Making Potassium Chlorate

• Safety first
• Introduction
• Needed
• How does it work
• How to set up
• Run the electrolysis
• Collecting and cleaning the crystals
• Experiments Jan 2018
• Video of experiments Jan 2012
• Experiments Jan 2011
• Experiments Dec 2000

Burning sugar mixed with KClO₃. Pictures taken with 0.5 seconds interval.
Do not perform such experiments, unless you are an experienced chemist.

Safety first

Potassium chlorate (KClO₃) is a strong oxidizer. Do not heat or rub it with combustibles, like carbon, sugar, etc. With Phosphorus or even sulphur in may ignite easily. Avoid contact with acids as well.

Molecular formula:	KClO3
Formula weight:	122.55
CAS number:	3811-04-9
Melting point:	356oC
Safety:	R 9,20/22; S 13 16 27
RTECS #:	FO0350000
EINECS:	223-289-7

Introduction

Potassium chlorate KClO₃ (also called Potassii Chloras or Kalii Chloras or Chloras Kalicus/Potassicus) is the potassium salt of chloric acid and is an oxidizer, used in chemistry to produce oxygen, but also used in fireworks. It is obtainable at chemicals supply shops, such as Merck or other large suppliers. It used to be available at the local chemist but this is getting harder and harder. With rather simple means you can make this yourself by electrolysis. Due to its poor solubility of 5 % in cold water, compared to sodium chlorate and chlorides, it is to prepare rather purely.

Needed

item to be needed	for what	where to obtain	alternative
Jar or beaker of about 0.5 liters	This will be the electrolysis cell	available in household
0.5 - 1 liter Beaker (preferably made of Schott Duran or compatible heat-resistant glass)	Needed for heating the solution	Lab supply shop or ebay	A stainless steel pan may also be OK.
Funnel and fine filters	to filter out the insoluble substances and carbon anode dust	The fine lab filters (such as Mackerey-Nagel MN 640d) are best, they cost no more than $10 per 100 in lab supply stores	When coffee filters are used, use at least three at at time.
Platinum anode, but due to the high price, carbon rod(s) are a good alternative. Better are MMO anodes	For anode.	Available in welding supply shops, MMO anode os ebay for $50	Dismantling a flat 4.5 battery may also do the job, but the MnO2 inthe cells may cause hard to remove stains.
Laundry or other nonmetal (plastic or wood) clamps	To attach the electrodes to the jar, preventing short-circuiting	Household or hardwarestore
Stainless steel spoon or other strips	Cathode.	Household shop
DC Power supply for 5-6 Volts and at least 5 Amps. A large PV solar panel will do fine in sunlight. Note higher voltages have an adverse effect and corrode the anode more quickly.	Power supply.	Auto supply, electronics stores, computer repair shop or ebay	A cheap battery charger does the job very well, or better a computer power supply which supllies the required 5 V
DC Ammeter (when not already in the supply) with range of at least the value the power supply can supply, e.g. 10 Amps.	Check the current.	Electronics store or eBay
Thermometer with 100oC range, preferably made of glass or plastic. Electronic ones with a stainless steel sensor are OK as well.	To check temperature.	Pharmacy / lab supply store or eBay
pH meter	To check the pH	Lab supply store, gardening center or eBay	A gardeners soil pH checker
Potassium chloride KCl	The electrolyte.	Chemist / Pharmacy, or just supermarket	A good source is 'LoSalt' salt low sodium diet salt, which is a mixture of 33% NaCl and 67% KCl.
A stove or another heat source.	to heat up aqueous solutions (e.g.Bunsen burner).	Lab supply shop.	Alcohol lamp.
An evaporating pan. Stainless steel or Pyrex does the job.	Evaporating the water from the salt.	Household supply store.
Mortar and pestle	to make fine powder of it	Lab supply shop or eBay	Hammer

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The old power supply (an 8 Amp. car battery charger) was finally deceased. It was too unstable and drew almost the same power from the mains (110W) when running 5V 8A than the new PS with 5.5V 18A which consumes 130W.
Here I used the new setup using a 5V 40A power supply for $30 from Amazon. For the cell I used the same 600ml 'pindakaas' (peanut butter) jar with the MMO anode and the stainless steel cathode in it. I let it run for several hours. I used to use a taller plastic jar but when reaching 100°C it became soft, so glass is a better option. Finally I got 62 grams in the first session and 77 grams dry purified KClO₃ in the next session. In that latter session I used another power supply: a variable voltage 3-24V, 20A for $50 from Amazon. I started with 7V, 15-18A and ended up with 5.5V 16A. When the solution gets hotter, it conducts better. After the first two hours, it was 85-90°C.

