Major Chemical Concepts
This laboratory activity is designed to develop operational definitions for acids, bases, and pH. It should be used as an introduction to acids and bases before students learn verbal or mathematical definitions of important terms. Conceptual definitions can be developed, if desired, during the post-lab discussion.
Expected Student Background
Students should be able to calculate the new concentrations of solutions after they are diluted and be familiar with standard laboratory procedures. Students should also be familiar with the electrical conductivity of ionic solutions.
Appropriate for any basic or general student.
This laboratory activity can be completed in two class periods. However, it can occupy over three periods if you use extended discussion to isolate, define, and solidify concept acquisition.
Read the Safety Considerations section in the student materials. In addition, be sure that students treat commercial products as potentially hazardous; some are caustic or can lead to dangerous reaction products if mixed together. For example, if Vanish(TM) and household bleach are mixed together, poisonous chlorine gas is produced.
Materials (FOR 24 STUDENTS WORKING IN PAIRS)
Part I Materials
0.1 M Hydrochloric acid, HCl (2 mL conc HCl, dilute to 250 mL)
0.1 M Sodium hydroxide, NaOH (1 g NaOH, dilute to 250 mL)
0.1 M Sulfuric acid, H2SO4 (See Advance Preparation)
0.1 M Nitric acid, HNO3 (1.5 mL conc HNO3, dilute to 250 mL)
0.1 M Potassium hydroxide, KOH (1.5 g KOH, dilute to 250 mL)
Saturated barium hydroxide solution, Ba(OH)2 (15 g Ba(OH)2, dilute to 250 mL)
1.0 M Calcium nitrate, Ca(NO3)2 (8 g Ca(NO3)2 dilute to 50 mL)
Distilled (not deionized) water
Magnesium ribbon, Mg, 10-cm length
Bromthymol blue indicator (See Advance Preparation)
Phenolphthalein indicator (See Advance Preparation)
12 Conductivity testers
12 Well-plates or 504 small test tubes and racks
12 small 25-cm2 pieces of fine-grade sandpaper or steel wool
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