Warning: Boiling sulfuric acid is extremely corrosive.
Wear protective clothing when handling it.
Toxic fumes can also be produced, perform this procedure outside or in a fume hood.
Greetings fellow nerds.
I need purified lab grade sulfuric acid again as I'm planning to do experiments in electroplating and analytical chemistry.
While using drain cleaner sulfuric acid is good enough for a lot of purposes, I'll need something better.
So i'm going to revisit one of the more dangerous amateur procedures and distill my drain cleaner acid to purify it.
I want crystal clear acid like this.
Of all the common preparatory experiments an amateur chemist might do,
i'd say distillation of sulfuric acid is probably one of the most dangerous.
While there are much more dangerous experiments, they're mostly optional while sulfuric acid is required for a lot of things.
For those of you who are new to chemistry and not familiar with sulfuric acid,
it's an extremely common acid and used in a large number of chemical reactions and processes.
It's one of the big three alongside hydrochloric acid and nitric acid.
It has a very high boiling point of 337 celsius,
so it can actually be used to make other acids by distillation with the appropriate salt.
It can also be used to sulfonate organic compounds in advanced chemistry reactions.
In pure form it can dehydrate and burn organic substances
and under careful conditions it can be used alongside nitric acid to make explosives.
I don't do that chemistry very much on this channel but it's out there.
It's also quite dangerous in pure form, capable of burning flesh.
It's infamous for being used in terrible acid attacks and please do not google those pictures because they are horrific.
However, like any powerful tool, there are good purposes as well and that's why we want to acquire some.
I intend to use it for analytical chemistry.
But because sulfuric acid is restricted and hard to get in some countries,
we have to purify it ourselves from lower grade sources.
Drain cleaner is the most common, but if you can't get that then battery acid is another,
and you can even make sulfuric acid using various processes that we've already demonstrated on this channel
like the copper chloride process or the electro bromine process.
Now those of you who have been with me for awhile have already seen me distill sulfuric acid using a homemade high temperature heating mantle.
That video is still valid and if you're already doing it that way then by all means keep doing it.
But I have since improved my techniques so i'm going to do it again with a few improvements here.
First is the heat source.
In my previous video we used a high temperature heating mantle that we built ourselves out of heating tape and a thermos.
It worked well but I have since upgraded to a ceramic hotplate stirrer.
I can't use a standard aluminum hotplate stirrer because those are limited to about 300 celsius or else the aluminum starts to soften.
But ceramic hotplates can go much higher, and this one can reach 540 celsius,
well past the boiling point of sulfuric acid at 337 degrees celsius.
Another problem with the mantle is that there is no stirring and so bumping and splattering was a problem even with boiling chips.
But stirring practically eliminates bumping.
This ceramic hotplate stirrer does both.
At this point I want to thank the viewer that donated this particular hotplate stirrer those years ago.
I really appreciate it.
This is such an awesome unit that I actually use it very rarely because I'm afraid of breaking it.
But when I do use it, it absolutely demolishes my other hotplate stirrers.
Anyway, this is what we'll be using for heating.
For the condenser we'll be using this compact single unit distillation head and condenser column.
The combined unit is simpler to use and mount than the usual two piece combination of distillation head and column.
The shorter condenser column isn't a problem for such a high boiling distillate as sulfuric acid.
Technically this is a short path distillation column
but we're not really using it in that mode and will be condensing at full boiling temperature,
so it's a compact condenser in this context.
There is no need for a fractional distillation column since the temperature difference between water and the sulfuric acid azeotrope is over 200 celsius
and the vapor pressures are wildly different.
Previously I used an ultra high temperature grease for the joints,
as normal vacuum grease is destroyed by boiling sulfuric acid.
But most amateurs have a hard time finding ultra high temperature grease and the cost is not justified.
I've since found a much better alternative and that's PTFE pipe threading tape.
This tape is immune to boiling sulfuric acid and seals the joints almost as good as grease.
It's also very cheap and easy to acquire for the amateur from their local hardware or plumbing store.
So I no longer recommend using high temperature grease, but instead using PTFE pipe threading tape.
And there we go, now we assemble it into our apparatus.
I'm going to distill about 800mL of drain cleaner grade sulfuric acid.
Iíve assembled everything in this plastic polypropylene bin for safety.
In the event of a catastrophic failure and something breaks, the boiling sulfuric should be contained by the bin, or at least slowed down.
Previously I relied on the heating mantle itself to safely contain the acid,
but the ceramic hotplate canít do that, so thatís why I'm using this bin.
I'll further discuss the safety issues later on.
Anyway up here we have the cooling water hoses attached to the condenser, and iím circulating room temperature water.
Let me turn on the stirring.
When boiling this much sulfuric acid stirring is very helpful to prevent bumping or popping
which is caused by the bottom becoming superheated compared to the rest of the liquid
and then the bubbles violently expanding as they float up.
Sulfuric acid is quite prone to it.
The stirring keeps the bulk liquid at uniform temperature.
Anyway, iím also turning on the heating and iím setting it to 200 celsius to start
since i donít want to thermally shock the glassware.
But every half hour i raise the temperature another 100 celsius until i reach about 500 celsius.
Iím also going to put a foil shroud around the flask to keep the heat in.
And now we wait.
At first the sulfuric acid expands and darkens as the impurities char and decompose.
Drain cleaner grade acid tends to be the waste product of industrial processes which is why it has these impurities.
