PURPOSE: To show that pure water is not conducting, but a solution of an electrolyte is conducting.

DESCRIPTION: A 110 VAC lead is connected to a series arrangement of a light bulb and two parallel plates. Shorting the plates will light the bulb. Inserting the plates into distilled water does not light the bulb (photo at right). Inserting the plates into tap water lights the bulb dimly (photograph in center) and inserting the plates into salt water lights the bulb fully (photograph at left). An electrolyte solution allows passage of electric current. The beaker at the right in the photographs contains clean water to rinse the electrodes.

SUGGESTIONS: See Question of the Week #191 for suggestions on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 5D30.10)

EQUIPMENT: Bottles of distilled water, tap water, and salt water, series 110 VAC circuit with light bulb and two plates.

SETUP TIME: None.