Information on pH Levels

Orange juice is acidic.

pH levels refer to the concentration of hydrogen ions in a solution. Since hydrogen ions have a positive charge, they affect other molecules in a solution. Scientists measure hydrogen ion concentration with the pH scale, which ranges from zero to 14. Solutions that have a pH from zero to seven are considered acidic while solutions with a pH from seven to 14 are considered basic or alkaline. Solutions with a pH of exactly seven are considered neutral. Pure distilled water is a neutral solution.

History

Amateur chemist Robert Boyle separated substances into acidic and basic categories in the seventeenth century. Nineteenth-century Swedish scientist Svante Arrhenius refined Boyle's definitions and analyzed the process of neutralization. The pH scale scientists use today was developed in 1909 by the Danish biochemist Sören Sörensen. Danish scientist Johannes Brønsted and English scientist Thomas Lowry both further developed Arrhenius' theory in papers they published in 1923.

Calculating pH Levels

The formula for pH is logarithmic, so each pH level is ten times more acidic or basic than the number above or below it. For example, a solution with a pH of three, such as orange juice, is ten times more acidic than a solution with a pH of four, like tomato juice. Similarly, a solution with a pH of 11, like ammonia, is ten times more basic than a solution with a pH of ten, like milk of magnesia.

Significance

Since pH is logarithmic, small differences in pH can have a significant impact. For example, acid rain generally has a pH of 4.0 to 4.4, according to the U.S. Environmental Protection Agency (EPA). This means that acid rain is more than ten times more acidic than clean rain, which generally has a pH around 5.6.

Measuring pH Levels

Litmus strips, a special type of paper, change color in solutions to indicate pH. In alkaline solutions, litmus paper turns blue. It turns red when placed in acidic solutions.

Bases

Basic or alkaline solutions contain fewer hydrogen ions than acidic or neutral solutions. Instead, they contain hydroxide ions. Bases usually taste bitter and feel slippery. Common basic solutions include sea water (pH of eight), baking soda (pH of nine), soapy water (pH of 12), and liquid drain cleaner (pH of 14).

Acids

Acidic solutions contain more hydrogen ions than alkaline or neutral solutions. Acids usually have a sour taste. They also react with metals and can burn your skin. Common acidic solutions include vinegar (pH of two), soda (pH of three), and black coffee (pH of five).

Neutralization

Neutralization occurs when acids and bases with equal amounts of hydrogen and hydroxide ions are mixed. Neutralization reactions produce salt and water.

References

• EPA: pH Scale
• Vision Learning: Acids and Bases
• University of Illinois, Urbana-Champaign: Acids Bases and pH Scale
• Elmhurst College: pH Scale