Ph Scale – How Atoms Come Together to Form a Molecule

00:00 So we can hardly wrap up speaking about chemistry without addressing acids, bases and buffers.

00:06 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.

00:19 pH is a measure of the -log of hydrogen ion concentration in mols in a solution.

00:29 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.

01:17 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.

01:42 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.

01:54 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.