Question

Procedure

1. Obtain a power supply and two cables that have alligator clips at one end. Also obtain two small pieces of insulated copper wire (approximately six inches, with a small amount of exposed wire at each end).

2. Completely Fill a 50 mL buret with 1 M sulfuric acid (to the top, not just the 0 mL mark).

3. Add 150 mL of 1 M sulfuric acid to a medium-sized beaker (250-400 mL).

4. Take a piece of insulated wire and insert one end in the buret (about 1-2 inches). Place a finger over the buret opening, holding the wire in place, then carefully invert the buret and set it into the solution in the beaker. Use a ring stand and clamp to hold the buret in place. [Note: the sulfuric acid you’re using has about the same acidity as household vinegar. Your finger will be fine; just rinse it off after completing this step]

5. Clip the other end of the insulated wire to the cable attached to the negative end of your power supply (keep the alligator clip out of the solution). This will serve as the cathode.

6. Take the other insulated wire and clip one end to the cable attached to the positive end of your power supply. Place the other end of the wire in the beaker. This will serve as the anode.

7. Turn on the power supply and adjust the voltage until hydrogen bubbles form in solution and the bubbles flow at reasonable rate (decrease voltage if the bubbling’s too fast, increase if too slow). Allow the reaction to continue until solution level in the buret is below the 50 mL mark then turn off the power.

8. Record the initial volume of the solution and turn on the power, noting the starting time of the reaction as well as the initial current being applied. Record the current in 5 mL intervals.

9. Turn off the power once 25 mL of hydrogen has been collected, noting the final volume of the solution.

10. Using a meter stick, measure the height of the solution remaining in the buret, starting from the surface of the solution in the beaker (not the buret opening).

11. Repeat this experiment two more times for a total of three trials. [Note: the exposed wire can dissolve in the acidic solution over time. After each trial, check your wire and use a razor or scissors to expose more wire, if needed.]

Questions

1. How would each of the follow errors affect your calculated value of Avogadro’s number (incorrectly high, low, or no effect)? Explain your answers.

a) The vapor pressure of water wasn’t factored into your calculations.

b) Part of the cathode was sticking out of the buret opening

c) 1.5 M sulfuric acid was used instead of 1 M.

d) The column height was not converted to units of mmHg

Answer 1