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20 chemistry for the biosciences > L4 - pH and buffering > Flashcards

L4 - pH and buffering Flashcards

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1
Q

what is the average blood pH

A

7.35 - 7.45

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2
Q

what is the living blood pH range

A

7.0 - 7.8

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3
Q

sources of acids?

A

diet (vinegar / lemon / chilli)
protein breakdown
incomplete oxidation of fats/carbs
CO2 transport in blood

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4
Q

what does a buffer consist of

A

weak acid and conj base

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5
Q

what regulates pH

A

lungs
kidneys
chemical buffers

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6
Q

what does a buffer do

A

resists changes in pH by
releasing H+ when pH high
binding H+ when pH drops

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7
Q

what is the M of pure water

A

55.6 Moles per litre

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8
Q

what is pKa

A

the pH at which the weak acid is half dissociated

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9
Q

what does lower pKa mean

A

stronger weak acid

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10
Q

what does higher pKa mean

A

weaker weak acid

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11
Q

why is pKa the pH at which an acid will buffer best

A

because there is plenty of acid and conj base to accept / donate H+

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12
Q

list physiologically important buffers

A
  1. H2CO3 —> HCO3-
  2. H2PO4 —> HPO4 2-
  3. protein —> protein-
  4. protein —> protein+
  5. NH4+
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13
Q

what happens when [HCO3-] low

A

metabolic acidosis

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14
Q

what happens when [H2CO3] high

A

respiratory acidosis

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15
Q

give an example of an amino acid that is a good physiological buffer and its pKa

A

histidine

pKa 6

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16
Q

why is haemoglobin a good blood buffer

A

contains many histidine residues

17
Q

which amino acids can dissociate?

A

the charged ones

18
Q

is histidines pKa 6 in Hb?

A

no, surrounding groups affect it

19
Q

what is pKa of oxy Hb

A

6.8

20
Q

what is pKa of deoxy Hb

A

7.8

21
Q

why is the pKa of deoxy Hb different?

A

removing O causes conformational change causing different surrounding groups

22
Q

what is the state of a weak acid above its pka?

A

more dissociated (more free H+)

23
Q

what is the state of a weak acid below its pKa

A

less dissociated

24
Q

is deoxy or oxy Hb a better carrier of H+ at physiological pH

A

deoxy because it is less dissociated

20 chemistry for the biosciences (7 decks)

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