Definition of pH
pH is a numerical scale used to specify the acidity or basicity of an aqueous solution. It is defined as the negative logarithm of the hydrogen ion concentration: pH = -log₁₀[H⁺]. Solutions with pH less than 7 are acidic, pH greater than 7 are basic (alkaline), and pH of 7 indicates neutrality at 25°C, as in pure water.
The pH Scale and Key Principles
The pH scale ranges from 0 to 14, where each unit represents a tenfold change in hydrogen ion concentration. Acidic solutions have higher [H⁺] and lower pH values, while basic solutions have lower [H⁺] and higher pH values. This logarithmic scale allows for concise expression of concentration differences spanning many orders of magnitude.
Methods of Measuring pH
pH is commonly measured using a pH meter, which employs a glass electrode sensitive to hydrogen ions and a reference electrode to generate a voltage proportional to pH. Alternative methods include pH indicators, such as litmus paper or universal indicator solutions, which change color based on pH ranges, and titration with standard acids or bases for precise determination.
Practical Applications and Importance
pH measurement is essential in fields like chemistry, biology, and environmental science. For example, maintaining blood pH between 7.35 and 7.45 is critical for human health, while soil pH testing guides agriculture to optimize nutrient availability. Accurate pH control prevents corrosion in industry and monitors water quality in ecosystems.