Hi UltimaOnline, just a little concept clarification. Is there a
buffer region for weak acid and weak base titration? Thanks
Technically, yes. Buffer regions still occur when you've close to
equal molarities of HA and A-, as well as close to equal molarities
of B and BH+ (note that the actual maximum buffer capacities of the
solution, however, is no longer based simplistically on having
equal molarities of both members of each conjugate acid-base pair,
since the other conjugate acid-base pair also exerts its influence
on pH and buffering capacity; exact calculations here are
significantly beyond the scope of A levels).
In addition, there is an additional (albeit weaker) buffer
region (unique to weak acid - weak base titrations) that spans from
the 1st buffer region (ie. near half-equivalence point) all the way
to the 2nd buffer region (ie. near double-equivalence point),
including the titration equivalence point, since both cation and
anion of the salt at equivalence point, are themselves a weak acid
and a weak base.
If Cambridge were to ask Singapore students to calculate the pH
at equivalence point of a weak acid - weak base titration, 99.99%
of Singapore H2 Chem students (and even many JC teachers and
private tutors) would die. But if you're interested to challenge
yourself, try solving such a question. Hint : you'll need to solve
simultaneous equations which takes into account the simultaneous
hydrolysis of both cation and anion of the salt.
