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
A buffer is a mixture of
a weak acid HA
and its conjugate base A-
The____marks a “speedbump” in the titration curve
of a weak acid or base
pKa
The _____ buffer system is the most important regulator of extracellular pH.
bicarbonate
H-H equation for bicarbonate
pH = 6.1 + log [HCO3-]mM/ .03Pco2mmHg
normal Pco2=
40mmHg,
normal [CO2]d =
1.2 mM.
Normal [HCO3-] =
24 mM
Bicarbonate buffer rxn 2 is catalyzed by
carbonic anhydrase
The bicarbonate buffer system is OPEN modulated by regulation of
CO2 loss in the lung and H+ /HCO3- excretion in the kidney allowing the system to be an effective buffer 1.3 units above its pKa
[A-] is the
concentration of the proton acceptor (base)
[HA] is the
concentration of the proton donor (acid).
pH of arterial blood: =
7.4
pH of venus blood: =
7.3
[HCO3-] is ____
24mM
pCO2 =
40mmHg
Weak acids and their conjugate base exist as
2 equilibrium reactions that oppose and thereby stabilize each other.
As base is added, it can be
protonated by the acid and turned into water.
As acid is added, it can be
deprotonated by the base or taken up by the base to form a neutral product.
In the buffering range, the addition of acid or base has
little impact on the pH of the solution, as seen on a titration curve.
