2009 p3 qn 1a bi)
given pka of glutamic acid is 4.3
of course many of us know the COOH R group of glutamic acid will
be deprotonated above pH of 4.3
i know pH above 4.3 is alkaline relative to the pka of 4.3 of
glutamic acid
but i cant answer when my friend ask me why
why a pH above the pka of an acidic(cooh) group will cause it to
be deprotonated?
no good definition of pka online
how to answer the above question using chemistry concepts using
chemistry terms?
For every acidic group (this includes the conjugate acids of basic
groups), there will be a specific pH of the solution in which
you've equal molarities of conjugate acid and conjugate base (for
this particular acidic group), correct? (this is common sense).
Chemists call this pH (which is unique for all acidic groups)
the pKa value (for this particular acidic group).
Hence, when pH starts getting more alkaline, you get higher
molarity of conjugate base, lower molarity of conjugate acid.
Hence, when pH starts getting more acidic, you get higher molarity
of conjugate acid, lower molarity of conjugate base.
If you and your friend still don't understand after reading the
above, then you and your friend have no chemistry sense, no hope
liao.
And bear in mind this is about equilibria, which means no matter
what the pH is, you'll always have some molarity of all possible
conjugate acids and conjugate bases, eg. H3A2+, H2A+, HA, A-, etc,
it's only a matter of correctly identifying the major species
present at any given pH for A levels (at Uni levels, you need to
identify the 1st most major species, the 2nd most major species,
the 3rd, and so on, at any given pH).
