pH and ionisation

Question 1

What 5 properties does the amount of a compound that is in its ion form control?

Answer 1

Protein structure and enzyme activity
Interactions with other molecules e.g. protein binding
Stability and reactivity
Partition coefficient and absorption into body
Solubility and formulations of drugs

Question 2

Is the ionised form of a molecule usually more or less reactive?

Answer 2

More reactive

Question 3

What are the two methods to calculate the degree of ionisation when [HA] does not equal [A-]?

Answer 3

%A- = [A-]/([HA] + [A-]) x 100

%A- =1/(10^(pka-pH) + 1) x 100

Question 4

If a question is asking for ionisation, what is it asking for?

Answer 4

How much is in the ion form

Question 5

What can be said about the relative concentrations of HA and A- is pH = pKa?

Answer 5

If pH=pKa, then [HA]=50% and [A-]=50 %

Question 6

What can be said about the relative concentrations of HA and A- is pH = pKa+1?

Answer 6

If pH=pKa+1 then [HA]=10% and [A-]=90%

Question 7

What can be said about the relative concentrations of HA and A- is pH = pKa+2?

Answer 7

If pH=pKa+2 then [HA]=1% and [A-]=99 %

Question 8

If pH > pKa, is there more HA or A- in the solution?

Answer 8

More A-

Question 9

If pH < pKa, is there more HA or A- in the solution?

Answer 9

More HA

Question 10

If pH = pKa, is there more HA or A- in the solution?

Answer 10

If pH = pKa then [HA] = [A-]

Question 11

What is pKa1?

Answer 11

The loss of a carboxylic acid into a carboxylate

Question 12

What is pKa2?

Answer 12

The deprotonation of ammonia into an amine

Question 13

When will a titration have more than one equivalence point?

Answer 13

When there is more than one deprotonation

Question 14

What are the three steps for determining predominant forms?

Answer 14

Figure out what has a pKa
Assign pKa
Figure out which equilibrium is important