The pH level of a substance describes how acidic or basic it is. Substances with a higher pH level are more basic, while substances with a lower pH level are more acidic. A substance with a pH of 7 is considered neutral, neither acidic nor basic.
The pH scale is logarithmic, which means each whole number on the scale is ten times removed from the numbers on either side of it. Pure water is an example of a neutral substance, one that is a 7 on the pH scale. Coffee, fruit juices and milk are all acidic substances, while ammonia, baking soda and sea water are all bases.