Question

Demonstration

Electrolysis of molten zinc chloride

Safety

• This demonstration should be performed in a fume hood.

• Wear safety glasses.

• Follow correct disposal procedures.

Materials

• Large porcelain crucible

• $15 g$ of zinc chloride

• Tripod stand and clay-pipe triangle

• Bunsen burner

• Retort stand and clamp

• 2 carbon electrodes

• Connecting wires and crocodile clips

• 1 light bulb

• DC power supply $(6 V)$

Method
1. Set up the apparatus as shown in the diagram.

2. Light the Bunsen burner, open the gas sleeve to produce a blue roaring flame and heat continuously until a molten solution of zinc chloride is produced.
What did you observe about the light bulb as the zinc chloride solid began to melt and become molten? Support your answer with scientific reasoning.

Accepted Answer

Initially when the zinc chloride is a solid, the light-bulb is not lit. As the zinc chloride begins to melt, the light bulb begins to flicker and eventually is fully lit. As solid ionic compounds, the ions in zinc chloride are unable to move between the electrodes to complete the circuit and therefore no electrons will flow in the external circuit. When zinc chloride is molten, the redox reactions at the anode and cathode will proceed, ions in the molten electrolyte can pass between the electrodes, electrodes will begin to flow from the anode to the cathode and the bulb will be lit.

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