Colors around the Cathode

Two Petri dishes, insulated copper wire, banana plugs, alligator clips, glass plate, polished nickel-plated sheet iron (about 10 x 15 cm) as support, source of DC current (lOV), hair dryer, spatula, measuring cylinder, dropping pipettes, safety glasses, protective gloves. 

5 % sodium chloride solution, ethanol, 1 % alcoholic solutions of bromothy-mol blue and phenolphthalein, filter paper. 

If one intends to write or draw electrolytically, the polished nickel plated sheet iron is placed underneath the filter paper and connected to the positive 

During the electrolysis of an aqueous sodium chloride solution elemental chlorine is formed at the anode from the chloride ions, while at the cathode H30 ions are reduced to molecular hydrogen. The area around the cathode contains an aqueous solution of the Na and OH ions, which determine its basicity and cause the indicator to change color. It is thus possible to generate different color effects in the area around the cathode by changing the indicator used. 

Solutions which are no longer required can be poured down the drain. 

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