pH definition formula

Definition

pH is defined mathematically as pH = -log10[H+], the negative base-ten logarithm of hydrogen ion molar concentration. The formula tells how the number is calculated but not why it matters.

Counting decimal places gives the value: a concentration of 10 to the minus 7 mol/L corresponds to pH 7. Each whole-number step on the scale reflects a tenfold change in hydrogen concentration. The definition alone does not convey that hydrogen is a bare proton tied to hydroxide by a constant.

Related concepts

pOH · pH · Logarithmic scale

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Part of The Blueprint of Water · 📏 measurement