What does pH stand for and
the formula for calculating pH

To answer what does pH stand for is pretty straight forward. The "p" stands for potential and "H" stands for hydrogen.

Calculating pH

The definition of pH is the negative logarithm of the hydrogen (H+) ion activity in a given solution. By virtue of its logarithmic nature, pH is a dimensionless quantity. The purpose of the negative sign in the equation is to give a positive pH value.

Being a logarithmic scale means that a change by a factor of ten in the H+ activity brings about a change of one unit on the pH scale. The range of the pH scale is from 0 to 14. However, in some cases pH values can be negative or higher than 14. pH 0 is extremely acidic and pH 14 extremely alkaline. Neutral solution is defined as the one in which the activity of H+ and OH- is identical.

The pH value depends on the temperature

It is commonly assumed that a neutral solution has a pH of 7.00. In most cases that's a very good approximation, but it is true only for 25°C. If the temperature increase above 25°C the pH of a neutral solution will decrease below 7. And if temperature decrease below 25°C, the pH value will increase above 7.

As you will see in the section ""The pH versus temperature relation"," temperature is an important parameter to consider in pH measurements.


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