pH and Ionization Flashcards
What is pH?
- pH of a solution is a measure of free hydrogen ion (“proton”) concentration
- pH is a log scale of proton concentration [H+]
What is the importance of pH in biological systems?
pH can
affect electrostatic interactions (bonding) which can then affect the structure and function of a
biomolecule.
What is the dissociation of water?
What does the equilibrium constant, Keq, measure?
the extent to
which reactants are converted to products by the
reaction at equilibrium.
What does equilibrium mean?
the point where the concentrations of the reactant(s) and product
are unchanging with time, because the forward and backward reactions have the same rate.
What is the equilibrium constant for the dissociation of water?
What is the equation that relates pH to hydrogen ion concentration?
When an acid loses a hydrogen ion
(“unprotonated”), it forms:
ionized, conjugate base
when a base gains a hydrogen ion
(“protonated”), it forms:
ionized, conjugate acid
Henderson-Hasselbach equation allows us to
correlate:
pH and pKa
What is the Henderson-Hasselbach equation?
What can you calculate with the Henderson-Hasselbach equation?
the relative amount
of protonation of acids/bases in a given pH.
pKa is the pH at which the acid is…
-half-associated, or
- half-dissociated, or
- half-protonated, or
- half unprotonated.
Given the pKa and pH, you can predict the proportion of
the molecule that is protonated (or UNprotonated). Why is this important?
Physiologically, enzymes function (optimally) at a given pH. This is due
to having the correct protonation states of certain functional groups
on the enzyme. If a functional group(s) is not protonated correctly (e.g., in the wrong pH), the enzyme
will not function properly.
What is a buffer? Where is it most effective?
Acid-base conjugate pairs that resist changes
in pH. In otherwords, a buffer is most effective at the vicinity of its pKa .
