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Me16b Water electrolysis 2: Pipette with hypodermic needles for analysis and volumetric re-synthesis
Upgrading this apparatus in TWO pipettes

In an ealier experiment you have ignited the gas mixture obtained from water electrolysis to measure volumes. By changing to a plastic pipette apparatus you can do analysis and volumetric synthesis in the same container.
What you need: Plastic pipette with 4 + 3 mL volume, 2  big and 2 small hypodermic needles with plastic ends closed by welding,  5-mL syringe with a long blunted needle,  10-mL injection bottle in a stand, 9-Volt battery, 2 insulated wires with crocodile clips, piezo spark giver,conc sodium sulfate solution (with red food dye).
Experiment:
1. Photo 1 : Pierce the thick part of the pipette with the 2 big hypodermic needles and the thinner part of it by the 2 small one.
2. Use the syring to fill the pipette completely with the coloured electrolyte. Also add about 3 mL of the red solution to the injection bottle.
3. Carefully turn this apparatus round an immerse it into the bottle.
4. Connect the long electrodes with the battery for electrolysis.
Photo 2: 5. As soon as the upper part of the pipette is full of gas, remove the cables from the lower electrodes.
.............6. Connect the piezo spark giver with the small electrodes dipping into the gas.
.............7. Tightly hold on the pipette while you let thie gas explode.
Observations:
Photo 3: During the explosion the negative pressure compresses the head of the pipette and red liquid is sucked into it.
Explanation:  Oxyhydrogen gas disappeared while water was made again. As a liquid its volume is reduced very much causing the negative pressure and the red liquid to move upwards.