overhead projector
edited by
DORISKOLB Bradley University Peoria, lL61625
Patriotic Electrolysis of Water Donald B. DuPre University of Louisville Louisville, KY 40292
A version of Shakhashiri's ( 1 )red, white, and blue electrolysis can be performed with a three-compartment, plastic Petri dish set up as shown in the figure. Loop a platinum wire bent into a 7'"shape over the edge of the dish with wire tips extending into ~ o m p a r t m e n t and s C. Another platinum wire is inserted in compartment B. (Use platin;m, not nickel-chromium wire, because the latter will produce a n interfering orange coloration during electrolvsis.) Salt bridees made of small ~ i e c e of s varn soaked in l " E(No8 ~ connect compartment B with compartments A and C. Fill each compartment with 1M KNOB.Add one drop of phenolphthalein to A and to B and one drop of thymolphthalein to C. If the solutions in compartments Aand C are not colorless, add a drop of vinegar. If the solution in com~artmentB is not red. add a d r o of ~ very dilute NaOH. hec colors of cornpartme& A, B, and C, thus start out a s white. red. and white, res~ectively.Attach the battery, terminal connected to the wire in COGwith the partment B. Immediate bubble activity is seen as the elec&olysis of water proceeds. The reaction a t the anode
produces hydroxide Ion, turning phenolphthalein in A red and thwnol~hthalein in C blue. After about 2 min. the rol" . ors of compartments A, B, and C, become red, white, and blue, respectively. (Some gentle stirring may be required for color uniformity) Reversing the battery attachments will restore the initial colors after about two additional minutes of electrolysis. In addition to the advantages of small quantities of chemicals and overhead projection, this version of the demonstration, with color reversal, may be completed within 5 min, as compared to the reported -35 min of class time required for the macmscopic version (1).
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2HzO(1)+Oz(g)+4H+(aq)+4e
produces hydrogen ion, turning phenolphthalein in compartment B colorless. The reaction a t the cathodes
70
Journal of Chemical Education
Patriotic electrolysis in a three-compartment dish. Platinum wire is used to make contact with solutions as shown. Salt bridges are made from yarn soaked in the electrolyte.
