pH, acid and bases, solubility, enzyme kinetic

Question 1

pH

Answer 1

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

Question 2

Strong Acid

Answer 2

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

Question 3

Strong base

Answer 3

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

Question 4

Weak acid

Answer 4

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

Question 5

Weak base

Answer 5

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

Question 6

Henderson-Hasselbach equation

Answer 6

Measure of the degree of ionisation at given pH

Question 7

Henderson hasselbalch

Weak acid

Answer 7

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

Question 8

Henderson-hasselbalch

Weak base

Answer 8

• 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

Question 9

What is the dissociation why pKa = pH

Answer 9

• Exactly half is dissacoiated so half is ionised

Question 10

Acids

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

Answer 10

• Acid becomes more ionised and loose electrons faster

Question 11

Acids

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

Answer 11

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

Question 12

Ratio of ionised to un-ionised

Answer 12

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

Question 13

Base

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

Answer 13

• Base becomes less ionised and is undissociated

Question 14

Base

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

Answer 14

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

Question 15

Strong acid + Strong base

Answer 15

Neutral salt (pH 7)

Question 16

Strong acid + Weak base

Answer 16

Acidic salt with pH < 7

Question 17

Weak acid + Strong base

Answer 17

Basic Salt with pH greater than 7

Question 18

Acid base titration

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

Answer 18

• 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

Question 19

Buffer

Answer 19

• 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

Question 20

Buffer capacity

Answer 20

• 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

Question 21

Dibacic

Answer 21

2 ionisable groups present in molecule

Question 22

Tribasic

Answer 22

3 ionisable groups in the molecule to release H+

Question 23

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

Answer 23

• Ammonium cation NH3+ formation therefore gaining H+

Question 24

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

Answer 24

• Aminocarboxylate ion is formed CO2- loosing H+

Question 25

What happens when pH amino acids doesn't change ?

Answer 25

- Zwitterion formation where both NH3+ and COO- is present

Question 26

Isoelectric point pI

Answer 26

- (pKa1+ pKa2) / 2 - Concentration of zwitterion is maximum and cationic and anionic forms are equal

Question 27

What is the protonation if pH>pKa?

Answer 27

- COOH will loose the hydrogen to form COO- and the NH2 will stay the same

Question 28

What is the protonation if pH

Answer 28

- NH2 with gain a proton to form NH3+ and COOH will stay the same

Question 29

Properties of ionised species

Answer 29

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

Question 30

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

Answer 30

- As a fraction 1/1+10^(pKa-pH) - As a percentage 100/1+10^(pKa-pH)

Question 31

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

Answer 31

- As a fraction 1/1+10^(pH-pKa) - As a percentage 100/1+10^(pH-pKa)

Question 32

# Examples of 'Like dissolves like'

Answer 32

- 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)

Question 33

Polar compound

Answer 33

- Aqueous or in polar phase - Can be ionised drug or amino acid

Question 34

Non-polar compound

Answer 34

- Non-ionised so is either non-aqueous or organic phase

Question 35

Partition coeffiecient P

Answer 35

P[Organic/Aqueous]

Question 36

Aqueous buffer

Answer 36

- Represent aqueous compartments in the body such a blood plasma