Lecture 8 - Acid-Base theory, pH, pKa and pKb 1

Question 1

Give three examples of drugs that are weak organic acids

Answer 1

Aspirin, ibuprofen, diclofenac.

Question 2

Give three examples of drugs that are weak organic bases

Answer 2

morphine, procaine, chloramphenicol

Question 3

Salts that are drugs

Answer 3

Sodium ibuprofen

Question 4

Why is the extent of ionisation of a drug important?

Answer 4

It has an effect on its absorption, distribution and elimination.

Question 5

What is a bronsted lowry acid?

Answer 5

proton donor

Question 6

What is a bronsted lowry base?

Answer 6

proton acceptor

Question 7

Strong acids/bases fully….

Answer 7

ionise

Question 8

Give the equation for the complete dissociation of HCl.

Answer 8

HCl –> Cl- + H+

Question 9

Weak acids/bases partially ……..

Answer 9

ions

Question 10

Weak acids only…

Answer 10

partially dissociate.

Question 11

Give the equation of the partial dissociation of the weak acid ethanoic acid

Answer 11

Question 12

Water can act as both a weak acid or base. What is the name we give for species which act as both an acid and a base?

Answer 12

ampholyte/amphiprotic solvent

Question 13

Give the equation for water as a Bronsted lowry base…

Answer 13

Question 14

What is a conjugate acid-base pair?

Answer 14

Species which are interchangeable by the movement of a single proton

Question 15

Give the equation for the dissociation of ethanoic acid in water and label the conjugate acid-base pairs.

Answer 15

Question 16

In conjugated acid base pairs, are the acid and base strong or weak?

Answer 16

weak

Question 17

In an aqueous solution, how do we represent the dissociation of a weak acid?

Answer 17

HA+H2O ⇌ A^- +H3O^+
- HA= acid 1, A^- = base 1
- H2O = Base 2, H3O^+ = acid 2

Question 18

The dissociation of a weak base can be represented in two ways…

Answer 18

Question 19

Give the simplified equation for the dissociation of a weak acid. Why is the water removed?

Answer 19

Question 20

The equilibrium constant for a weak acid can be expressed through the equation…

Answer 20

Question 21

What is pka?

Answer 21

The log of Ka. It is used to measure the strength of weak acids.

Question 22

How do you calculate pKa?

Answer 22

• log Ka

Question 23

The lower the pKa….

Answer 23

…the stronger the acid

Question 24

Give the equation for the equilibrium constant of a base, Kb.

Answer 24

Question 25

What does pKb measure? How do we calculate it?

Answer 25

Used to measure the strength of the base. -log Kb

Question 26

Lower the pKb….

Answer 26

the stronger the base

Question 27

pKa and pKb of a conjugate acid-base pair are linked by the following expression….

Answer 27

pKa + pKb = pKw

Question 28

pKw is the negative log of….

Answer 28

Kw- the dissociation product of water

Question 29

At 25 degrees Celsius, pKw is…?

Answer 29

14

Question 30

What is an amphoteric electrolyte? Give an example

Answer 30

Functions as both an acid and a base. Eg. amino acids.

Question 31

What is a zwitterion?

Answer 31

A molecule with both a positive and negative charge

Question 32

Show equations of amino acids as an acid and base to show that they are amphoteric electrolytes/zwitterions

Answer 32

Question 33

Polyprotic acid? Give 2 examples.

Answer 33

acid capable of donating more than one proton. Citric acid and phosphoric acid

Question 34

What is a polyprotic base? Give an example

Answer 34

A base that is capable of accepting one or more protons

Question 35

For polyprotic acids, each stage of dissociation can be presented by an equilibrium expression. Each stage has a specific pKa and pKb. Give the equations for phosphoric acid. What does the dissociation constant decrease?

Answer 35

• Dissociation constant decreases because the base formed is more and more negative, so it holds onto the proton more strongly. Not very good at letting it go/ cant donate.