3: Buffers Flashcards
formula for the autoionization of water
2 H2O <———> H3O+ + OH-
write the equilibrium constant expression, Kw
Kw = [H3O+]aq [OH-]aq = 1.0 * (10^-14) at 25 degrees Celsius
[H3O+]aq = [OH-]aq = 1.0 * (10^-7)
formula for pH
pH = -log[H3O+]aq
describe the pH scale
pH = 7.0 (neutral
pH < 7.0 (acidic)
pH > 7.0 (basic)
formula for pKa
pKa = - log (Ka)
formula for acid dissociation constant, Ka
Ka = ([conc. of conjugate base][conc. of H+]) / [conc. of reagent weak acid]
formula for pKa
pKa = -log Ka
identify the predominant species in the solution when:
- pH of solution < pKa of weak acid
- pH of solution = pKa of weak acid
- pH of solution > pKa of weak acid
pH of solution < pKa of weak acid - weak acid (HA)
pH of solution = pKa of weak acid - both HA and A-
pH of solution > pKa of weak acid - conjugate base (A-)
!!! SEE EXAMPLES IN MODULE !!!
in which part of the titration curve does pKa corresponds to
inflection point
identify the predominant species in the solution when given the following in a titration curve:
- pH of solution < pH at inflection point
- pH of solution = pH at inflection point
- pH of solution > pH at inflection point
pH of solution < pH at inflection point - weak acid (HA)
pH of solution = pH at inflection point - both HA and A-
pH of solution > pH at inflection point - conjugate base (A-)
!!! SEE EXAMPLES IN MODULE !!!
solutions that resist drastic change in pH and useful in mimicking the conditions inside the cell
buffers
composition of buffers
- weak acid + salt of its conjugate base
- weak base + salt of its conjugate acid
(both must be present in appreciable concentrations)
physiological pH range
6.4-7.6
ability to resist drastic pH changes
buffering action
write the dissociation equation for a buffer made up of weak acid and its conjugate base
HA (aq) + H2O (l) <————> A- (aq) + H3O+
write the dissociation equation for a buffer made up of weak base and its conjugate acid
B (aq) + H2O (l) <———-> BH+ (aq) + OH- (aq)
addition of small amount of strong acid results to:
increase in [H3O+] in the solution —- counteracted by a neutralization reaction with the basic component of the buffer system
addition of small amount of strong base results to:
increase in [OH-] in the solution —- counteracted by a neutralization reaction with the acidic component of the buffer system
write the neutralization reaction of a buffer system when a strong base is added to the solution
OH- (aq) + HA (aq) ————> A- (aq) + H2O (l)
or
OH- (aq) + BH+ (aq) ————-> B (aq) + H2O (l)
give the Henderson-Hasselbach equation
pH = pKa + log [A-]/[HA]
what happens when pH = pKa (maximum buffering capacity)
- weak acid is exactly half-neutralized
- equal amounts of weak acid and conjugate base
pH range in which the buffer is effectively resisting drastic pH changes or where the buffer’s capacity to resist change is at maximum)
buffering region (pKa +- 1)
mass of solid reagent formula
mass of solid reagent = C * V * f * MM
mass of solid reagent formula
mass of solid reagent = C * V * f * MM
C- concentration of buffer solution in M
V - volume of buffer solution in L
f - fraction of component in the buffer system
MM - molar mass in g/mol
volume of liquid reagent formula
volume of reagent = m/p = (C * V * f * MM) / p
p - density in g/ml
volume of component formula
volume of component = [(Cbuffer * Vbuffer)/Cstock)] * f
