Introduction
Electrical current is applied to water containing Na2SO4as an electrolyte. The water is converted into gaseous H2and O2at the electrodes.
ANODE HALF REACTION: 2H2O—>4H++ O2+ 4e-
CATHODE HALF REACTION: 4H2O + 4e-—>2H2+ 4OH-
OVERALL REACTION: 2H2O—>2H2+ O2
To Conduct Demonstration
- Attach one alligator clip from the battery pack to each electrode.
- Oxygen and H+are formed at the anode (oxidation), and the indicator turns red. Hydrogen and OH-are formed at the cathode (reduction), and the indicator turns blue. After a few minutes, a relative volume ratio of 2 H2:1 O2should be visible.
Demo Time: ~2 – 5 minutes
NOTES:
- It takes up to 5 minutes for the reaction to show well.
- Put a paper towel under to open end of the apparatus to catch the overflow.
- The solution can be used over again, but must be returned to the green color using 0.01M or 0.1 M NaOH or .01 M or 0.1M H2SO4. It should only take a few drops.(If it takes a lot, remake the Na2SO4solution).
- It is not necessary to make up a universal indicator. A commercially prepared preparation is fine.
Safety and Disposal
The electrolysis apparatus is somewhat fragile, and care should be taken in packing and transporting it.
REFERENCE:
C.L. Borgford and L.R. Summerlin,Chemical Activities, Teacher Edition,1988.