Notes on Procedure for Experiment No. 9
Your experimental setup consists of an electrolytic cell, in which water is reduced to generate
hydrogen gas and hydroxide ions at the cathode, and iodide ions are oxidized to elemental iodine at
the anode. The solution contains acetone, which reacts with the generated I2 under basic conditions to
produce iodoform (CHI3), a yellow solid that precipitates during the reaction.
The electrolytic cell will, for the most part, already be assembled for you. This supplement
contains instructions on how to operate the Vernier Constant Current System.
1. Ensure that your experimental apparatus has been set up as instructed. Your KI solution should be
prepared, added to the cell and stirring, the acetone added, and the inverted burette should already
be in place over the curved electrode.
2. Connect the LabQuest Mini to your computer using the USB cable.
3. Connect the Constant Current System to the data port on your LabQuest Mini.
4. Open LoggerPro in the menu at the top of the window and click Experiment, then Data
Collection. Under Sampling Rate, change samples/second to 1.
5. Connect the black clamp from your Constant Current System to the curved electrode. Connect the
red clamp to the other electrode.
6. When you are ready to begin, ensure that the voltage knob on the Constant Current System is
turned all the way up. Plug the DC adapter into an available electrical outlet and then to the
Constant Current System. Immediately after, press the Collect button at the top of the window in
LoggerPro.
7. Collect data until approximately 8.5 to 9 mL of hydrogen gas have been captured. When enough
gas has been produced, press the Stop button in LoggerPro and immediately unplug the power
source from the Vernier Constant Current System. Gas production will cease, but allow a few
minutes for the remaining hydrogen bubbles to float up to the surface of the water in the burette
before taking the volume reading. Proceed to the next step while you are waiting.
8. Press the Integrate button in LoggerPro. This will determine the area under the Current (in
amperes) vs. Time (in secs) curve, which is equal to the total charge (in coulombs) that was
transferred during the experiment. Use this value for the number of coulombs to calculate
Avogadro’s number and Faraday’s constant, as instructed in the lab manual.
9. Press the Statistics button in Logger Pro. This will give you the average current that passed
through the cell during the experiment. Multiply this average by the duration of current flow in
the experiment. Is this value close to the number given by the integration in Step 8?