• Conductivity Titration Directions
  
  For chemical and electrical reasons this activity should be done only as a teacher demonstration. Set up clean burets using a ring stand and buret clamp. Fill one buret with H2SO4 solution and the other with Ba(OH)2 solution. It is not necessary to fill each buret completely, but at least 40 mL of each solution should be present. Add 30-40 mL of H2SO4 from the buret to the 250-mL beaker.

  Add two to three drops of phenolphthalein indicator solution. Stir. (If available, a magnetic stirrer will be helpful.) Test the conductivity. (It is best to use a conductivity tester with a 60-W light bulb for this and to leave the electrodes immersed in the liquid.) Slowly add Ba(OH)2 solution from the other buret with stirring. Note the conductivity as the base solution is added. Stop the Ba(OH)2 addition as close as possible to the neutrality point. The light bulb should glow more dimly until it completely stops glowing. This is the neutrality point. The phenolphthalein color should become visible at the same point.

  After students have time to observe and record their observations, add additional Ba(OH)2 solution. The light bulb should begin to glow increasingly brightly and the phenolphthalein color should be come more pronounced. Ask students to propose explanations for the behavior of the conductivity light bulb.

Demonstration 5: pH and Environmental Gases

Dissolved gases often produce acidic or basic solutions.

• Materials
  
  5 Flasks, conical or round, 250-mL
  Universal indicator solution
  Gas source for CO2, NH3, and SO2
  Dry Ice, if available

• Safety
  
  Dry Ice can cause severe frost bite and should be handled with gloves or tongs. Other gas sources need to be handled carefully. Use the fume hood. Goggles should be worn.

• Directions
  
  Add 100 mL of distilled water to each flask. Add universal indicator solution to produce an intense color. Bubble each individual gas, one at a time, into the distilled water in the separate flasks. Add a piece of Dry Ice to the fourth flask. The fifth flask can be left with distilled water as a control. Have students observe and interpret the results.

Demonstration 6: pH Measurement

pH can be measured in several convenient ways.

• Materials
  
  Narrow and broad range pH paper
  pH pen or pH meter
  Solutions with various pH values

• Safety
  
  Become familiar with the operating instructions for the pH measuring device.

• Directions
  
  If a pH meter is available and used, show students not only how to use the meter but also how to calibrate the instrument at a pH close to the value to be measured. Adapt this demonstration to your needs and available pH measuring devices. Indicators may also be used to supplement the pH paper or meter observations.

	TABLE OF CONTENTS	TOPIC OVERVIEW	CONCEPT/SKILLS DEVELOPMENT	LINKS/CONNECTIONS	EXTENSIONS