Students should also be asked occasionally to give examples of acid-base phenomena that were not observed in laboratory activity to see whether they can extend the concepts.

Answers to Implications and Applications

Part I

1. Use one of the three indicators to test for an acid or a base.
   
2. Bromthymol blue changes to yellow in an acid solution or in a solution of pH less than 6 (see Figure 2).
   
3. In solutions of different concentrations of acids or bases, the universal indicator has different colors.
   
4. All acids seem to have H⁺(aq), and all bases seem to have OH^-(aq).
   

Part III

1. Many household products display acidic or basic properties.
   
2. Most commercial cleansing products are basic. Most fruits tend to be acidic.
   

Possible Extension

A good group activity is to conduct an acid-base scavenger hunt. Send students out with a well plate or test tubes and universal indicator to identify five additional acids and five additional bases in their everyday environment. They can complete this as a take-home activity, if you choose.

Assessing Laboratory Learning

1. Lab Practical. Give individuals or groups of students one or more unknowns. Have students categorize the samples as acidic and/or basic, indicating which solution(s) from Part II had comparable pH values.

2. Demonstration Exam. Same as lab practical, but you demonstrate the tests. Carry out a series of reactions, describing at each step what you are adding and allowing students to observe the results. Then have students categorize and/or identify the pH of the unknown substance.

3. Written Exam. Here are some possible items:
   
   a. Three identical samples of a clear, colorless liquid are tested: Magnesium is added to Sample 1; no reaction is observed. To Sample 2 is added calcium nitrate; the liquid turns cloudy. Universal indicator is added to Sample 3; the indicator turns bluish-purple. Is the unknown liquid acidic, basic, or neutral? [Basic]

   b. Universal indicator can be made to turn various colors, depending with what it is mixed. What property determines the color shown by universal indicator? [Whether the substance being tested is an acid or a base (see Figure 2).]

   c. In what ways are some materials commonly available in grocery stores similar to materials commonly used in a chemistry laboratory? [Some materials are acids (vinegar, 7-Up, orange juice); some are bases (baking soda, milk of magnesia).]

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