. .  Electrolysis of sodium sulfate solution in a 5-mL-bottle and in a blister Take  safety precautions concerned with electricity. Work on a tray Left:  Puncture the stopper of a Liquemin bottle by two hypodermic needles, blunt their tips. Fill the bottle with conc. sodium sulfate solution and close it by the stopper.
Connect the needles with a 9-Volt battery. Place the bottle upwards down on a second bottle. Observations:
* Gas bubbles appear at both electrodes, more bubbles can be seen at the cathode. The liquid is pressed out of the upper bottle through the blunted needles.
* The gas explodes when lit in a candle.
Middle: Build an electric circuit by a 9-Volt battery, two insulated wires with crocodile clips, a light emitting diode (LED) and a blunted needle both dipped into a blister with sodium sulfate solution + red cabbage indicator.
Observations :
Right: Gas bubbles appear at both electrodes, more bubbles can be seen at the cathode (-). The colour of the indicator around the cathode changes to green/blue.
Explanation:    Red: 4 H₂O(l)  + 4 e^- --> 2 H₂(g) + 4 OH^-(aq)
                  Ox:          2 H ₂O(l)  --> O₂(g) + 4 H⁺(aq) + 4 e ^-
                           Redox:           6 H ₂O(l)  --> 2 H₂ (g) +  O₂ (g)  + 4 OH^-(aq) + 4 H⁺(aq)
Colour change : The different colours of the red cabbage juice result from acid base reactions of coloured compounds called anthocyans (anthos = flower, kyanos = blue). Their cations "are especially interesting because they behave much like the pH indicator..." (S.S.Zumdahl, Chemistry) phenolphthalein.

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