Warning: Electrolysis of potassium chloride generates flammable and explosive hydrogen gas.
As well as toxic chlorine gas.
This experiment should be performed in a well-ventilated area.
Electric currents can induce sparks and fires if mishandled.
Greetings fellow nerds.
Potassium chlorate is a pretty useful oxidant most famous for its applications in chemistry with a few lesser applications in fireworks and other pyrotechnics.
It's also one of the few oxidants easily made by amateur chemistry.
Now perchlorates like ammonium perchlorate find more use in pyrotechnics but for now we'll just focus on potassium chlorate.
Now we've already covered how to make potassium chlorate from bleach in a previous video.
While that process is quick and easy, it's not very efficient or cost effective.
You need large quantities of bleach to get small amounts of potassium chlorate.
In this video we're going to make potassium chlorate by electrolysis.
The idea is to apply electric current directly to a solution of potassium chloride.
This converts it to potassium chlorate.
Now before we start building, i need to go over the most important part of the potassium chlorate electrolysis cell, the anodes.
These electrodes are where the oxidation is occurring and are notorious for getting destroyed in the highly corrosive conditions of a potassium chlorate cell.
So you need anodes that resist corrosion.
The three most common ones used by both amateurs and professionals are carbon, mixed metal oxide and platinum.
The common metals like steel, iron, copper, aluminum and so on cannot be used.
They all get totally destroyed in a chlorate cell.
If you need to ask if an electrode will work, then chances are it won't work.
Now there are exotic anodes like magnetite, boron doped diamond, glassy carbon and lead dioxide.
But for the most part, carbon, mixed metal oxide and platinum are the most common.
Carbon electrodes are the cheapest and widely available.
You can get them from batteries and i've already shown how in a previous video.
Plates can be bought off ebay and you can also use carbon gouging rods like i have here.
They come coated in copper that you'll have to remove first.
To do so you can dip them in PCB etchant or simply run them in a salt water electrolysis cell for a few hours.
That's what i did for these ones.
Now carbon electrodes are the cheapest but they have a significant drawback in that they still breakdown in an electrolysis cell and release carbon particles.
To demonstrate i have here a graduated cylinder and i've set up a titanium cathode and carbon anodes.
Let me fill it with a solution of potassium chloride.
Now we turn on the current and wait.
It's making potassium chlorate but you can see carbon particles slough off the carbon electrode and contaminate the solution.
This will also contaminate your potassium chlorate.
Another drawback is that carbon electrodes don't take high currents as well as the other electrodes i have.
They can safely handle about 30-40ma per square centimeter of submerged surface area.
If you go higher, they corrode exceptionally fast.
So to get a high production rate you need lots of carbon electrodes or use very large ones.
Anyway, here it is after running it for several hours.
That's precipitated potassium chlorate contaminated with carbon.
While it looks bad, if you just want your potassium chlorate for fireworks and other pyrotechnic uses then a bit of carbon contamination is inconsequential.
Carbon electrodes tend to slough off the most during the first few days of use, but then taper off.
So subsequent runs will be somewhat cleaner than this.
If you want it pure you can still redissolve it in hot water and filter.
Alternatively you can use a better electrode.
Platinum electrodes are the most expensive of what i have here.
But they're very popular and easy to find online.
Unfortunately, because they're so popular, they're also lots of fake electrodes online.
I was scammed a few times before i found authentic ones.
I've included a link in the video description for where i got my electrodes that i've tested to be authentic.
Anyway, i've set up another demonstration cell.
Let me add in potassium chloride solution and turn on the current.
And there we go.
Commercial platinum electrodes for electrolysis are usually made of titanium coated with a thin platinum layer to save costs.
They handle the most current, around 300ma per square centimeter without too high a corrosion rate.
Ten times more than carbon.
So you can build high production chlorate cells in a small space.
The corrosion rate is so low that you don't have to worry about it contaminating your potassium chlorate to a significant degree.
And here we are after several hours.
Pure crystals of potassium chlorate have settled on the bottom.
After some filtering this can be used directly for chemistry or pyrotechnics.
And here are the two electrode results side by side.
As you can see, there is no contest in terms of quality.
The final electrode i'm showing is this mixed metal oxide electrode.
It's also called an MMO electrode or dimensionally stable anode.
