So we can hardly wrap up speaking about chemistry
without addressing acids, bases and buffers.
The pH scale is at the base of that. We could
have the pOH scale but in biology we generally
stick to the pH scale which is a measure of
hydrogen ion concentration in a solution.
pH is a measure of the -log of hydrogen ion
concentration in mols in a solution.
So each level we change in pH, say from 7 to 6
is actually a 10 times change, or an order of 10
in magnitude more or less of hydrogen ions in
the solution. So, each step up is actually
a very large step. If we look at the pH scale,
you're probably quite familiar with the fact that
lemons are quite acidic and household bleach or
shampoos are quite basic. But all this has to do with
is greater or lesser hydrogen ion concentration.
Something that is acidic has more hydrogen ions
in solution. And something that is more basic has
more hydroxide ions or less hydrogen ions in solution.
So water is the perfect neutral molecule because
it has an equal amount of hydroxide and hydrogen
in solution. Just as water molecules are constantly
reassociating with each other because of the slight
positive and negative charge, hydrogen and
hydroxide ions are also separating, not quite as much.
But that lends itself to being completely neutral
because there is an equal number of hydrogen ions
as there are hydroxide ions in the solution.
And hence, water has a neutral pH of 7.
Again, in biology we stick with the pH scale rather
than the pOH scale. And so we have a measure of
pH 1 through 14. 1 being very acidic and 14
being very basic with water right in the middle at 7.