pH: Log relationship

Basic, Basic Sciences

The pH scale is used to represent hydrogen ion concentration in solution. The range of possible hydrogen ion activity spans many orders of magnitudes from roughly 10 M to 10-15 M. The pH of a solution can be calculated using the equation:  

pH = -log[H+]

In order to easily represent this wide range of activity, a logarithmic scale, which uses orders of ten, is used. As an example, a solution with a pH of 4 has a hydrogen ion activity that is 10 times greater than a solution at a pH of 5. On the pH scale, a value of 7 represents a neutral solution while a pH above 7 is basic, and below 7 is acidic.


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Aaron Lloyd, MD