Quick Lab
Identifying a Chemical Change
Materials
3 test tubes; test-tube rack; glass-marking pencil;
3 10-mL graduated cylinders; solutions of copper sulfate, calcium chloride, and sodium chloride
Procedure 
Construct a data table with columns labeled Test Tube, Contents, and Observations.
Label the test tubes A, B, and C.
Pour 5 mL of copper sulfate solution into test tube A. Pour 5 mL of calcium chloride solution into test tube B. Pour 5 mL of sodium chloride solution into test tube C. CAUTION Do not allow the solutions to touch your skin. They may cause irritation.
Add 5 mL of calcium chloride solution to test tube A. Add 5 mL of sodium chloride solution to test tube B. Add 5 mL of copper sulfate solution to test tube C.
Examine the test tubes for evidence of a chemical change. Record your observations.
Pour the contents of the test tubes into the sink. Rinse out the test tubes and flush the contents down the drain. CAUTION Wash your hands thoroughly with soap or detergent before leaving the laboratory.
Analyze and Conclude
Inferring In which test tube(s) did a chemical change occur? Explain your answer.
Evaluating Can yo be sure that a chemical change occurred? Explain your answer.
Recognizing Chemical Changes
Figure 18 shows what happens to banana peels as bananas ripen. The color change in a banana peel is caused by chemical changes that are taking place in the cells of the banana. A chemical change occurs when a substance reacts and forms one or more new substances. Chemical changes occur when a cake bakes in an oven, leaves on trees change color, and food is digested in your stomach.
How can yo recognize a chemical change? Yo have to look for clues. For example, when food spoils, it often gives off an unpleasant odor. 
Three common types of evidence for a chemical change are a change in color, the production of a gas, and the formation of a precipitate.
Figure 18 As a banana ripens, chemical changes cause the peel to change color from green to yellow. In a banana that is overly ripe, different chemical changes cause the peel to turn brown.
Observing Based on your experience, what other properties of a banana change as it ripens?
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