Electrochemical Writing

An iron nail can be used for writing in electrochemical system consisted of aluminum foil as second electrode besides the nail and filter paper soaked with electrolyte and phenolphthalein and potassium iodide.

Materials
One 9V battery or low-cost AC/DC adapter, insulated wire with crocodile clips, aluminum foil, filter paper, iron nail.
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Chemicals
Concentrated aqueous solution of sodium sulfate and phenolphthalein.

Experimental

• Place filter paper over the piece of the aluminum foil.
• Use the wire with crocodile clips to connect the iron nail and aluminum foil to the battery or another power supply (Fig. 1).
• Add few drops of sodium sulfate solution and phenolphthalein to the filter paper.
• Use the iron nail to write on the filter paper with a gentle touch on the part soaked with the solution.

Fig. 1. Set up

Fig. 2. Writing with different metals

Observation and Discussion

This experiment is actually an experiment of water electrolysis on paper. Try to write on the filter paper when iron nail is connected as a cathode and an anode. The iron nail will write only when it is cathode and the reason is the chemical reaction that takes place on cathode surface:

2H₂O + 2e^- → 4OH^- + 2H₂

In the presence of phenolphthalein the paper is getting red.
Potassium iodide solution can be added to the filter paper and in that case iron nail can write on both “modes” when it is anode and cathode.
This experiment is published with the results when it is performed with different electrolytes, different metals (Fig. 2) and different indicators: