EGEE 102
Energy Conservation and Environmental Protection

pH Scale

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Acid rain is measured using a pH scale.

pH is a measure of hydrogen ion concentration, which is measured as a negative logarithm. In other words, acids produce hydrogen ions and alkalis produce hydroxyl ions, so pH is the power of a solution to yield hydrogen ions [H+].

The pH scale ranges from 0 to 14 and indicates how acidic or basic a substance is.

  • A pH of 7 is neutral.
  • A pH less than 7 is acidic.
  • A pH greater than 7 is basic.

The lower a substance's pH, the more acidic it is. Each whole pH value below 7 (the neutral point) is ten times more acidic than the next higher value.

  • For example, a pH of 4 is ten times more acidic than a pH of 5 and 100 times (10 times 10) more acidic than a pH of 6.

The higher a substance’s pH, the more basic or alkaline it is.

  • Each whole pH value above 7 is ten times more alkaline (another way to say basic) than the next lower whole value.
  • For example, a pH of 10 is ten times more alkaline than a pH of 9.
The pH Scale ranges from zero to fourteen - (Lemons are 2.2 to 3.0, apples are 2.9 to 3.3, milk is 6.4 to 7.6, and ammonia is 11 to 12.)
The pH Scale