Lecture 4: Acid and Bases Flashcards
What does acid and base properties influence?
biodistribution (eg. solublity) and partitioning characteristics (eg across membranes)
What are acids?
Acid – proton (H+) donor; An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance
What are bases?
Base - proton (H+) acceptor; A base is a molecule or ion able to accept a hydrogen ion from an acid.
Why is water amphoteric?
Water (H2O) can function both as a proton acceptor (base) and a
proton donor (acid). Hence water is known as an amphoteric
substance.
ThWhat is a strong acid or base?
These are substances that are completely ionized in solution. [n, i.e. equilibrium lies far to the right (products)]
What is a weak acid or base?
These are substances that are partially or incompletely ionised in solution. [ i.e. equilibrium lies more to the left (reactants).]
What does the pKa (= -log of Ka) value indicate?
values are used to indicate acid strength
What does a low pKa (< 7) values indicate for a drug?
this means stronger acid and bases
What does a high pKa (>7) values indicate for a drug?
This means a weaker acid and base.
What is the Henderson Hasselbalch equation?
pH = pKa + log 10 ( [A-] / [HA] )
What does [HA] represent in the Henderson Hasselbach equation?
concentration of an acid
What does [A-] represent in the Henderson Hasselbach equation?
the concentration of conjugate base
How do we find the Ionisation % of the HA type drugs?
100/ 1+10^ (pKa - PH)
How do we find the Ionisation % of the BH+ type drugs?
100/ 1+10 ^ (pH-PKa)
What happens when pH = pKa of a drug?
the drug is 50 % ionized and 50 % unionized in aqueous solution
