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Health & Safety
Wear eye protection throughout.
A. Pour the 0.2 M sodium sulfate solution into the 100 ml bottle so it reaches the very top.
B. Have a beaker handy to collect the overspill as the bung containing the electrodes is inserted into the neck of the bottle. The overflow rises up the delivery tube and empties into the beaker.
C. Connect the copper wires to the low-voltage supply (6-8 volts is a suitable setting) and pass current until no more solution is pushed out of the bottle into the beaker. All this can be prepared earlier and the current turned off.
D. Place the crucible filled with 50% liquid detergent solution on the laboratory jack or wooden blocks so that gases from the bottle will bubble through. Switch on the current to collect bubbles of gas.
E. Switch off the current, lift the bottle so that the tube is clear of the crucible and move the crucible closer to an ignited Bunsen burner.
F. Light a splint with the Bunsen burner flame and apply to the bubbles on the top of the crucible.
- Wear eye protection.
- The Bunsen burner required for this demonstration should be at least 1 m from the bottle.
- The first gas sample may not explode with a loud crack as air might be present, so repeat the procedure.
- The glass tubing should be flush with the bottom of the bung.
- The electrolyte is 0.2 M sodium sulfate solution rather than sulfuric acid. More advanced students will appreciate that water molecules are being oxidised and reduced at the electrodes to form oxygen and hydrogen.
- This method uses nickel electrodes in place of platinum which are expensive and difficult to solder. However, the nickel anode does oxidise during the process if the electrolysis cell is left on for long periods. The solution becomes green and nickel(II) hydroxide precipitates out.
Disposal: All solutions can be poured down the foul-water drain.
This experiment has been reproduced from CLEAPSS®, L195 Safer chemicals, safer reactions p.26 with permission from CLEAPSS®