bla287's video: 01 Electrolysis Of Sodium Chloride Cl2 is produced

When electrolysing a solution of NaCl, you'd normally expect water to be oxidized to oxygen and oxonium because of the electrode potentials (given values are E0): Cl2 + 2 e− ⇌ 2 Cl− +1,36 V O2 + 4 H3O+ + 4 e− ⇌ 6 H2O +1,23 V Normally, the oxidation reaction with the lower potential happens, so one would expect that water oxidation would be preferred over chloride oxidation. But in reality, the potentials depend on many factors such as concentration, type of the electrodes used, temperature, etc. That's why you can "trick out" the potentials by using a graphite anode and a saturated NaCl solution. The smaller chloride ion can attach to the graphite more easily than the bigger H2O molecule, so the chloride ion will be oxidized to chlorine ("over voltage" effect). This favours the chloride oxidation. Using a higher concentration of chloride ions will also shift the preffered oxidation reaction towards chloride oxidation (This is understandable if you look at the Nernst Equation). However, some of the chlorine produced that way will react with the OH- ions produced by the cathode to form ClO- and Cl- (in succession ClO3- and ClO4- as well): Cl2 + 2 OH(-) ⇌ Cl(-) + OCl(-) + H2O 3 OCl(-) ⇌ 2 Cl(-) + ClO3(-) To reduce such disproportionation effects, HCl can be added. On the one hand, this increases Cl(-) concentration, on the other hand it reduces OH(-) concentration. Both effects hinder the chlorine from reacting to hypochlorite , because the reactions are pushed towards the educt side. To prove that chlorine has really been produced, I let it react with iron to form yellow iron(III) chloride (FeCl3). So you don't need to melt NaCl if you want to obtain Cl2 (but you have to if you want to get Na). BTW the gas bubbling up from the metal cathode is hydrogen (H2). Here's a very informative site about (per)chlorate cells: http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/chlorate.html