Acids and bases are common substances found in many every day items, from fruit juices and soft drinks to soap. In this chapter, we will examine what the properties are of acids and bases, and learn about the chemical nature of these important compounds. You'll learn what pH is and how to calculate the pH of a solution. 15.1: Properties of Acids and Bases Acids and bases are distinct classes of compounds because of the properties of their aqueous solutions. 15.2: Common Acids and Their Uses Acids are very common in some of the foods that we eat. Citrus fruits such as oranges and lemons contain citric acid and ascorbic acid, which is better known as vitamin C. Carbonated sodas contain phosphoric acid. Vinegar contains acetic acid. Your own stomach utilizes hydrochloric acid to digest food. 15.3: Common Bases and Their Uses Bases are used in a wide variety of applications ranging from cleaning products to neutralizing stomach acid to production of pharmaceuticals. 15.4: Acids and Bases Defined Although the properties of acids and bases had been recognized for a long time, it was Svante Arrhenius in the 1880s who determined that the properties of acids were due to the presence of hydrogen ions, and the properties of bases were due to the presence of hydroxide ions. Later, Brønsted and Lowry broadened the definition by focusing on just hydrogen. They defined acids as species that donate hydrogens and bases as species that accept hydrogens in an acid-base reaction. 15.5: Strong and Weak Acids and Bases Acids and bases are classified as either strong or weak, based on their ionization in water. A strong acid or base is one which is completely ionized in an aqueous solution. A weak acid or base is one that ionizes only slightly in an aqueous solution. 15.6: Water as an Acid and as a Base Water is an interesting compound in many respects. Here, we will consider its ability to behave as both an acid and a base, resulting in the presence of both hydronium and hydroxide ions in any aqueous solution. The concentrations of the two ions are inversely proportional; so if the concentration of one is known, the other can be easily calculated. 15.7: An Introduction to pH pH is defined as the negative log of hydrogen ion concentration. It can be used to describe the relative acidity (or basicity) of a solution. Because it is based on a logarithmic scale, a change in pH of one pH unit corresponds to a ten-fold change in acidity. 15.8: pH and pOH Calculations pH and pOH are defined as the negative log of hydrogen ion concentration and hydroxide concentration, respectively. pOH is related to pH and can be easily calculated from pH. Knowledge of either one can be used to calculate either [H⁺] or [OH⁻]. 15.9: Reactions of Acids and Bases When an acid and a base are combined, water and a salt are the products. Salts are ionic compounds containing a positive ion other than H⁺ and a negative ion other than the hydroxide ion, OH⁻. Double displacement reactions of this type are called neutralization reactions. 15.10: For Future Use 15.11: Exercises Template:HideTOC Thumbnail Chapter 15: The pH scale. (Heinrich-Boll-Stiftung via Wikimedia Commons)