3.06 pH Scale

pH Scale

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Logarithmic Scale

Pure water has an equal number of positive ions and negative ions (H⁺ and OH^-) so it is neutral. The pH of 7 is a measure of the concentration of ions present. It is based on the logarithm of the power of ten, which is the exponent of a number in base ten.

This means that each increase or decrease on the pH scale represents a tenfold (10x) increase or decrease. For example:

• A pH reading of 5 is actually 1/10th the acidity of a pH reading of 4. This means it is also 1/100th the acidity of a pH reading of 3.


• If we look at the other direction on the scale, a pH reading of 5 is 10 times the acidity of a pH reading of 6 and a 100 times the acidity of a pH reading of 7.

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Indicators

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