[Sneezium]

Nothing was added to the tap water. 12 Volts was used. There was no barrier in the electrolyte between the electrodes. The electrodes were coiled strips of magnesium metal. It was done in a plastic tub and the gas from the electrodes was collected in plastic bottles.

I am not interested in improving the apparatus. (It's not mine) I just want to know what happened. (I only saw a video of the experiment) The basic chemistry books that I can find never explain anything this complex. They use nonreactive electrodes and barriers or salt bridges and use known electrolytes. I need help figuring out what reactions occurred at the anode.

It seems to me that water would be reduced at the Cathode to produce hydrogen gas.

Cathode (-): 2 H₂O(l) + 2 e^- H₂(g) + 2 OH^-(aq)

It seems to me that the metallic anode would go into solution as magnesium ions.

Anode (+): Mg Mg⁺² + 2e^-

Wouldn't the magnesium ions form insoluble magnesium hydroxide at the anode? Where did the gas come from that was produced at the anode?

[chenbeier]

I think you will have the electrolysis of water. At cathode the hydrogen will be developed and at the Anode oxygen. You are right you will also get corosion there and magnesium hydroxide will be formed.

[Sneezium]

Both gasses ignited. They must have been hydrogen.

[AWK]

If the electrode spaces are properly separated, and hydrogen is still present at the anode, then metallic magnesium also reacts with water. Normally, a magnesium ribbon covered with a thin layer of oxide reacts only with hot water, but you thoroughly clean its surface during electrolysis.