The pH scale is used to describe the strength of acids or bases. Substances with a pH less than 7 are acids. Substances with a pH greater than 7 are bases. You can judge the strength of an acid or base by how far its pH is from 7. Substances that have very low pH, such as a pH of 1, are very strong acids. Substances that have a very high pH, such as a pH of 14, are very strong bases.

Substances that are neither acids nor bases are neutral. Neutral substances have a pH of 7. You can neutralize a base by adding acid, and you can neutralize an acid by adding base. However, you have to be careful not to add too much because you can go past neutral very quickly.