What is the difference between pH and hydrogen ion concentration?

1 Answer
Aug 20, 2014

Answer:

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.

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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"#