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Chemistry Revision for WAEC students: How to calculate potential of hydrogen [pH and pOH]

Potential of Hydrogen

pH is a unit of measurement often used in fundamental chemistry concepts. “How to Calculate pH” explains it’s categories the scientific mathematics and role pH has in our lives.

Terms to Be Familiar With:



-Hydrogen ion

-Hydroxide ion



What is pH?

The term “pH” is an abbreviation for the “potential of hydrogen.” pH is a unit of measurement which represents the concentration of hydrogen ions in a solution. This unit was introduced by biochemist Søren Peter Lauritz Sørensen in 1909. It was an easy way to represent the concentration of hydrogen ions in a solution during titrations. When an acid or base is added to water, that compound dissociates into ions. For acids one of those ions is a hydrogen ion (H+) and for bases one of the ions is a hydroxide ion (OH–). This description of acids and bases is known as the Arrhenius Theory. The concentration of hydrogen ions are often described by the pH scale as a numeric value.

The pH Scale: Acidic, Neutral, and Basic

The pH scale describes the acidity of the solution: acidic, neutral, or basic A solution with a pH less than 7 is an acid, exactly 7 is a neutral solution, and above 7 is a base. Bases have less hydrogen ions but more hydroxide ions, represented by the pOH or “potential of hydroxide ions.”

Acidic. Neutral. Basic

Less than 7 7 Greater than 7

Many other scientists studied the proprieties of acids and bases from the ideas of Sorensen and Arrhenius and came up with their own definitions. A notable theory is known as the Bronsted-Lowry Theory. The Bronsted-Lowry Theory is a concept involving acid and bases which suggest that acids act as proton donors. Since neutral hydrogen atoms are usually made of one proton and one electron, a positive hydrogen ion is often referred to as a proton. These protons carry a positive charge and are given away to the bases. Bases, with that logic, are proton acceptors. Bases, carrying lone pairs of electrons, attract positive hydrogen ions (protons).

In the lab, pH can be determined by a pH indicator such as pH paper. pH paper usually contains a weak acid or a weak base which will respond by changing color at a specific pH. This method is used frequently as a cheap, quick way to determine pH rather than using pH meters which need frequent calibration and maintenance. Keep in mind that very low or very high pH value solutions can be very caustic and should be handled with care.

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Hydrogen Søren Peter Lauritz Sørensen WAEC


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