Lecture 8 - Acid-Base theory, pH, pKa and pKb 1 Flashcards
Give three examples of drugs that are weak organic acids
Aspirin, ibuprofen, diclofenac.
Give three examples of drugs that are weak organic bases
morphine, procaine, chloramphenicol
Salts that are drugs
Sodium ibuprofen
Why is the extent of ionisation of a drug important?
It has an effect on its absorption, distribution and elimination.
What is a bronsted lowry acid?
proton donor
What is a bronsted lowry base?
proton acceptor
Strong acids/bases fully….
ionise
Give the equation for the complete dissociation of HCl.
HCl –> Cl- + H+
Weak acids/bases partially ……..
ions
Weak acids only…
partially dissociate.
Give the equation of the partial dissociation of the weak acid ethanoic acid
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?
ampholyte/amphiprotic solvent
Give the equation for water as a Bronsted lowry base…
What is a conjugate acid-base pair?
Species which are interchangeable by the movement of a single proton
Give the equation for the dissociation of ethanoic acid in water and label the conjugate acid-base pairs.
In conjugated acid base pairs, are the acid and base strong or weak?
weak
In an aqueous solution, how do we represent the dissociation of a weak acid?
HA+H2O ⇌ A^- +H3O^+
- HA= acid 1, A^- = base 1
- H2O = Base 2, H3O^+ = acid 2
The dissociation of a weak base can be represented in two ways…
Give the simplified equation for the dissociation of a weak acid. Why is the water removed?
The equilibrium constant for a weak acid can be expressed through the equation…
What is pka?
The log of Ka. It is used to measure the strength of weak acids.
How do you calculate pKa?
- log Ka
The lower the pKa….
…the stronger the acid
Give the equation for the equilibrium constant of a base, Kb.
What does pKb measure? How do we calculate it?
Used to measure the strength of the base. -log Kb
Lower the pKb….
the stronger the base
pKa and pKb of a conjugate acid-base pair are linked by the following expression….
pKa + pKb = pKw
pKw is the negative log of….
Kw- the dissociation product of water
At 25 degrees Celsius, pKw is…?
14
What is an amphoteric electrolyte? Give an example
Functions as both an acid and a base. Eg. amino acids.
What is a zwitterion?
A molecule with both a positive and negative charge
Show equations of amino acids as an acid and base to show that they are amphoteric electrolytes/zwitterions
Polyprotic acid? Give 2 examples.
acid capable of donating more than one proton. Citric acid and phosphoric acid
What is a polyprotic base? Give an example
A base that is capable of accepting one or more protons
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?
- 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.
