This whole lesson is on the pH scale. It deals with substances that are acids, bases, and those that are neutral. The pH scale is a way of measuring the acidity of a substance whether it be a base or an acid. The scale goes from one to fourteen. The smaller numbers are acids, the larger ones are bases, and the ones right around 7 are neutral.
Acids are substances that are higher up on the pH scale.
They run from 1 to 6. One is the strongest acids, and six is the weakest. Another way to test substances is with litmus paper, if they turn the paper red then they are acidic. In addition to this acids are known for having a sour taste. A caution, when working with substances in the lab, never stick anything in your mouth.