Definition of the pH Scale
The pH scale is a logarithmic measure of the hydrogen ion concentration in a solution, used to indicate its acidity or basicity. Defined as pH = -log10[H+], where [H+] is the molar concentration of hydrogen ions, the scale ranges from 0 to 14. Values below 7 indicate acidity, 7 is neutral, and above 7 indicates alkalinity or basicity.
Key Principles of the pH Scale
The scale is logarithmic, meaning each unit represents a tenfold change in hydrogen ion concentration. For example, a pH of 3 is ten times more acidic than a pH of 4. It applies primarily to aqueous solutions and is temperature-dependent, though standard measurements assume 25°C. Indicators like litmus paper or pH meters are used to determine pH values accurately.
Practical Examples of pH Values
Common substances illustrate the scale: hydrochloric acid in the stomach has a pH around 2, making it highly acidic; pure water is neutral at pH 7; and sodium hydroxide, a strong base, has a pH of 14. Seawater typically measures about 8.1, slightly basic, while coffee ranges from 4.9 to 5.5, mildly acidic.
Importance and Applications of the pH Scale
The pH scale is crucial in chemistry for controlling reactions, such as in industrial processes like food preservation or wastewater treatment. In biology, it maintains homeostasis, like blood pH at 7.4 for enzyme function. Environmental monitoring uses it to assess soil acidity for agriculture or ocean acidification due to CO2 absorption.