Question

What is the difference between pH and hydrogen ion concentration?

Answer 1

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

Explanation:

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 What is pH?

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

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

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"`