Lecture 6 - Using pKa Values Flashcards
Ka =
[acid product 1] x [acid product 2] / [acid]
pKa =
(-log) x Ka
∆Ga =
(2.3) RT log Ka
if a base is weak its conjugate acid is…
strong
if a base is strong, its conjugate acid is…
weak
pKa is a logarithmic scale, what does this mean?
it mean that between each integer, the values differ from one another by a factor of ten
K(eq):
(equilibrium constant)
10 ^(pKa on left - pKa on right]
how can you determine the equilibria values in acid-base reactions?
determine by comparing pKA of both acids
what side of the equilibria is favoured more?
the side with the weaker acid and weaker base is favoured
amphoteric behaviour of water as a base:
the pKa of the acid must be <0
amphoteric behaviour of water as an acid:
the conjugate acid must have a pKa value >14
standard free energy of ionization of an acid is directly proportional to…
the pKa
the henderson-hasselbach equation:
pH = pKa + log [A] / [HA]
or
A = pH - pKa = log [A] / [HA]
what does the Henderson-Haselbach equation allow you to do?
allows you to calculate the protonation state from pKa values
pKa values you should know:
water = 14
methanol = 15.5
hydronium ion = 0
ammonium = 9.25
acetic acid = 4.76
