Students will learn to write the half reactions that occur at each electrode during the electrolysis of water, performed in microscale using a 9V battery as a power source. In monitoring the pH at each electrode, studens will learn that H2 is accompanied by the formation of OH- ions and that H+ ions form as O2 is generated.
Before the Activity
Before beginning the activity, students should review the following terms-
anode, cathode, reduction, oxidation.
Students should have had previous exposure to balancing redox reactions.
The teacher needs to obtain one 9 V battery, 2 leads with alligator style clips at either end (available at Radio Shack), and a petri dish for each lab group. Prepare two electrodes for each group by breaking the eraser end off a number 2 pencil, then sharpening both ends of the pencil.
A solution of 1 M Na2SO4 should be prepared (142 g Na2SO4 per liter of solution).
Optional- Have a pipet of bromothymol blue (BTB) and/or phenolphthalein available to each lab group for additional exploration.
During the Activity
Hand out copies of the directions for the activity to each student.
After the Activity
Students may require assistance working through the half reactions. Assist as necessary.