電解法制氫...

Hofmann voltameter is an apparatus for electrolyzing water, invented by August Wilhelm von Hofmann (1818–1892). It consists of three joined upright cylinders, usually glass. The inner cylinder is open at the top to allow addition of water and an ionic compound to improve conductivity, such as a small amount of sulfuric acid. A platinum electrode is placed inside the bottom of each of the two side cylinders, connected to the positive and negative terminals of a source of electricity. When current is run through the hofmann voltameter, gaseous oxygen forms at the anode and gaseous hydrogen at the cathode. Each gas displaces water and collects at the top of the two outer tubes.

The presence of gas in the collecting tube can be detected with a smoldering match or "glowing wood splint"; oxygen will cause the match immediately burst into bright white flame and will burn vigorously, while the presence of hydrogen gas will merely cause the match to glow a bit more brightly.

The Hoffman Voltameter, was invented (how surprisingly) by Mister Hoffmann in the 19th century. It’s an apparatus for electrolyzing water. It consist of three, connected, vertical tubes. You can close the two tubes on the sides to collect the gasses which are formed, through the tube in the middle you can fill the Voltameter with an addition of water and an ionic compound in order to improve the conductivity.

When current is run through the Hoffman Voltameter, oxygen(gas) is formed at the anode and Hydrogen(H2 gas) is formed at the cathode. The electrode used to be of platinum but now a days they are often made of graphite. Each gas will displace water and collects at the top of the tubes. This is how we measured how much H2 was formed.

I hope this can help your understanding. :)

2007-09-28 00:22:52 補充：
In modern form, Faraday's law states:m = (1/96485) * Q * M / nwherem is the mass of the substance produced at the electrode (in grams), Q is the total electric charge that passed through the solution (in coulombs),

2007-09-28 00:23:41 補充：
n is the valence number of the substance as an ion in solution (electrons per ion), M is the molar mass of the substance (in grams per mole), For reaction 2H+ --> H2(g)H2(g)M = 2.016g / moln = 2 per H2 moleculesif we choose to get 1 mole of H2, then m = 2.016g

2007-09-28 00:24:41 補充：
2.016 = (1/96485) * Q * 2.016 / 2Q = 192970 As <--- unit is ampere-secondQ = 53.6 A hrUsually the voltage need is only a few volt, (I don't remember the exactly value)we just take 5 V dc for this setup for calculation

2007-09-28 00:27:05 補充：
Power = V * Q= 5 * 53.6 Ahr= 268Watt-hr (~1/4 kwh) <---- this value is a guess as I don't remember the exactly voltageBut the order of the value is about the sameIn general,For a dollar in electricity charge, you may get a few mole of H2 gas.For reaction 2H+ --> H2(g)