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Making Potassium Chlorate


Movie of burning sugar mixed with KClO3.


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

Note: These experiments are performed over 10 years ago (end of 2000). My new experiments which I am performing now will be listed soon.

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

OXIDIZING 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


Experiment January 2012 (video)

Here a video I took in Jan 2012 with another electrolysis session. For more info see below.

Experiments January 2011

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.

thumb./KClO3/pics1/-tn-IMG_4427.JPG
The jar on the left has a suitable size (you can first consume its content ;-) ), on the right the LoSalt jar with 67% KCl
thumb./KClO3/pics1/-tn-KClO3-cell1.jpg
First test tunning @ 10 amps
thumb./KClO3/pics1/-tn-KClO3-cell2.jpg
Still much carbon debris in it
thumb./KClO3/pics1/-tn-IMG_4418.JPG
Top view of the 'Calvé Pindakaas' cell
thumb./KClO3/pics1/-tn-IMG_4419.JPG
The electrodes: to the stainless steel cathode, bottom the carbon anode
thumb./KClO3/pics1/-tn-IMG_4420.JPG
Let it boil and check the temperature
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thumb./KClO3/pics1/-tn-IMG_4442.JPG
Running with a thermometer
thumb./KClO3/pics1/-tn-IMG_4443.JPG
Detail view of the cell without carbon debris after three hours
thumb./KClO3/pics1/-tn-IMG_4441.JPG
The pH slightly below 7
thumb./KClO3/pics1/-tn-IMG_4423.JPG
The first harvest: crysrtals of (still impure) KClO3
thumb./KClO3/pics1/-tn-IMG_4424.JPG
The rest of the crystals in the filter
thumb./KClO3/pics1/-tn-IMG_4426.JPG
Crystals precipitating in the cooling saturated solution
thumb./KClO3/pics1/-tn-IMG_4445.JPG
Heating up the raw crystals in water
thumb./KClO3/pics1/-tn-IMG_4446.JPG
It is boiling and all KClO3 is dissolved
thumb./KClO3/pics1/-tn-IMG_4447.JPG
Still warm, but it is crystallizing out
thumb./KClO3/pics1/-tn-IMG_4448.JPG
Rinsing the crystals to leach out sodium salts
thumb./KClO3/pics1/-tn-IMG_4449.JPG
Evaporating the solution
thumb./KClO3/pics1/-tn-IMG_4450.JPG
Drying on top of the woodstove
thumb./KClO3/pics1/-tn-IMG_4451.JPG
Rubbing with mortar and pestle
thumb./KClO3/pics1/-tn-IMG_4452.JPG
The final product: 69g chlorate.

Old experiments December 2000

'Vital' salt box containing 41% KCl, suitable as source for KClO3. Schematic setup for running the electrolysis. Running the electrolysis in a jar with carbon anode and stainless steel cathode.

How does it work

Electrolyzing an alkali chloride solution results in the following reactions:

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).
When you meet these requirements even carbon / graphite anodes will erode very slowly and therefor last long.

How to set up

NOTE: Perform the electrolysis outdoors or under a well ventilated hood, because flammable hydrogen gas and some toxic chlorine are generated. Use a fused power supply, to prevent fire at short-circuiting. Most battery chargers have 10 or 20 Amp fuses. Attach copper wire to the carbon rod, on a place which is not to be immersed, as copper will be attacked otherwise. It should be tightly connected as 10 amps will pass through it. Clamp it to the jar. Attach the stainless steel cathode on the other side.
Dissolve around 100 grams of KCl (or diet salt which consists of about 50% NaCl and 50 % KCl) in 0.3-0.6 liters of water and let it boil. Pour this into the jar (carefully, as it will break otherwise at the quick temperature change). Put the thermometer in the jar. Newer diet salt consists of even 67% KCl and 33% NaCl, which is even better.

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

Now turn on power. When the current is low, turn it up (e.g. by turning on 'quick charging' and/or 12 V instead of 6 V).
NOTE: Check that the voltage with the load on does not exceed 6 volts, otherwise the anode might erode far more quickly, particularly when you are using an MMO anode. A computer power supply supplies 5 volts with 10-20 amperes. When you are using a car battery charger, you can use a power controller and lower this until the voltage is about 5 volts.

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

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

Heating the electrolyzed solution. The black stuff in the left beaker is just electrode debris which hast to be filtered on the right filter. Filtering the electrolyzed solution The raw crystals after cooling down the filtrate.


A winter way for cooling the solution

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.

Solubility diagrams of NaCl, KCl and KClO3 in mass percents.

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.
You can recrystallize it by dissolving it in boiling water just enough water to dissolve everything. Then allow it to cool and put it into the fridge or freezer or outdoors in cold winter weather. After cooling pour off the water and dry the crystals. Now they should be more pure. Note: Do not mix it with any combustible stuff while rubbing it in a mortar,as a spontaneous reaction might occur ! The powder is the chlorate ready to use.


The KClO3 crystals dried.
result
The final result of the homemade chlorate in dec. 2000.

Last update: 2012 April 23

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