What is the difference between pH and hydrogen ion concentration?

The hydrogen ion concentration is the number of moles of ##"H"^+## ions in a litre of solution.

The concentration can range from about ##"10 mol/L"## to about ##10^(-15) "mol/L"##.

To convert such a wide range of numbers into ones that are easier to visualize, chemists take the negative logarithms of the concentrations.

See

This gives numbers ranging from about -1 to +15.

If you know the concentration, you can calculate the .

EXAMPLE 1

Find the pH of a solution in which ##["H"^+] = "0.0025 mol/L"##.

Solution

##"pH" = -log["H"^+] = -log(0.0025) = 2.60##

If you know the pH, you can calculate the hydrogen ion concentration.

EXAMPLE 2

Calculate the hydrogen ion concentration for a solution with pH 2.30.

Solution

Since ##"pH" = -log["H"^+]##,

##["H"^+] = 10^"-pH" " mol/L"##

So ##"H"^+] = 10^-2.30 "mol/L" = 5.0 × 10^(-3) "mol/L"##