Experiment January 2012 (video)

Making Potassium Chlorate Jan 2012

Making Potassium Chlorate by electrolyzing Diet Salt (67% KCl) using an MMO anode. Here a video I took in Jan 2012 with another electrolysis session. For more info see below.

Making Potassium Chlorate Oct 2018

Making Potassium Chlorate by electrolyzing Diet Salt (67% KCl) using an MMO anode. Here a video I took in Oct 2018 with a timelapse of the filtering of the solution.

Video taken with the Canon Powershot G9.

These experiments I still did with the good old carbon rod method while I am waiting for delivery of the MMO anode I ordered. An extensive discussion on this subject (MMO anodes) is on the Sciencemadness forum. I perform all these experiments in the fumehood due to some escaping chlorine gas. When the process goes well not much Cl₂ gas escapes, a mere 'swimming pool smell' is detectable inside the fumehood.

Starting with the same setuo as 10 years earlier using a 500ml "Calvé Pindakaas" peanut butter jar but now with the 16mm carbon rod and stainless steel sheet sealed into the lid and sealed with caulking agent (Yes it stinks to acetic acid CH₃COOH during the caulking action...). And a PVC hose to release the gases (H₂ and Cl₂ and water vapor) into a water jar. After one hour of running at 10 A (voltage was lowering from 5.5 to 4.1 volts) the temperature of the bath raised to 60°C. The ammeter displayed on the picture is an 80/1 scaled ammeter so when it shows 800A it is actually 10A.

Next day I checked the pH with Mackerey-Nagel pH strips. I could estimate it is about seven so OK.However the strips look somewhat bleached due to the chlorine gas dissolved in the water. I dissolved some more JozoVitaal in the heated solution and poured it again into the peanut butter jar to start another session. I ran 9-10 amps again and the voltage was 3.6 volts. It seems that the higher the temperature, the lower the voltage.
After the two hours run I thought that the power supply deceased ..... no voltage was appearing from the supply and the fuse was OK. So I filtered the solution and some crystals appeared probably KClO₃. Later on it turned out that the power supply worked again: a thermal safety turned off when the transformer overheated.

The following day I saw clear crystals on the bottom of the piss like solution. I put the glass container in the fridge and allowed it to cool further. Then while running a third session for 5 hours with newly added 'JozoVitaal' I poured off the solution and put the crystals ito a filter and rinsed them with ice-cold water to rinse off the remaining Na+ and Cl-, ad allowed it to dry for another re-crystallization to purify it.
I noticed that the anode wear is remarkably small, probably to the correct pH and presence of K₂Cr₂O₇.

After a few more electrolysis sessions of 4 hours I collected all the (wet) crystals and dissolved in just ats much water that everyihing just dissolved at boiling. I let it cool outdoors (4°C) overnight and the next morning I poured off the still slightly yellowish liquid presumably NaClO₃, KCl and NaCl dissolved. Then again I added som fresh water and again let it boil and then cooldown. After cooling I rinsed the crystals with cold water as the flame test after the first recrystallizaion turned out too sodium-yellow. After the second recrystallization and rinding again the flame color was OK. So I let it dry and scraped it out of the evaporation dish , rubbed it with mortar and pestle. Result 69g. I tested a little with sugar and with a lighter it catched (purplish pink) fire immediately. So is was OK.

How does it work

anode: 2 Cl^- -> Cl₂ + 2e
cathode: 2 H₂O + 2e -> 2OH^- + H₂

Now the trick: In commercial plants, chlorine gas and caustic soda NaOH is produced this way. A diaphragm should be put to prevent intermixing the OH^- and Cl₂, otherwise the OH^- will react with the chlorine by:

2OH^- + Cl₂ -> 2 ClO^- + H₂

thus generating hypochlorite. The first target for making chlorate however is hypochlorite, to be oxidized to chlorate, so this process must generate hypochlorite and therefore mixing should take place.
When the solution heats up by heat loss (because the voltage is usually higher than required to yield the needed electrochemical energy), the hypochlorite will be oxidized to chlorate by:

3 ClO^- -> ClO₃^- + 2 Cl^-

and therefore the chloride ions will react again with the OH^-. So the total reaction (helped by the electric energy) is:

