Question

What volume of hydrogen gas at standard temperature and pressure can be collected from the electrolysis of water using a current of 100mA for a period of 3 hours?

I know that the answer is 0.125 L but I don't know how to approach the problem.
I multiplied 100*10^-3 by 3600 to get 10800 C and then converted that into moles which came out to be .06
Where am I wrong and how should I approach the problem? Please help.

Answer 1

3 hours * 3600 seconds/hour = 10800 seconds

10800 seconds * 0.1 amps = 1080 Coulombs

H2O --> 2H+ + O--

1 mol electrons = 96,500 Coulombs
so
1080 C * 1/96500 = .0112 mol electrons
looking at equation, we need 2 mol electrons for every mol of H2
so we get
.0056 mol of H2
.0056 * 22.4 L/mol at STP = .125 Liter

Answer 2

by the way
http://www.quora.com/How-much-water-can-you-split-into-hydrogen-and-oxygen-using-electrolysis-with-one-kilowatt-hour-of-electricity