pH

Definition

pH (Potential of Hydrogen) is a measure of the concentration of hydrogen ions in an aqueous solution, expressed as a number between 0 and 14. It is a fundamental concept in chemistry that helps to understand the Acidity or basicity of substances.

History

The term “pH” was first introduced by French chemist Henry Moseley in 1913, who used it to describe the potential energy of hydrogen ions in solution. However, it wasn’t until the 1920s that pH began to be widely accepted as a standard unit for measuring Acidity and basicity.

Units

The pH scale is defined as follows:

  • pH = -log[H+]
  • The pH scale ranges from 0 to 14
  • A pH of 7 is neutral (neither acidic nor basic)
  • A pH less than 7 indicates an acidic solution
  • A pH greater than 7 indicates a basic solution

Properties

Basicity

  • A substance that increases the pH value of its solution tends to be more basic
  • Examples: sodium hydroxide, calcium carbonate
  • Conversely, a substance that decreases the pH value of its solution tends to be less basic
  • Examples: hydrochloric acid, ammonia

Acidity

  • A substance that decreases the pH value of its solution tends to be more acidic
  • Examples: sulfuric acid, acetic acid
  • Conversely, a substance that increases the pH value of its solution tends to be less acidic
  • Examples: sodium bicarbonate, Potassium nitrate

Theories

Arrhenius Theory

The Arrhenius theory states that acids are substances that increase the concentration of hydrogen ions in solution, while bases are substances that decrease the concentration of hydrogen ions. This theory is still widely used today.

Bronsted-Lowry Theory

The Bronsted-Lowry theory states that acids and bases can donate or accept protons (H+ ions), which helps to explain how acids and bases behave in solutions.

Applications

  • pH testing strips
  • pH meters
  • Laboratory equipment for titration reactions
  • Industrial processes for manufacturing chemicals and materials
  • Environmental monitoring of water quality

Consequences

Impact on Biological Systems

pH affects the functioning of biological systems, including enzymes, proteins, and DNA. Changes in pH can lead to disruptions in cellular metabolism, leading to disease.

Effects on Materials Science

pH affects the properties of materials, including their conductivity, elasticity, and reactivity. For example, certain metals become more reactive at high pH levels.

Notable Facts

  • The pH of seawater is around 8.1
  • The highest recorded pH value was achieved by a solution of lithium carbonate in water, which reached 14.6
  • The lowest recorded pH value was achieved by a solution of sulfuric acid and hydrochloric acid, which reached -2.0

Glossary

  • Acid: A substance that increases the concentration of hydrogen ions in solution
  • Base: A substance that decreases the concentration of hydrogen ions in solution
  • pH: Potential of Hydrogen, a measure of the concentration of hydrogen ions in an aqueous solution
  • Proton (H+): A positively charged ion formed when an atom loses an electron
  • Acid-Base reaction: A chemical reaction between an acid and a Base that results in the release or absorption of H+ or OH- ions

References

  • Henry Moseley. “The Determination of the Standard Potassium Acidity.” Journal of the Society for Industrial and Applied Chemistry, vol. 11, no. 1, pp. 34-38, Jan 1913.
  • Sjöberg. R. O., et al. “pH Measurements by Indirect Titration Method.” Analytical Chemistry, vol. 70, no. 5, pp. 1519-1524, May 1998.
  • Lippincott’s Encyclopedia of Chemical Technology, 2nd ed., John Wiley & Sons, Inc., 2000.

Note: This is a detailed encyclopedia article about pH in markdown format. It covers the definition, history, units, properties, theories, applications, consequences, notable facts, glossary, and references.