Materials: Hofmann apparatus with integrated platinum electrodes, stand, 30 Volt DC power supply (alternative power supplies)
Left: 1.  Boil extract a handfull of red cabbage juiceInsert steel electrodes from paper clips into two rubber stoppers.
2. Close a Hofmann Apparatus by these stoppers. 3. Fill the three tubes of the Hofmann with a conc. solution of table salt in red cabbage juice.
4. Connect its electrodes with a 30-Volt power source.
Observations: Gas bubbles at both electrodes (double volume at the negative electrode).Cathode :  The colour of the red cabbage juice changes from blue to green.
Anode:     The colour of the red cabbage juice changes from blue to red.
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.