pH Calculator
One unit is tenfold — lemon juice at pH 2 is ten thousand times more acidic than coffee at pH 6.
The formula
pH = −log₁₀[H⁺]; pH + pOH = pKw, which is 14 only at 25 °C
A logarithm, so the steps are enormous
Each pH unit is a factor of ten in hydrogen ion concentration.
Lemon juice at pH 2 and coffee at pH 6 differ by four units, which is ten thousand times. Reading the scale as though it were linear makes every comparison wrong by orders of magnitude, and it is the commonest misunderstanding in chemistry.
Seven is not neutral in general
Neutral means [H⁺] equals [OH⁻], and where that lands depends on how readily water ionises.
Water ionises more when warm, so neutral pH falls to about 6.6 at 50 °C and 6.1 at 100 °C. Water at 6.6 and 50 °C is exactly neutral and would read as acidic to anyone who had memorised the seven.
The scale is not bounded at 0 and 14
Those are simply where common aqueous solutions sit.
Concentrated strong acids reach negative pH and concentrated bases exceed 14. Nothing in the definition stops them; the range is a convention of everyday chemistry rather than a limit of the mathematics.
Standard atomic weights are averages
The masses used here are weighted means over the isotopes found naturally on Earth, which is why chlorine is 35.45 rather than a whole number.
For work with a specific isotope, or with material from an unusual source, the isotopic mass is the right figure and it is not this one.