2Cl^- + 3 H₂O -> 2 ClO₃^- + 3 H₂

The oxidation state of the chlorine will be from -1 (Cl_-) to +5 (ClO₃^-), which requires 6 electrons per Cl- ion. Theoretically one mol electrons is equivalent by the physical constant of Faraday which is 96560 Coulombs (Ampere-seconds), which is nearly 27 Ampere-hours per electron (mole). To oxidize one mole of Cl^- to ClO₃^- costs 6 * 27 = 162 Ah. For one mole KCl (74.5 grams) to KClO₃ (122.5 grams) one needs 162 Ah in theory. In practice it is more, estimate about 200 Ah.

An extensive explanation of the reactions taking place and the pH control is described in this document.

Additional requirements

• The voltage over the cell should be at best 3.5-4 volts with a temperature of 55-60°C. When the solution is cold it should be no more that 5-5.5 volts which will decrease when temperature rises.
• The temperature is at best 50-70°C.
• The pH shoud be slightly under 7. When you don't have a lab pH meter, a soil pH meter for gardeners is OK. Normally, the pH tends to shift in the more basic range above 8 which results in poor performance and more anode erosion. Add a knifetip of K₂Cr₂O₇ per 500ml to the solution and if you don't have this, use a few drops of diluted HCl (available in the hardware store as 'muriatic acid' or 'Salzsäure' in German), but in the latter case check the pH again as it should get not too acid (i.e. under 6).

How to set up

Connect the anode with the red (+) clamp of the supply and the cathode with the black (or white) (-) clamp. Set the ammeter in series with the cell (with correct polarity). Set the power supply in the lowest possible current and check whether everything is connected well and no short-circuiting can take place.

Run the electrolysis

Watch the current and temperature. The current should not exceed the rating of the supply and the best temperature is between 50 and 70^oC.

Let it run for several hours at the optimum current and temperature, after determining these by experience. Check the water level and, when needed, add some water, as something evaporates. For 0.3-0.4 liter of solution about 240-360 Ampere-hours are needed, thus 24-26 h for 10 A continuous current. Note that the carbon rod will erode and the solution will become black because of small carbon particles.You can reduce this by keeping the voltage below 4.5 volts and the pH not in the basic range (i.e. keep is alightly below 7).

When you interrupt it (e.g. you do not want to let it run while you are not at home) remove the electrodes from the cell.

Collecting and cleaning the crystals

As KClO₃ has a poor solubility in cold water, but a good one in hot water, while other salts (like NaCl, KCl and NaClO₃) dissolve much better in cold water, one can let crystallize out the KClO₃ and obtain it rather purely.

Source: W. Ostwald: Grundlinien der Anorganischen Chemie (Fundamentals of Inorganic Chemistry) Steinkopff Verlag Dresden, Germany, 1919.

After it is finished, pour the liquid in a beaker or stainless steel pan which should be heated up to boiling point. Prepare another heat-resistant beaker or pan with a filter in a funnel on it. When you have coffee filters, use two or three filters at a time. When the liquid boils, pour it carefully in the filter. A clear liquid should appear from the low end of the funnel. It can be yellowish colored, because of oxidation of the iron in the cathode to yellow Fe³⁺ by some chlorine. When all liquid is passed through the funnel, let it cool down to as low as possible, possibly put it in the freezer or fridge after it has air-cooled. Do not allow to let the solution to freeze, as the container may crack.

Now large white crystals should appear on the bottom of the beaker. Pour gently off the liquid into another container while holding back the crystals. The liquid can be mixed with a fresh KCl solution for a new electolysis session. Pour some ice-cold water (from the fridge or freezer) over the crystals (no more volume than the crystals) to rinse off other salt solution.

Pour off any water and put the beaker with the crystals on a heat source and heat is with a very soft flame. Allow any water to evaporate. When the crystals are dry, scrape it from the beaker and collect it on an old newspaper or a cardboard. Then put them together into a mortar and crush the crystals.

A good test for the purity is :

• Flame test. Put an inert titanium or magnesia stick (stainless steel is also OK) in the KClO₃ slurry after rinsing. Hold it in a colorless flame and no yellow Na color should appear. Even small traces of Na will color the flame yellow. The color should be lilac like.
• Dissolve a few crystals in AgNO₃ solution. Only a slight precipitation (or none at all) should appear. When there is more precipitation, too much chloride ions are in the solution.

Last update: 2018 January 20