These consisted of titanium coated in metal oxides, usually ruthenium dioxide and iridium dioxide.
They handle somewhat less current than platinum at around 200ma per square centimeter.
But they're much cheaper than platinum electrodes.
They also don't corrode as badly as carbon and produce high quality potassium chlorate like platinum does.
Overall i think these offer the best value.
These are the ones i'll be using in my chlorate cell.
The weird drawback is that they are hard to find.
Occasionally they pop up on ebay or from other online retailers, but they're not nearly as popular as carbon and platinum.
They're also limited in chemistry.
Other experiments like making sulfuric acid from copper sulfate or recycling PCB etchant would completely destroy them.
So if you want an electrode that works for a wide range of experiments, go with platinum or carbon.
MMO electrodes are limited to strongly alkaline experiments or salt electrolysis.
So let's get started.
Once you have your electrodes the rest is pretty easy.
You're going to need a container for your chlorate cell and I'm using this 4L polyethylene storage container.
Polyethylene and propylene plastics are good for chlorate cells as they are immune to the effects of the solution.
The container should be larger than your electrodes to maximize the surface area you can expose to solution.
Now we just place in the electrodes.
I'm using mixed metal oxide electrodes for my anode and for my cathode i'll be using a single thin strip of titanium.
You can also use stainless steel our iron but those tend to reduce the chlorates produced back into chlorides so titanium is better.
Copper is also less than optimal.
I'm using such a thin and narrow electrode to encourage hydrogen formation and discourage chlorate reduction.
A mesh is better but I didn't have one.
Generally you want a large surface area for the anode and a small surface area for your cathode.
Now something optional you can add is a salt cup.
It's nothing more than a plastic cup with a few holes poked in the bottom.
The glass rod i've skewered through it let's me suspend the cup near the top of the cell but bottom will be below the water line.
The idea of the cup is that you can add salt to it and have it slowly dissolve into the electrolyte.
Now we fill the cell with a saturated solution of potassium chloride.
Potassium chloride can be purchased as a salt substitute for those people with low-sodium diets.
A very plentiful source is water softener salt.
Most water softener salt is sodium chloride but the potassium chloride variety is also available.
Check the ingredients to be sure.
You can get large quantities very cheaply.
Once that's filled with solution, you can now connect the power leads.
Negative to the cathode, in this case the titanium strip.
And positive to the anode, in this case the mixed metal oxide electrode.
Now you can run the cell open like this.
But the hydrogen and small amounts of chlorine gases produced will enter the room so you need good ventilation.
Instead of dealing with that i'm going to use my electrolysis box i built in a previous video.
I've included links in the video description.
Basically the box pumps out any gases and allows me to direct them outside through a tube.
It also has a power supply built-in to let me control the current.
Using an electrolysis box is completely optional though and if you run your cell in a well ventilated area,
or specially design your cell with sealed top, it's unnecessary.
For our cell i'm going to set the maximum applied voltage to 6 volts.
As the ions in cell react and the internal resistance increases the voltage across the electrodes will rise.
But we don't want the voltage to get too high as this will damage the electrodes, especially the anode.
So by setting a maximum voltage we protect the electrodes if the resistance becomes too high and can no longer sustain the current flow.
Let me attach the wires.
I'm setting my current to two amps.
Now these electrodes can take much more current, several tens of amps.
I'm using just two amps for a couple of reasons.
One the point of contact is just one clip and this is generally high resistance resulting in excessive heating here.
Excessive heating will damage the coating on the electrode.
A better designed cell would actually spot weld the electrode to a high current busbar.
I'll build an advanced cell in the future which can handle higher currents.
But in this one, i'm going to use just two amps to keep heating to a manageable level.
The second reason why I'm using just two amps is to keep electrode wear to a minimum.
Generally the lower current density you use, the less the wear.
Okay now that I got the current and voltage set.
I'll cover my electrolysis box and let it run.
At this point we should go over the reactions.
Now ideally when this runs it should electrolyze the solution and generate hydrogen gas at the cathode and chlorate at the anode.
Overall we're making potassium chlorate.
We should expect to move 6 moles of electrons for every one mole potassium chlorate produced.
In practice though this is not quite that efficient.
