Suggestions for Other Laboratory Activities

These suggested activities are in outline format. Details for starred (*) activities are found in Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 3, (see References). Suggested demonstrations in the section that follows could also be used as laboratory activities. Caution: Use appropriate safety guidelines in performing these activities, since only brief procedural steps are described here.

1. Properties of Acids and Bases* Arrange eight beakers in two sets of four. Add 20 mL of each of the following to separate beakers: water, 2 M HCl, 2 M H2SO4, and 2 M HC2H3O2. Test each solution with litmus paper. Drop several magnesium turnings, Mg, to each beaker in one set of the four liquid samples. To each beaker in the second set of four, add 10 drops of litmus solution. Pour 25 mL of 6 M NaOH in each beaker. Add magnesium turnings to each beaker and compare the results with the previous set.

2. Define Acid, Base, and pH Operationally This can be accomplished with cabbage juice and/or universal indicator in household materials, hydrochloric acid, and sodium hydroxide at various concentrations, as outlined: Decant the purple liquid from canned red cabbage. Add 5 mL of the extracted juice to (1) 125 mL vinegar, (2) 125 mL household ammonia, (3) 1 teaspoon baking soda in 125 mL distilled water, (4) 125 mL colorless, carbonated beverage, (5) 5 mL of laundry detergent in 125 mL distilled water, (6) 125 mL of milk, (7) 125 mL of 0.1 M HCl, and (8) 125 mL of 0.1 M NaOH. Record the color of each mixture. Decide on the indicator color of red cabbage juice in acidic and basic solutions. Repeat with universal indicator.

3. Neutralization Titrate 20 mL 0.1 M HCl with 0.1 M NaOH using phenolphthalein as indicator. Repeat with 0.1 M H2SO4. Determine which titration requires more base. Explain results using balanced equation for neutralization of each acid by NaOH.

4. Titration of an Antacid* Weigh an antacid tablet accurately to nearest 0.01 g. Place tablet in an Erlenmeyer flask and add 100 mL of 0.15 M HCl to dissolve tablet. Add 5 drops of bromophenol blue indicator solution. If the indicator is blue, add HCl until it turns yellow. Record volume of HCl added. Titrate the sample with 0.1 M NaOH until the solution just turns blue. Calculate the mass of HCl solution consumed per gram of antacid tablet.

5. Distinction between Acid Strength and Acid Concentration* Separate beakers are filled with 40-mL samples of 0.1 M HCl, H2SO4, and HC2H3O2. Ten drops of phenolphthalein are added to each. The pH of each solution is determined with a pH meter or with pH test paper. 0.1 M NaOH is slowly added to each beaker of acid until the indicator just turns from colorless to pink. Compare the volumes of NaOH needed for each acid. Explain the results.

6. Strong vs. Weak Acids* Add 25 mL of 6 M, 1 M, 0.1 M HCl (strong acid); 6 M, 1 M, 0.1 M HC2H3O2 (weak acid) to separate beakers. Measure pH. Check conductivity of solutions and rank.Add Mg turnings to each beaker. Rank by reactivity.

7. Acid and Base Indicators* Mix 10 mL indicator solution with 50 mL colorless solutions having pH values ranging from 1 to 13. For indicator solutions that change color below pH 7 use bromophenol blue or methyl orange. For indicator solutions that change color near pH 7 use litmus or phenol red. For indicator solutions that change color above pH 7 use phenolphthalein. Compare colors in solutions of various pH.

8. pH of Familiar Products* Prepare standards for comparison by adding 10 drops of universal indicator to 50 mL of standard solutions representing pH values of 1, 3, 5, 7, 9, and 11. Add 10 drops of universal indicator to 50 mL of familiar products (fruit juice, vinegar, carbonated colorless beverage, milk, mouth wash, ammonia, bleach). Dissolve 5 mL (one teaspoon) of any of the following in 100 mL water: laundry detergent, hand soap, shampoo, drain cleaner, baking soda, antacid, aspirin. Add 10 drops of universal indicator to 25 mL of each. Compare colors for pH. Use a pH meter to determine accurately.

9. Concept of pH Serial dilution of an acid; measure pH with (1) pH paper, (2) pH meter, (3) various indicators; and/or (4) with assistance of a computer interface.

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