Since the beginnings of experimental chemistry, scientists have recognized acids or bases by their characteristic properties. Acids taste sour (e.g., citric acid in lemon juice) and cause certain dyes to change color (e.g., litmus paper turns red when in contact with acidic substances). The word acid comes from the Latin word acidus, which means sour or pungent.
Bases, on the other hand, taste bitter and are slippery to the touch (soap is a good example). The word base comes from the Latin basis, foundation or support. When bases are added to acids, they reduce or lower the amount of acid. In fact, when acids and bases are mixed in certain proportions, their characteristic properties disappear completely.
Ideas about acids and bases are commonplace in everyday life. The environmental problem of acid rain is a frequent topic in different parts of the world. Television commercials mention pH in connection with a wide variety of products such as antacids, deodorants and shampoos.
Many organic acids occur in the plant kingdom. Molecular models show Ascorbic Acid, also known as Vitamin C (C6H8O6), Citric Acid (C6H8O7) (found in Lemons, Oranges and Tomatoes) and Oxalic Acid (H2C2O4) (Spinach). Acids and Bases are important in numerous chemical processes going on around us, from industrial to biological processes, from reactions in the laboratory to those in our environment. For example:
- The time required for an object immersed in water to corrode.
- The capacity of an aquatic environment for the survival of fish and plant life.
- The fate of pollutants washed from the air by rain.
- The rate of life-sustaining reactions depends critically on the acidity or basicity of the solutions.
In this unit we will study modern acid-base theories, the pH scale, the factors that relate to the strength of acids and bases, calculation of ion concentrations in acid and base solutions, among others.