Interactive pH scale

Every textbook says one pH step means a factor of ten - you only feel it at the slider. This scale converts every value into concentrations live and shows which everyday substances sit there. The full list is in the pH values table.

What the pH value measures

The pH value is the negative decadic logarithm of the hydrogen-ion activity: pH = −log₁₀ a(H⁺). Put simply, it counts the zeros of the H⁺ concentration. Pure water at 25 °C contains 10⁻⁷ mol/l - hence pH 7. How a glass electrode turns this concentration into a measurable voltage is explained in the basics.

The logarithm in numbers

Cola (pH ≈ 2.5) thus contains about 16,000 times more H⁺ ions than fresh milk (pH ≈ 6.7) - although only a good four scale steps separate them.

Neutral shifts with temperature

The neutral point sits exactly at pH 7 only at 25 °C. With rising temperature, water dissociates more strongly, the ion product pKw falls - and with it the neutral pH. Hot water at 60 °C is neutral at pH 6.5, not acidic. For measuring practice this means: always keep the temperature in mind; how it affects slope and buffers is calculated by the electrode check.