Rather than producing potassium chlorate directly what this really does is create potassium hypochlorite first.
In order for this to make potassium chlorate the pH must be maintained at around 6.7 to protonate some of the hypochlorite into hypochlorous acid.
Then if the cell were run at higher temperature, say above 70 celsius,
the ions would disproportionate into potassium chloride and potassium chlorate.
In a basic cell this doesn't happen because not only are we just running at room temperature,
but the pH actually drifts away from ideal very quickly.
A side reaction at the anode generates small amounts of chlorine gas.
This has the overall effect of producing potassium hydroxide,
and that greatly increases the pH of the cell over time.
Thus, without the correct temperature or the correct pH,
the disproportionation reaction doesn't occur and the potassium hypochlorite concentration builds up.
Eventually it becomes high enough that it can itself start getting electrolyzed.
At the anode it is electrolyzed into potassium chlorate.
But this reaction wastes a significant amount of power since it generates oxygen as an unwanted by product.
Overall, we're still making potassium chlorate, but in a very inefficient and roundabout method.
It is nonetheless a simpler design than building a heated a cell that must be maintained at the correct pH.
So for most amateurs a basic chlorate cell like this is acceptable.
Now another source of inefficiency is the chlorate and hypochlorite ions can travel over to the cathode and get reduced back into chlorides.
This also wastes power since we're essentially accomplishing nothing overall.
It can be mitigated by using cathodes with smaller surface areas.
The chlorate and hypochlorite destruction will still occur, but will be limited since there is less surface area to react with.
The high current density then results in the water being electrolyzed more vigorously since it has a comparatively huge concentration.
The tradeoff is that high voltage is needed, wasting power again if the surface area is too small.
In advanced cells special electrode materials are used and even divided cells can be implemented to nearly eliminate unwanted side reactions.
Another solution to unwanted cathodic reduction is to use small amounts of electrochemically active additives like potassium dichromate.
The reactions are complex so i won't go into them but they suppress the unwanted reactions at the cathode and thus improve efficiency that way.
The drawback is they now contaminate your product and if that's a problem you'll need to do a purification step to remove them.
In anycase, this cell will consume potassium chloride and precipitate potassium chlorate as it runs.
To maintain efficiency and to keep electrode wear to a minimum, we need to replenish the potassium chloride as it's consumed.
Now because the inefficiencies make the consumption rate difficult to predict we'll need a way to measure it.
The simplest method i found was just to take accurate density measurements.
Every week or so take a precisely measured volume of electrolyte and weigh it.
Divide the mass by the volume to get density.
Saturated potassium chloride solution at room temperature has a density of around 1.16g/mL.
As potassium chlorate precipitates this will decrease.
I recommend topping up when the density reaches around 1.1g/mL.
The salt cup i showed earlier is perfect for this.
Just add some potassium chloride salt to the cup and let it slowly dissolve on its own over a few hours.
A rough figure to add is 10g per 100mL of water in your cell.
Although you'll need to adjust according to your cell conditions.
I don't recommend adding it directly to the cell because when it sinks to the bottom
some of the potassium chloride will be wasted if it gets trapped in the precipitating crystals of potassium chlorate.
For the same reason i don't recommend leaving extra potassium chloride in the cup exceeding the saturation point.
It'll precipitate in the cooler parts of the cell and get wasted.
Anyway, after the potassium chloride has been dissolved take additional density measurements and adjust accordingly.
After my cell got going i only topped up the potassium chloride every two weeks.
Do not let the density go too low as lack of ions to electrolyze will also damage the electrodes.
This is especially important for carbon electrodes.
Now I'm very patient so I'm going to let this run for a month and then collect my potassium chlorate.
It is now 40 days later and we're going to harvest our yield of potassium chlorate.
So here is the cell.
Current is still flowing and the voltage hasn't risen significantly.
So our electrodes are likely still good and there hasn't been too much damage to the clips.
Let me open it up.
There is some spray out and condensation in the bottom but that's minor.
There is some salt creep and corrosion around the electrodes, but that's to be expected.
Electrolysis is still proceeding vigorously.
Okay let me turn that off and get the electrodes out.
On a side note you can see the potassium chlorate crystals crystallizing on the anode itself.
This is something you want to avoid as this blocks the solution from reacting with the anode.
