Chapter 6.8 Acidity 1 PDF

Measuring the Acidity 6.8 of Solutions Have you ever wondered what makes lemon juice sour (Figure 1)? Lemon juice is a solution that contains dissolved compounds. Scientists...

Measuring the Acidity 6.8 of Solutions Have you ever wondered what makes lemon juice sour (Figure 1)? Lemon juice is a solution that contains dissolved compounds. Scientists classify some compounds by the properties of the solutions they form. Figure 1 Lemon juice has a sour taste. LEARNING TIP Acids are compounds that form solutions with the following Check your understanding properties: of the properties of acids and bases. Work with a have a sour taste partner and take turns react with (corrode) metals describing the properties. can cause serious burns on skin Many acidic solutions, such as lemon juice and vinegar, are harmless. They can be used to give foods a tangy flavour. Other acidic solutions are extremely dangerous. Hydrochloric acid, for example, is used to etch concrete and would make holes in your skin or clothing. Bases are compounds that form solutions with the following properties: have a bitter taste feel slippery react with (break down) fats and oils can cause serious burns on skin Some basic solutions are harmless. You can drink a solution of baking soda and water to calm an upset stomach. Other basic solutions, such as drain cleaner, should be used with extreme care. They should never be allowed even to touch your skin. 160 Unit B Chemistry NEL  You often use the properties of acidic and basic solutions in your daily life. Some common acids and bases are shown in Figure 2. LEARNING TIP Make connections between what you are learning about the properties of acids and bases in this section and what you already knew about the products in Figure 2. Ask yourself, “Did I already know these products had these properties?” Figure 2 Common acids (left) and bases (right) Identifying Acids and Bases Because many acids and bases are not safe to taste, scientists use other properties to identify them. One property that is safe to use is their effect on a dye called litmus [LIHT-muhs]. Acidic solutions turn blue litmus paper red. Basic solutions turn red litmus paper blue. Litmus is called an indicator because it indicates whether a solution is acidic or basic (Figure 3). Figure 3 Blue litmus paper turns red in an acidic solution (left). Red litmus paper turns blue in a basic solution (right). NEL 6.8 Measuring the Acidity of Solutions 161  Scientists measure acidity on the pH scale—a scale of numbers running from 0 to 14 (Figure 4). If a compound is neither an acid nor a base, it is neutral and has a pH of 7.0. Pure water, for example, is neutral. Acidic solutions have pH values that are below 7. The more acidic a solution, the lower its pH value is. A solution with a pH between 0 and 3 is very acidic. Basic solutions have pH values that are above 7. The more basic a solution, the higher its pH value is. Very basic solutions, such as drain cleaners, have pH values that are close to 14. neutral more acidic more basic 7.0 vinegar normal milk human ammonia rain 6.6 blood drain 2.2 11.1 5.6 7.4 ocean cleaner water 13.8 battery acid apples 8.3 0.5 3.0 lemon juice tomatoes baking soda milk of magnesia 2.0 4.2 8.2 10.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Figure 4 The pH values of some common substances CHECK YOUR UNDERSTANDING 1. Make a Venn diagram to compare acids and bases. Include at least two examples for each. 2. When might you need to know whether a solution is acidic or basic? 3. Dishwasher detergent, oven cleaner, and drain cleaner are all basic solutions with high pH values. What property of basic solutions makes these products useful? 162 Unit B Chemistry NEL