What is the meaning of ‘p’ and ‘H’ in the pH?

The pH scale is a logarithmic scale that indicates the concentration of hydrogen ions (H⁺) in a solution. It works inversely, meaning a higher concentration of hydrogen ions corresponds to a lower pH value.

The pH is calculated using the formula:

pH = -log [H⁺]

This formula shows that pH is the negative logarithm (base 10) of the hydrogen ion concentration in the solution.

Origin of the pH Concept

The concept of pH was introduced by Sørensen in 1909. In the term “pH”:

• ‘p’ stands for the potential or power of hydrogen
• ‘H’ stands for hydrogen

Measuring pH

pH can be measured using litmus paper, which helps identify whether a solution is acidic or basic. Besides litmus, plant-based indicators are also used, as many plants contain pH-sensitive pigments. Examples include:

• Hibiscus
• Red cabbage
• Grapes

Examples of Acidic Substances

For instance, citrus fruit juice is acidic because it contains citric acid. Other carboxylic acids are also found in many living systems.