Introduction to pH
A pH measurement of a medium is a measure of how acidic or how basic it is. Lemon juice or vinegar for example are acidic, whereas bleach or sodium bicarbonate are basic (the opposite of acidic). pH can be imagined as a measure of the presence of hydrogen ions or H+ in the medium or the ability of the medium to produce H+ ions. An acid produces H+ ions whereas a base absorbs H+ ions. In more technical terms pH is defined as a negative decimal logarithm of the hydrogen ion activity in a solution. Using this definition, a pH value of 7 corresponds to a neutral solution, neither acid nor basic. A pH value < 7 corresponds to an acidic medium, and a pH value > 7 corresponds to a basic solution. Anyways, the reason you care about all this is that biological systems are very sensitive the pH of their environment. Whether or not fish survive in a lake or whether your fermentation goes well for your latest beer batch depends on the pH. So it it is kinda important. You can read a lot more about pH by googling around.