Na - The Third Millennium Online!
As for the electrolyte, in this case, I used a saturated aqueous solution of sodium chloride, which was prepared by dissolving 350 grams of NaCl in one liter of distilled water. The solution was heated slowly in order to speed up the dissolution. It is a good idea to add a bit of potassium dichromate to the electrolyte (about 6 grams per 1 liter of electrolyte), in order to reduce the corrosion of the cathodes. When the mentioned compound is added, during the process of electrolysis, around the cathodes hydrated chromium oxides are formed. These oxides protect the cathodes additionaly from chlorate and hypochlorite ions. However, because of the unavailability and the fact that this compund isn't really necessary, I did not add any of this compound. In addition, potassium dichromate is known to be carcinogenic, and that is another good and clear reason to avoid this compound.
Redox reactions in Inorganic Chemistry sections 5–7
As for the power source, I used a power supply from an old computer, which was modified in order to give an alternating current of the desired value of electric current. For the formation of one mole of chlorate ions, six moles of electrons are needed. The total charge of one mole of electrons, i.e. the Avogadro's number of electrons is equal to one farad (which is equal to 96485.3415 coulombs). Since 1 Ah = 3600 C, and by taking into account the fact that 6 moles of electrons are needed, I calculated that for the synthesis of one mole of sodium chlorate, 160.8 Ah are needed. Since the cells are in a series circuit, and by using the electric current of 3 A, I calculated that the time needed to convert one mole of NaCl to one mol of NaClO3 equals 26.8 hours. In each electrolytic cell there was 500 mL of the saturated NaCl solution, so in total, I was dealing with about 350 grams of NaCl, i.e. about 5.9 moles. Finally, the conclusion is that the reaction should be in progress for 158.12 hours in order to convert all the NaCl into NaClO3. As for the voltage, around 3 volts are needed for the oxidation of the chloride to the chlorate ion (and for the reduction of hydrogen on the cathode), but I used a bit higher voltage (9 V) because of the electrical resistance of the cells themselves.
This method of potassium chlorate synthesis is used in the industry for the mass production of the mentioned compound. The process is based on the electrolysis of an aqueous solution of sodium chloride. The product of this reaction is sodium chlorate. After that, via the process of ion exchange between potassium chloride and sodium chlorate, one can obtain potassium chlorate, and sodium chloride. This step is also used in the thermal decomposition method. As an electrolyte, one can also use solutions of other metallic chlorides (for example, barium or potassium chloride). However, using sodium chloride has its advantages - for example, the product (sodium chlorate) is much more soluble in water than barium or potassium chlorate. Because of that, after the reaction of electrolysis is finished, the product is completely dissolved, and that makes filtration of the electrolyte easier, because by filtration one can remove all impurities without removing some of the desired product as well. As I already mentioned, later one can use the obtained sodium chlorate to make potassium chlorate (or barium chlorate, which is also important in pyrotechnics) via a simple ion exchange reaction. Although this method is used in the mass production of the mentioned compounds, it can also be used to make smaller amounts of these products.