Acid/Bases Flashcards
chemical equilibrium is
dynamic
Law of mass action
A +B –> C + D
Vf=
vf = kf[A][B]
V r=
vr = kr[C][D]
equilibrium constant Keq =
Keq = kf / kr = [C][D] / [A][B]
Water is in equilibrium with its
component ions H+ and OH-
pH Cytosol
6.9
pH Gastric juice
1.4 -3.0
pH of urine
5-8
An acid is a compound or chemical group that acts as a
proton donor
An base is a
compound or chemical group that acts as a proton acceptor
The equilibrium between and acid and its conjugate base in aqueous solution,
HA +H2O –> H3O+ + A- ,
is usually abbreviated to HA –>H+ + A-
Strong acids like HCl and bases like NaOH are
completely dissociated in water whereas weak acids and bases are reversibly protonated and deprotonated.
Many drugs, amino acids, peptides, proteins and nucleic acids are
weak acids or bases.
The strength of an acid or base is a measure of
its propensity to either donate or accept protons measured as its pKa
the _____ the pKa, the stronger the acid
lower
the _____ the pKa, the strong the base
higher
pKa =
-log Ka = - log ([H+] [A-]/[HA])
Ka =
[H+] [A-]/[HA]
examples of medically important weak bases
purine: amphentamines
procainamide
pyrimides: nortiptylene
local anesthetics
pH strongly affects
enzymatic activity
pH also affects
drug availability
For drugs with ionizable groups, a critical factor governing uptake and excretion will be the
pH of the local environment.
When an acid or base is 50% deprotonated and 50 % protonated then
pH=pKa