Experiment #1: Battery-powered water-splitting
Purpose: The purpose of this experiment is two-fold: 1) to demonstrate our ability to split H2O into its elemental components - H2 and O2 - using an electrochemical cell, and 2) to capture and volumetrically determine if the amount of H2 and O2 gas (captured separately) evolved during the reaction is consistent with the overall stoichiometry of the reaction: 2 H2O --> 2 H2 + O2.
Hypothesis: The volume of H2 produced should be TWICE that of the volume of O2 produced, in accordance with the balanced chemical equation shown above.
Materials and Supplies:
Special Materials
1) As designed here, this experiment requires a lab-built amperostat that can control and display the amount of electric current that is used during the reaction.
2) The experiment also requires an assembly of twin electrodes that consists of nickel wire (0.02-0.2 mm diameter) encapsulated inside two graduated plastic test tubes (5-25 mL, 1 mL graduations).
Common Materials
1) One beaker (250-500 mL), sodium sulfate (Na2SO4), deionized/distilled H2O.
2) Electrical leads (alligator clips), batteries (2 x 6V heavy duty, for longest life).
Procedure:
Preparation of the Electrochemical Water-Splitting Cell
1) Fill the beaker about 2/3 full with deionized/distilled H2O, and dissolve 1 g of Na2SO4 (sodium sulfate).
2) Fill the twin nickel electrode assembly to the top with the H2O/Na2SO4 solution.
3) This part (steps 3 and 4) is a bit tricky: hold the beaker and twin-electrode/tube assembly at about 45o angle to each other, brim to brim.
4) Quickly submerge the filled electrode/tubes in the beaker H2O solution, retaining the vast majority of the liquid within the tubes. For example, using a 15 mL test tube typically 10-14 mL of liquid should be retained.
5) Hook up the electro-station to each nickel wire electrode using the alligator clips. Be sure at this time that the power switch is turned to the "OFF" position, and dial the current control knob to the "MINIMUM" setting.
Performing the Experiment
The experiment can be performed in two different ways: using either time or applied current as the dependent variable. Both are described below
A) Time-dependent Electrolysis
1) Inside the electrode/tube assembly, write down the volume reading that indicates the level of water in both test tubes.
2) Turn the power switch to the "ON" position, and adjust the current knob such that the display needle reads approximately 100 mA. Let the reaction run for 5 min.
3) During the reaction, closely observe what happens at the tips of the electrodes and make notes as to your observations.
4) At the end of 5 min, make note of the new volume in your lab notebook.
5) Next, perform the electrolysis experiment for 10, 15 and 20 min. Return to Step 2 of the Preparation of Experiment Section above to set up the experiment again.
B) Current-dependent Electrolysis
1) Inside the electrode/tube assembly, write down the volume reading that indicates the level of water in both test tubes.
2) Turn the power switch to the "ON" position, and adjust
the current knob such that the display needle reads approximately 50
mA. Let the reaction run for 5 min.
3) During the reaction, closely observe what happens at
the tips of the electrodes and make notes as to your observations.
4) At the end of 5 min, make note of the new volume in your lab notebook.
5) Next, perform the electrolysis experiment tuning the aperometer to 100, 150 and 200 mA. Return to Step 2 of the Preparation of Experiment Section above to set up the experiment again.
Data and Results:
