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PMP 102 Drugs & Medicines > pH, acid and bases, solubility, enzyme kinetic > Flashcards

pH, acid and bases, solubility, enzyme kinetic Flashcards

1
Q

pH

A

Measure of the acidity or basicity of aqueous or other liquid solutions

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2
Q

Strong Acid

A
  • Completely dissacosiates so completely ionised in water
    pH = -log[H+]
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3
Q

Strong base

A
  • Completely dissacosiates and ionised in water
  • Kw = [H+] [HO-] = 10^-14
  • pH = -log[H+]
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4
Q

Weak acid

A
  • Always in equalibrium
  • pH = 1/2 pKa - 1/2 log [HA]
  • Not compltely ionised by H2O same as initial concentration
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5
Q

Weak base

A
  • Always in equalibrium
  • pH = 1/2pKw +1/2 pKa + 1/2 log[B]
  • pKa of acid +pKb of conjugate base of acid = pKw
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6
Q

Henderson-Hasselbach equation

A

Measure of the degree of ionisation at given pH

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7
Q

Henderson hasselbalch

Weak acid

A
  • pH = pKa + log(A-/HA)
  • A- is ionised (base) and HA is unionised (acid)
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8
Q

Henderson-hasselbalch

Weak base

A
  • pH = pKa + log(B/BH+)
  • Non-ionised (base) is B and ionised (acid) is BH+
  • pKa of is the pH at which half is ionised
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9
Q

What is the dissociation why pKa = pH

A
  • Exactly half is dissacoiated so half is ionised
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10
Q

Acids

What happens when there is an increase in pH>pKa?

A
  • Acid becomes more ionised and loose electrons faster
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11
Q

Acids

What happens when there’s a decrease in pH<pKa?

A
  • Acid becomes less ionised and it is less likely that acid looses electron
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12
Q

Ratio of ionised to un-ionised

A
  • Shift by a factor of 10 if there is an increase of 1 unit int the pKa value
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13
Q

Base

What happens when there is an increase in pH>pKa?

A
  • Base becomes less ionised and is undissociated
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14
Q

Base

What happens when there is a decrease in pH<pKa?

A
  • Base becomes more ionised and dissacociated
  • More likely to gain an electron
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15
Q

Strong acid + Strong base

A

Neutral salt (pH 7)

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16
Q

Strong acid + Weak base

A

Acidic salt with pH < 7

17
Q

Weak acid + Strong base

A

Basic Salt with pH greater than 7

18
Q

Acid base titration

If there is 0.5 mol base and 1 mol acid what happens?

A
  • 0.5 moles of acid will react with 0.5 mols of base forming 0.5 mols of salt with 0.5 mols of acid left
19
Q

Buffer

A
  • Weak acid and it conjugate base or weak base with its conjugate acid
  • Ability to resist changes in pH on addition of small ammounts of acid and base
  • pH = pKa + log (Salt/Acid) when salt = acid
  • pH = pKa
20
Q

Buffer capacity

A
  • Number of moles per litre of stong acid or base required to produce an increase or decrease of 1 pH unit in the solution
  • pH = pKa + log (10/1)
  • pH = pKa +log (1/10)
  • Moving pH 1 unit up or down
21
Q

Dibacic

A

2 ionisable groups present in molecule

22
Q

Tribasic

A

3 ionisable groups in the molecule to release H+

23
Q

What does a decrease in pH causes amino acids to form?

A
  • Ammonium cation NH3+ formation therefore gaining H+
24
Q

What does a increase in pH causes amino acids to form?

A
  • Aminocarboxylate ion is formed CO2- loosing H+
25
Q

What happens when pH amino acids doesn’t change ?

A
  • Zwitterion formation where both NH3+ and COO- is present
26
Q

Isoelectric point pI

A
  • (pKa1+ pKa2) / 2
  • Concentration of zwitterion is maximum and cationic and anionic forms are equal
27
Q

What is the protonation if pH>pKa?

A
  • COOH will loose the hydrogen to form COO- and the NH2 will stay the same
28
Q

What is the protonation if pH<pKa?

A
  • NH2 with gain a proton to form NH3+ and COOH will stay the same
29
Q

Properties of ionised species

A
  • Low lipid solubility and they are unable to permeate through membranes and only non-ionised drugs are able to pass through membranes
30
Q

Weak acids

Calculation to identify the fraction of a dose that is ionised at any pH if pKa is known

A
  • As a fraction 1/1+10^(pKa-pH)
  • As a percentage 100/1+10^(pKa-pH)
31
Q

Base

Calculation to identify the fraction of a dose that is ionised at any pH if pKa is known

A
  • As a fraction 1/1+10^(pH-pKa)
  • As a percentage 100/1+10^(pH-pKa)
32
Q

Examples of

‘Like dissolves like’

A
  • Polar substance dissolves in polar solvent e.g. ethyl alcohol and H20 (miscible liquids)
  • Non-polar substance disolves in non polar solvent e.g. (miscible in one another as both are non-polar)
33
Q

Polar compound

A
  • Aqueous or in polar phase
  • Can be ionised drug or amino acid
34
Q

Non-polar compound

A
  • Non-ionised so is either non-aqueous or organic phase
35
Q

Partition coeffiecient P

A

P[Organic/Aqueous]

36
Q

Aqueous buffer

A
  • Represent aqueous compartments in the body such a blood plasma

PMP 102 Drugs & Medicines (56 decks)

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