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BMS02 > pH & Buffering > Flashcards

pH & Buffering Flashcards

1
Q

What is pH?

A

Measure of H+ concentration

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2
Q

What does acidity depend on?

A

FREE H+ concentration

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3
Q

Why is regulation of blood pH critical?

A

In contact with nearly every body cell

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4
Q

What is the range of normal blood pH?

A

7.35-7.45

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5
Q

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

A

Acidosis

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6
Q

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

A

Alkalosis

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7
Q

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

A

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)

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8
Q

What regulates the acid-base balance? (3)

A

Lungs

Kidneys

Chemical buffers

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9
Q

How do buffers prevent pH from increasing greatly?

A

Releasing H+/act as acids

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10
Q

How do buffers prevent pH from decreasing greatly?

A

Binding H+/act as bases

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11
Q

What is the difference between a strong and weak acid?

A

Strong acids fully dissociate at pH7

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

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12
Q

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

A

1.8 x 10^-14

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13
Q

What concentration is a pure water solution?

A

55.6M

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14
Q

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

A

10^-7M

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15
Q

[H+] x [OH-] = ?

A

10^-14(M^2)

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16
Q

What is the equation linking pKa and Ka?

A

pKa = -log[Ka]

17
Q

What is the pKa? (2)

A

pH at half-neutralisation (acid is half dissociated)

pH at which the acid will buffer best

18
Q

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

A

Low

19
Q

What is the Henderson-Hasselbalch equation?

A

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

20
Q

What does a buffer consist of?

A

Mixture of an acid and its conjugate base

21
Q

What is buffering?

A

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

22
Q

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

A

Carbonic acid H2CO3 —> HCO3 - + H+

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

Protein —> protein- + H+

Protein + —> protein + H+

23
Q

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

A

Carboxyl group (alpha)

24
Q

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

A

2

25
Q

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

A

9

26
Q

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

A

4

27
Q

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

A

Histidine 6

Lysine 10

Arginine 12

28
Q

At what pH does the R group of cysteine dissociate?

A

8

29
Q

At what pH does the R group of tyrosine dissociate?

A

10

30
Q

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

A

pKas are outside regular blood pH range

31
Q

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

A

Histidine as R group can lose H+

32
Q

Why can we use histidine as a physiological buffer?

A

In haemoglobin, neighbouring R groups affect the pKa of histidine’s R group

pKa is within physiological blood pH range

33
Q

What is the value of the critical pH?

A

5.5

34
Q

What is the definition of critical pH?

A

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

35
Q

What kind of molecules diffuse more easily across biological membranes?

A

Lipid-soluble

Uncharged

36
Q

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

A

Less dissociated aspirin (carboxyl group) at pH 2

Uncharged molecules diffuse into cells more easily

37
Q

What kind of compounds are local anaesthetics?

A

Weak bases

38
Q

Why is lignocaine injected with bicarbonate?

A

Bicarbonate increase pH

More unionised lignocaine

Drug enters more readily

BMS02 (10 decks)

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