What is pH
pH is a measure of the hydorgen ion concentration of a solution. Solutions with a high concentration of hydrogen ions have a low pH and solutions with a low concentrations of H+ ions have a high pH. This may seem like a confusion way to express these reationships, and it is, until you understand what pH stands for. The equation that defines pH is given as follows:
which is read:
the pH is equal to minus the log of the H+ concentration.
For example is the H+ concentration is very low, lets say about 0.0000001M, then the pH is
pH= -log[.0000001] whis is the same as -log[1 X 10-7]
the term log[1 X 10-7] = -7
- (-7) = 7
Look at the following table
hydrogen ion concetration pH solutions with a pH of
.01M 2 coke and orange juice
.00001 5 black coffee
.0000001 7 pure water
.000000001 9 baking soda
.000000000001 12 household bleach
.0000000000001 13 oven cleaner
From this table you will notice a few relationships
a difference of one pH unit (ie from pH 2 to pH 3) is a ten fold (10X) difference in H+ ion concentration.
pure water should have a pH of 7.0
solutions with a pH below 7.0 are termed acidic and solutions with a pH above 7.0 are termed basic.