93 Y ou have probably heard the terms sour stomach, bitter herbs, buffered aspirin, heartburn, and acid rain. What do these terms describe? How are they related? To answer these questions, you need to take a close look at charged particles in solutions. You also need to define the terms acids, bases, and salts. Acids, bases, and salts are a related group of compounds. The structure and function of these compounds could not be defined until the nineteenth and early twentieth centuries. However, these substances have been recognized as a fundamental category of chemical compounds since ancient times. These substances have been primary factors in food pres- ervation and wine, cheese, and bread making throughout history, 6-1. Acids and bases also play a key role in digestion and many other bodily functions. Understanding how this classification of compounds func- tions can improve your baking skills. Knowledge about acids, bases, and salts can also help you maintain a safer, healthier food supply. Defining Acids and Bases Ions are charged particles or particles that have an imbalance of electrons and protons. Ions of opposite charges can form ionic bonds. These concepts provide a basis for learning about acids and bases and how they react in foods. Looking at water molecules can also help you better understand acids, bases, and salts. The Ionization of Water You will recall that the chemical formula for water is H2O. Two hydrogen atoms are bonded to one oxygen atom. However, a close analysis of water shows that pure water is not just a group of H2O molecules. At any given time, a small number of molecules in a volume of water are separating into ions and then recombining. This process of forming ions is called ionization. It is represented by the chemical equation below. The ability of the reaction to move in either direction is represented by a double-ended arrow. H2O H+ + OH– During the ionization process, a hydrogen atom breaks away from the water molecule. It leaves its electron with the oxygen atom. Remember that atoms prefer to have their outermost electron shell either full or empty. When the hydrogen atom gives its only electron to the OH group, it has an empty electron shell. The hydrogen atom becomes a positively charged hydrogen ion, which is represented by the symbol H+. However, scientists have found that hydrogen ions do not exist in water. A hydrogen ion has no electrons. Therefore, it is immediately drawn to bond with a water molecule with which it can share a pair of electrons. This forms a group of three hydrogen atoms and one oxygen atom. The group has a total of 11 protons but only 10 electrons, giving the group a positive charge. A hydrogen atom bonded to a water molecule is called a hydronium ion and is represented by the symbol H3O+. Key Terms ionization hydrogen ion hydronium ion hydroxide ion acid base salt neutral proton donor proton acceptor Bronsted-Lowry theory organic dye pH scale indicator titration endpoint equivalence point neutralization concentration Avogadro’s number mole molarity (M) chyme buffer botulism chemical leavening agent Goodshoot/Getty Images Plus 6-1 The production of these food products is based on principles of acid and base reactions. Copyright Goodheart-Willcox Co., Inc.