Origin of pH: Søren Sørensen's 1909 'Potential of Hydrogen' Scale

In 1909, Danish chemist Søren P. L. Sørensen introduced the pH scale at the Carlsberg Laboratory. pH stands for potentia hydrogenii (Latin for "potential of hydrogen")—or "power of hydrogen." It quantifies the acidity or basicity of an aqueous solution as the negative base-10 logarithm of the hydrogen ion activity: pH = -log₁₀[H⁺].

The scale runs 0–14: acidic (<7), neutral (7), basic/alkaline (>7). It revolutionized chemistry, biology, medicine, and industry by providing a universal, quantitative measure of acidity.