Acidity or alkanity of a solution is expressed by its pH value, which is defined as (where, [H⁺] = hydrogen ion concentration in the solution).

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The pH value of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration ([𝐻+][H+]) in the solution. Mathematically, it is expressed as: pH=−log⁡10[𝐻+]pH=−log10​[H+] This equation quantifies the acidity or alkalinity of a solution based on the concentration of hydrogen ions present. A lower pH value indicates a higher concentration of hydrogen ions, signifying a more acidic solution. Conversely, a higher pH value indicates a lower concentration of hydrogen ions, indicating a more alkaline (basic) solution. The pH scale typically ranges from 0 to 14, where pH values below 7 are acidic, pH 7 is neutral (indicating equal concentrations of hydrogen ions and hydroxide ions), and pH values above 7 are alkaline.