Uses in Chemistry
Logarithms can be used in the classroom to calculate the concentration of ions present using either the pH or the pOH of an aqueous solution.
The pH is the measure of the concentration of Hydrogen ions present in an aqueous solution
The pOH is a measure of the concentration of HydrOxide ions present.
As the pH decreases, the concentration of hydrogen ions increases, so the solution becomes more acidic.
As the pH increases, the concentration of hydroxide ions increases, making the solution more alkaline.
NOTE: the pH is equivalent to the power the ten is raised to.
pH [ H+(aq)]
mol per litre
7 1x10-7 6
Using the logarithms
By applying the formulas pH = -log10[ H+ (aq)] and pOH = -log10[ OH- (aq)], the concentrations can be calculated.
pH = 3 pH = -log10[ H+ (aq)]
3 = -log10[ H+ (aq)] so therefore the H+ concentration
-3 = log10[ H+ (aq)] is 1x10-3 which by comparing it
10-3 = [ H+ (aq)] with the table is correct!
Other useful formulae
A brief history of John Napier Rules of Logarithms Examples of Logarithms
- [H+ (aq)] = 1x10-7 moll-1 = [OH- (aq)] in an neutral solution
- pH + pOH = 14
- [H+ (aq)] = 10-pH
Answers to Examples Uses of Logarithms