108 C H A P T E R 6 Review and Assess Summary When water ionizes, negatively charged hydroxide ions and positively charged hydronium ions are formed. Because these ions are always in balance in pure water, water is neutral. Acids have a surplus of hydronium ions, which gives them a positive charge. Acids are proton donors or electron acceptors. They turn litmus paper red and have a sour taste. Bases have a surplus of hydroxide ions, which gives them a negative charge. Bases are proton acceptors or electron donors. They turn litmus paper blue and have a bitter taste. When acids and bases are combined, they neutralize each other by forming water and a salt. The pH scale was developed to measure the concentration of hydronium ions in a solution. This scale is used to measure the relative strength and weakness of acids and bases. Through Avogadro’s work, the mole was developed as a way to accurately measure equal numbers of molecules of any substance. Molarity is the number of moles of any substance per liter of water. These measurements assist scientists in combining the proper amounts of acids and bases. Acids and bases play important roles in the body and in food products. The digestive process works because of carefully controlled pH levels in the body. The blood uses buffers to help maintain a constant pH. In the food industry, pH is related to the safe preservation of food. The development of chemical leavening agents and the production of baked goods also require an understanding of pH. Determining when to harvest many fruits is based on pH level, too. Check Your Understanding 1. List three atoms or groups of atoms found in pure water. 2. What is the difference between the Bronsted-Lowry theory and the theory of acids and bases proposed by Gilbert Newton Lewis? 3. Describe two common ways to identify acids and bases. 4. What does pH stand for? 5. Describe three ways to measure pH. 6. How many grams of acetic acid (CH 3 COOH) equal 1 mole? 7. Calculate the amount of acetic acid and distilled water needed to make 0.6 M CH 3 COOH. 8. Describe the importance of pH in digestion and give the pH of one acid and one base involved in digestion. 9. How do acids and salt help preserve food? 10. Explain how chemical leavening agents work. 11. Name three ingredients that can be added to a mixture when baking soda is the leavening agent used. 12. Describe how a double-acting baking powder works. 13. How does pH affect the quality of angel food cake? Copyright Goodheart-Willcox Co., Inc.