Neutral pH

Definition

Neutral water is the condition where hydrogen and hydroxide concentrations are equal. At 25 degrees Celsius this falls at pH 7 because each concentration equals 10 to the minus 7 mol/L.

Seven is not an arbitrary or lucky number; it falls straight out of the measured behavior of water and the value of Kw. Neutrality is defined by the equality [H+] equals [OH-], not by any fixed pH value. As temperature changes the neutral pH moves while the equality condition still holds.

Related concepts

Self-ionization of water · Temperature dependence of neutral pH · Self-ionization constant of water

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Part of The Blueprint of Water · 🧪 chemistry