In my cell this was unavoidable since the electrodes were as big as my container.
But if you can, generally keep your electrodes off the bottom of the cell so they're not covered by precipitating potassium chlorate.
Anyway, here is the cell with the electrodes removed.
And we have a beautiful crop of large potassium chlorate crystals.
So now we decant off most of the solution.
And finally, we filter the crystals and air dry them.
Now let's take a look at the supernatant.
There is a slight greenish tint indicating the presence of unreacted potassium hypochlorite.
You can see the color slightly better in this earlier video.
Anyway, if you intend to make more potassium chlorate right away
then you can simply pour this supernatant back into the cell,
check the density, top up potassium chloride and keep going.
Since this solution is already full of potassium hypochlorite and chlorates
you'll have a head start in potassium chlorate production.
If on the other hand you don't intend to restart production soon
or if you actually want to discard the solution and stop completely.
You may want to convert the last bit of potassium hypochlorite to potassium chlorate and squeeze out a tiny bit more yield.
To do this simply heat up the solution until it starts boiling.
As it boils the potassium hypochlorite will disproportionate into potassium chlorate.
Now the reaction actually works best if you control the pH to 6.7 but high temperatures will suffice.
In advanced chlorate cells the solution is kept hot while it's running to produce potassium chlorate continuously.
But boiling temperatures would actually damage the electrodes in addition to wasting power.
In that case pH control is absolutely necessary so less damaging temperatures can be used while still being hot enough to convert the hypochlorite.
Okay, once the solution is at a good rolling boil, turn off the heating and let it cool.
Small crystals of potassium chlorate will precipitate out.
And there it is, a small extra amount of potassium chlorate.
It's not a huge amount so doing this treatment to maximize yield is optional.
I'll let you decide if you want to do it or not.
Now at this point i am going to store my depleted solution for future runs of potassium chlorate.
This solution still has potassium chloride and is saturated with potassium chlorate so i might as well keep it.
I find empty bleach bottles best for storage since they are designed to hold exactly this sort of highly corrosive oxidizing alkali.
And there we have it, potassium chlorate.
Our recovered yield was 705g after 40 days at 2 amps.
Under theoretically ideal conditions for the same amount of time and current we should have 1463g of potassium chlorate.
So our yield was 48% of maximum.
While it is a bit a low i'm still very pleased because the actual cost of that much electricity was about $2.
Spending $2 to convert 705g of chemicals is a bargain even at 48% efficiency.
If i had perfect efficiency my electricity cost would have been $1.
As you can see spending hundreds of dollars to make a highly efficient cell isn't justified unless you're making potassium chlorate in hundred kilogram quantities.
Anyway, at this point you can save these crystals as is and use them for your experiments.
They are however somewhat large.
If you prefer a fine powder you'll have to grind these up.
Alternatively we can recrystallize them and get smaller purer crystals that way.
Transfer the crystals to large beaker or flask and add water.
I'm using some of the water to wash out my beakers and funnels to get maximum transfer.
The ratio is about 100mL of water for every 60g of potassium chlorate.
So i'm using a total of 1.2 liters of water.
Now simply heat it up until it completely dissolves.
This dissolving has the added effect of releasing any entrapped impurities like potassium chloride.
So when we recrystallize we'll have a somewhat purer product.
Okay everything is dissolved. Now we turn off the heating and let it cool.
When things slowly crystallize, like in the chlorate cell, they tend to form large crystals.
But when they're forced to crystallize very quickly.
They tend to form very small crystals.
This gives us the basis for controlling crystal size.
For pyrotechnics and similar, smaller crystals are prefered for faster and more consistent reactions.
Okay it's cool. Let me filter it. And there we go.
A much finer product of potassium chlorate.
The supernatant is now saturated with potassium chlorate and released impurities like potassium chloride
so i recommend storing that too and using it in future potassium chlorate runs.
Anyway, here is the comparison of the potassium chlorate both before and after recrystallization.
As you can see, recrystallization has considerably reduced the crystal size.
And there you have it.
Took over a month, but with some simple parts you can buy off ebay, we made potassium chlorate by electrolysis of potassium chloride.
In a future video i'll build a more advanced cell that produces potassium chlorate at greater rates with even higher efficiency in a smaller space.
Thanks for watching.