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Definition and Determination of pH

Physical

A2

Acids & Bases

AQA Content

Convert the concentration of hydrogen ions into pH and vice versa
Calculate the pH of a solution of a strong acid from its concentration.

Specification Notes

The concentration of hydrogen ions in an aqueous solution covers a very wide range. Therefore, a logarithmic scale, the pH scale, is used as a measure of hydrogen ion concentration.


Notes

To convert the concentration of hydrogen ions to pH, use the formula:


where [H+] is the concentration of hydrogen ions in moles per cubic decimetre. For example:
To convert pH to the concentration of hydrogen ions, use the formula:


Many problems in exams need you to find hydrogen concentration by reaaranging the acid dissociation equation and use the answer to fins the pH. You would use:

then:

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