Electrolysis of water

[Inigo Montoya]

Great experiment: Grab a car battery, run leads from each pole of the battery and stick 'em in a bucket of water. Hydrogen bubbles off the negative lead, oxygen bubbles off the positive.

Pretty simple right? But wait. I understand that the leads introduce or remove electrons from nearby water molecules, and the result is the breaking of the molecule into its constituent bits, H & O. But why is it that only H comes off the negative and O comes off the positive? Presumably, I've just broken a molecule and H and O should BOTH be bubbling up from the same area. If I'm getting H off of one lead, where did the O that it was attached to go?

[Claptree]

Short answer: Excess atoms are adopted by nearby molecules, making H3O+ and H2O2- molecules respectively.

I think.

[Inner Stickler]

It probably reattaches to another H+ floating around in the soup. I suspect that what happens when you stick the leads in is at one lead you have electricity forcing a bunch of H₂O molecules apart, some of the H's escape as a gas while the O's attach themselves to other free H+'s and you have the opposite effect happening at the other lead. I'm not a chemist though so you probably would want someone to double check that.

[AllWalker]

Water molecules are held together because the H+ ions are attracted to the O- ions, because in electromagnetics opposites attract.

Introducing an electrical current disrupts this attraction - suddenly, the H+ ions have a stronger negative charge to go to than the oxygen ion. The water molecule falls apart into it's constituent ions.

H+ ions travel towards the negative, as is their style. O- ions travel to the positive. When they reach the electrode, they combine with other ions and, with the help of the current, form stable gas molecules.

So the short answer is - a mixture is not formed because the atoms don't go straight from water molecule to hydrogen and oxygen gas. They form ions first.