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26c. Analysis of water by adding red cabbage juice ("Micro-Hofmann")

Material: 2 Liquemin bottles full of sodium sulfate solution with red cabbage juice, small plastic honey packing,  2 sterile hypodermic needles extracted from an 1-mL insulin syringe, 9-Volt battery, electric wire with crocodile clips, plastic pipette, goggles, candle, matches, white film canister.
Experiment:
1. Pierce a small plastic honey  packing with two hypodermic needles extracted from an insulin syringe.
    Choose a distance between the needles to have space for two bottles to be put over them.
2. Cover the bottom of the packing with sodium sulfate solution + red cabbage juice.
3. Make an electric connection between the battery an the lower ends of the needles.
4. Carefully turn the bottles full of solution and put each of them over one of the needles.
5. Wait until the bottle connected with the negative terminal of the battery is full of gas.
6. Ask your teacher to demonstrate a test for pure hydrogen ("negative oxyhydrogen test").
7. In the other bottle a test for pure oxygen is made ("glowing paper test").
8. Right photo: Transfer a big drop of blue sodium sulfate solution on the bottom of a white fil canister.
    Close an electric circuit by dipping the two needles into the solution.
Evaluation. The following conclusion can be drawn from the observations:
The analysis of water results in hydrogen and an alkaline solution (container with negative electrode) and in oxygen and an acidic solution (container with positive electrode)  JUSTIFY THIS CONCLUSION MAKING USE OF THE OBSERVATIONS.