Hoffman apparatus, platinum electrodes, AC-DC rectifier, 100 DC "house current".
Dilute sulfuric acid.
- Fill tube with dilute sulfuric acid. Be certain each of the side tubes is completely filled with the solution.
- Connect the terminals to the current. The power supply should be set anywhere between 6-12 volts, depending upon how fast you wish the electrolysis to proceed.
- Allow reaction to occur. The hydrogen tube will fill at twice the rate of the oxygen tube.
Because sulfuric acid is both a strong acid and a powerful dehydrating agent, it must be handled with great care. The dilution of concentrated sulfuric acid is a highly exothermic process and releases sufficient heat to cause burns. Therefore, when preparing dilute solutions from the concentrated acid, always add the acid to the water, slowly, with stirring and cooling the receiving beaker. Hydrogen and oxygen gases will be produced in close proximity to one another. This is an explosive combination and any spark could set off this reaction.
There are two electrochemical reactions taking place: oxidation is occurring at the anode and reduction is occurring at the cathode.To keep the numbers of electrons balanced, the cathode reaction must take place, twice as much as the anode reaction. If the cathode reaction is multiplied by 2 and the two reactions are added together we get: Cathode: 2 H2O (l) + 2 e- ® H2 (g) + 2 OH-
Anode: 2 H2O (l) ® O2 (g) + 4 H+ (aq) + 4 e-
If we combine the H+ and OH- to form H2O and cancel species that appear on both sides of the arrow, we get the overall net reaction: 6 H2O (l) + 4 e- ® 2 H2 (g) + O2 (g) + 4 H+ (aq) + 4 OH- (aq) + 4 e-Since equal moles of gases at equal pressures occupy equal volumes, the fact that the volume of hydrogen is twice that of the oxygen confirms that there are twice as many moles of hydrogen as oxygen being produced. Net: 2 H2O (l) ® 2 H2 (g) + O2 (g)