What+is+pH?

A pH scale is used to measure the amount of acid in a liquid-like water. Because acids release hydrogen ions, the acid content of a solution is based on the concentration of hydrogen ions and is expressed as "pH." This scale is used to measure the acidity of rain samples.

0 = maximum acidity 7 = neutral point in the middle of the scale 14 = maximum alkalinity (the opposite of acidity)

The **smaller** the number on the pH scale, the more **acidic** the substance is. Rain measuring between 0 and 5 on the pH scale is acidic and therefore called "acid rain." **Small** number changes on the pH scale actually mean **large** changes in acidity.