Incomplete oxidation of fats or glucose

Loading and transport of carbon dioxide in the blood (equilibrium with carbonic acid)

Question 8

What regulates the acid-base balance? (3)

Answer 8

Lungs

Kidneys

Chemical buffers

Question 9

How do buffers prevent pH from increasing greatly?

Answer 9

Releasing H+/act as acids

Question 10

How do buffers prevent pH from decreasing greatly?

Answer 10

Binding H+/act as bases

Question 11

What is the difference between a strong and weak acid?

Answer 11

Strong acids fully dissociate at pH7

Weak acids partially dissociate at pH7 (dissociation can be forced in different directions)

Question 12

What is the value of the equilibrium constant for the ionisation of water?

Answer 12

1.8 x 10^-14

Question 13

What concentration is a pure water solution?

Answer 13

55.6M

Question 14

At neutrality what is the hydrogen ion concentration in pure water?

Answer 14

10^-7M

Question 15

[H+] x [OH-] = ?

Answer 15

10^-14(M^2)

Question 16

What is the equation linking pKa and Ka?

Answer 16

pKa = -log[Ka]

Question 17

What is the pKa? (2)

Answer 17

pH at half-neutralisation (acid is half dissociated)

pH at which the acid will buffer best

Question 18

Will the pKa of a strong acid be high or low?

Answer 18

Low

Question 19

What is the Henderson-Hasselbalch equation?

Answer 19

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

Question 20

What does a buffer consist of?

Answer 20

Mixture of an acid and its conjugate base

Question 21

What is buffering?

Answer 21

Ability to resist a large change in pH when acid or base is added

Question 22

What are physiologically important buffers present in blood, saliva and other bodily fluids?

Answer 22

Carbonic acid H2CO3 —> HCO3 - + H+

Phosphoric acid H2PO4- —> HPO4 2- + H+

Protein —> protein- + H+

Protein + —> protein + H+

Question 23

Which is stronger in an amino acid: the carboxyl group or the amino group?

Answer 23

Carboxyl group (alpha)

Question 24

At what pH does the alpha carboxyl group of an amino acid dissociate?

Answer 24

2

Question 25

At what pH does the alpha amino group of an amino acid dissociate?

Answer 25

9

Question 26

At what pH does the R carboxyl group of acidic amino acids dissociate?

Answer 26

4

Question 27

At what pH do the R amino groups of each of the basic amino acids dissociate?

Answer 27

Histidine 6 Lysine 10 Arginine 12

Question 28

At what pH does the R group of cysteine dissociate?

Answer 28

8

Question 29

At what pH does the R group of tyrosine dissociate?

Answer 29

10

Question 30

Why are the alpha carboxyl and amino groups bad physiological buffers?

Answer 30

pKas are outside regular blood pH range

Question 31

Which amino acid is an important buffer of the blood and how does it buffer?

Answer 31

Histidine as R group can lose H+

Question 32

Why can we use histidine as a physiological buffer?

Answer 32

In haemoglobin, neighbouring R groups affect the pKa of histidine’s R group pKa is within physiological blood pH range

Question 33

What is the value of the critical pH?

Answer 33

5.5

Question 34

What is the definition of critical pH?

Answer 34

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

Question 35

What kind of molecules diffuse more easily across biological membranes?

Answer 35

Lipid-soluble Uncharged

Question 36

Why does aspirin diffuse into cells more easily at pH2 than pH7?

Answer 36

Less dissociated aspirin (carboxyl group) at pH 2 Uncharged molecules diffuse into cells more easily

Question 37

What kind of compounds are local anaesthetics?

Answer 37

Weak bases

Question 38

Why is lignocaine injected with bicarbonate?

Answer 38

Bicarbonate increase pH More unionised lignocaine Drug enters more readily