A pH scale is used to measure the degree of acidity or alkalinity of a solution. A more formal definition of pH is the negative logarithm of the hydrogen ion activity of a solution {pH = - log [H+] }. Essentially, pH expresses the degree of hydrogen ion activity in an acid or a base.

  One simple way to understand pH is to visualize it on a scale ranging from 0 to 14. Acidic solutions range from 0 to 7 on the pH scale, with the lower numbers representing a strong acid. Basic solutions range from 7 to 14, with the higher numbers representing a strong base. Therefore, the pH of solutions become more acidic when more hydrogen ions are added to a solution. Conversely, when substances with more hydroxide ions are added to a solution, the pH becomes more alkaline.

A pH of 7.0 is considered to be neutral, and is very safe to handle. In fact, any chemical in the pH range of 3.0 to 10.0 can be safely handled without risk to exposed skin. However, it should be carefully noted that any chemical with a pH value lower than 3.0 or higher than 10.0 should be handled with great care. It is also strongly recommended that you should wear gloves and eye protection when you are dealing with any laboratory chemicals.

Next, we will look at some methods of pH measurement and consider some basic questions.