Synthesis database: Potassium chlorate synthesis (via hypochlorite)

This is one of the most simple ways to synthesize potassium chlorate. Basically, this reaction is based on the thermal decomposition of sodium hypochlorite. After that, via the process of ion exchange, one can obtain potassium chlorate from sodium chlorate. The main reaction is:

3NaClO _(aq) -› 2NaCl _(aq) + NaClO_{3 (aq)}

while the other reaction is shown below:

NaClO_{3 (aq)} + KCl _(s) -› NaCl _(aq) + KClO_{3 (aq)}

As a source of sodium hypochlorite, a solution used for bleaching was used which contains around 5% of the mentioned compound. Thereby, the mass of NaClO per one liter of this type of bleach, is around 50 grams, which is equal to 0.675 moles. The reaction of thermal decomposition of the hypochlorite shows that from 3 moles of NaClO, one mol of sodium chlorate is produced. When one takes into account that in this case, there is 0.675 moles of NaClO, it turns out that one should get around 0.225 moles of NaClO₃.

Furthermore, in the reaction that shows the process of ion exchange, one can see that for the synthesis of one mole of potassium chlorate, one mole of potassium chloride needs to be added to a mole of sodium chlorate. By doing the math with the already mentioned values, it turns out that one needs to add 16.65 grams of potassium chloride (0.225 moles). To make weighing more simple, the value was rounded to 17 grams.

First, 1000 mL of the mentioned solution of hypochlorite is heated until it starts to boil, preferably in a stainless steel beaker. This solution is left to boil for around half on hour, until the volume of the solution drops to about 140 mL. After that, the solution is cooled gradually until room temperature is reached. Formation of solid sodium chloride can occur in this stage. Because of that, the solution can simply be filtered when it has cooled down. The chloride forms because, while cooling, the solution becomes supersaturated. In addition, the commercial liquid hypochlorite solutions also contain a certain amount of sodium chloride. Having in mind that even more NaCl is created in process of thermal decomposition, the supersaturation doesn't come unexpected.

After the solution cooled down, 17 grams of potassium chloride is added, and at the same time, the temperature of the solution is increased gradually. After all the potassium chloride is dissolved, the temperature is still increased until the boiling point is reached. After that moment, the solution is taken away from the heat source and is left to cool down to room temperature. Later, the solution is cooled further by placing it in the fridge at the minimal temperature that can be achieved. Already at 0 °C, a decent amount of potassium chlorate crystals should be visible.

These crystals are the final product - potassium chlorate. Since they are still in the solution, they need to be filtered. The remaining liquid can be heated again until the volume of the solution is even further reduced. After that, the remaining solution is cooled once again, in order to extract as much crystals from the solution, as possible.

After the mentioned step, the two batches of potassium chlorate can be mixed together. The mass of the crystals that were produced in the described synthesis was 14.1 grams. After the eventual weighing of the KClO₃, the crystals are placed in a container, which is then placed in a larger container containing a common dessicant - silica gel. After spending a day in a closed container with silica gel, the potassium chlorate crystals were completely dry and ready to be safely stored.