# What is the difference between pH and hydrogen ion concentration?

Aug 20, 2014

The hydrogen ion concentration is the number of moles of ${\text{H}}^{+}$ ions in a litre of solution.

#### Explanation:

The concentration can range from about $\text{10 mol/L}$ to about ${10}^{- 15} \text{mol/L}$.

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 $\text{H"^+] = 10^-2.30 "mol/L" = 5.0 × 10^(-3) "mol/L}$