Quick Review of pH
The pH scale is a logarithmic scale that gives a measure of acidity.
The acidity of a solution is related to the H+ ion concentration. Normally, this gives very small values.
The pH scale was designed to give workable values, and is based on the dissociation constant of water
(H2O).
The opposite of acidity is basicity (or alkalinity), and depends on the OH- ion concentration. You can see,
when water dissociates, it forms the following equilibrium:
H2O <--> H+ + OHThe amount of molecules that do this is 1 × 10^-14 of the total number of water molecules. Since one
molecule generates one of each ion, their concentrations will be equal.
To measure pH, the H+ concentration is measured, and converted into logarithmic form. The formula is:
pH = -log(base 10) [H+].
The brackets mean concentration
if the pH is lower than 7, the initial concentration will have been more than the corresponding OHconcentration, and so the solution is acidic. If the pH is equal to 7, both ions are in equal concentration
and the solution is neutral. If the pH is higher than 7, the solution is basic.
So:
pH 7 is neutral, neither acid nor alkaline
pH 1 is the most acidic
pH 14 is the most alkaline
Since the equation is LOGARITHMIC each pH value represents 10X less H+ ions then the next higher
value. Going from a pH of 1 to a pH of 2 means 10X less H+ ions. (this is less acidic or more basic))
Going from a pH of 1 to a pH of 3 means 100X less H+ ions.
Going from a pH of 5 to a pH of 3 means 100X more H+ (this is more acidic or less basic)
The highest concentration of H+ ions in an acid is at pH of 1
The opposite of pH is pOH which represents the concentration of OH (hydroxyl ions) in a solution but we
usually express both acids and bases with pH.
How does the concentration of H+ get higher with lower pH numbers?
-log(base 10) [H+] means
1/+log(base 10) [H+]
Ex: pH of 2 = 1/100 = 0.01 moles H+/litre
pH of 1 = 1/10 = 0.1 moles H+/litre
Which has the higher value?