Depending on the source it can still be very good acid so for reactions like making nitric acid
itís easier just to use drain cleaner acid directly and distilling it is unnecessary.
But for sensitive work like analytical chemistry or electroplating, pure acid is desired.
Iím going to put some more insulating foil on the distillation column to help the acid distill over.
This also helps to prevent water from condensing and falling back into the acid where it can violently boil and eject acid.
And there we go, weíre first distilling water.
My drain cleaner acid doesnít have very much so we donít have to wait long.
But if youíre distilling battery acid which only has about 30% acid then there will be a lot of water before we get to the sulfuric acid.
Other methods for making sulfuric acid like the electrobromine process,
the copper chloride process, or the lead chamber process, will also have considerable water that needs to be distilled off first.
On a different note, you can see my acid is getting lighter and lighter as the impurities have mostly decomposed.
This tends to happen as the impurities that were charring and darkening earlier are now essentially burn away as the temperature rises.
This is actually the basis for an analytical chemistry technique called sulfuric acid digestion, but I'll cover that in an upcoming video.
As we distill off more and more water, weíll want to know when the sulfuric acid begins distilling over.
Itís hard to tell just by looking at it, but my preferred way is to simply get a tissue and capture a few drops of the distillate as it comes off.
If itís just water itíll do nothing other than soak the tissue.
Even diluted sulfuric acid wonít have much effect.
So we can continue distilling and testing every so often.
If you have a thermometer in the distillation head then when the distillate temperature rises above 300 celsius is when weíre distilling sulfuric acid.
If youíre using the tissue method like I am, then we change the receiver when the tissue starts decomposing and charring.
Only highly concentrated sulfuric acid does this sort of damage.
An interesting quirk about sulfuric acid is that 98% is the maximum concentration you can get by boiling,
and it's not because it's an azeotrope even though we call it that.
What's actually happening is that above 98% concentration the sulfuric acid actually decomposes into water and sulfur trioxide.
So even if you started with 100% pure sulfuric acid, if you distilled it,
you would get 98% as some of it decomposes and leaves water behind while the sulfur trioxide escapes.
So 98% sulfuric acid is not an azeotrope of sulfuric acid and water, what it actually is an azeotrope of sulfur trioxide and water.
And thus sulfuric acid can even be considered as a solution of sulfur trioxide.
I just thought that was an interesting quirk about sulfuric acid.
Looks like weíre distilling sulfuric acid now, let me change out the receiver.
Now we want the highest concentration of sulfuric acid we can get which is the 98% azeotrope.
Weíre not quite certain if weíre there yet but a way to tell is to simply use a small receiver and carefully observe it while itís collecting.
It helps to put a high contrast background.
Anyway, if there are distortions in the liquid as it drips in then that means the drops are of changing density and still rising.
It looks like i have no distortions and that means iím distilling constant density sulfuric acid,
which can only be the maximum 98% concentrated sulfuric acid that weíre aiming for.
Here's a clip of the distortions from my previous video on distilling sulfuric acid.
As you can see, at this time the sulfuric acid was still boiling off the water and so the acid distilling over wasnít at the maximum concentration yet.
If you see something like this then keep boiling and changing out the receiver every so often until it becomes a constant density.
Since weíve reached that density we can now install our large receiver and collect our purified 98% concentrated sulfuric acid.
If you're using an already pure source of sulfuric acid like battery acid,
or some form of diluted sulfuric acid like acid made by sulfur dioxide and hydrogen peroxide,
then after water removal the acid is already pure and you don't have to distill it.
You can stop here and just use the acid in the boiling flask.
But if you're using an impure acid like I am that has residues, we'll need to keep distilling to leave those behind.
And there it goes.
As we wait, we got time to talk about some background information and extra notes about the process.
Something that I should address is my use of cooling water for the condenser.
Some amateurs have reported that the glass can crack or even shatter from the thermal stress
and instead recommend pumping air through the condenser to provide milder cooling action.
Iíve almost never had a glassware failure so I continue to use cooling water.
But if youíre uncertain about the quality of your glassware then forced air cooling should be considered.
Alternatively, just use a very long condenser as sulfuric acid condenses very well with just passive cooling.
But whatever you do, always plan as part of your safety procedures
how youíll contain and escape from a catastrophic failure in case something does break.
Which brings me to my next point, the polypropylene plastic bin used to contain it.
Some amateurs have expressed doubts whether a flimsy plastic bin can contain boiling hot sulfuric acid.
Theyíre absolutely right, boiling hot sulfuric acid does destroy plastic pretty quickly.
But the point of the bin isnít really to contain boiling acid, but instead to buy you time to get away if the glass fails.
If something bad should happen and the sulfuric acid begins spilling,
donít stand around to salvage it, step back and cut power and then wait for the acid to settle down and cool before approaching.
The acid may still melt through the bin, but it should take a few seconds giving you time to react and escape.
If you can get a steel tray that would be even better as long as it has deep sides to contain the acid.
But for the most part, a total glassware failure that unleashes the acid all at once is pretty rare.
Usually there will be a crack and the acid leaks out.
The plastic bin can contain a small leak of hot acid for several minutes, giving you ample time to deal with it.
If you want to extend the containment time, possibly indefinitely,
you can fill the container with sand or cat litter, put a few ceramic tiles on top, and then build the apparatus on the tiles.
The sand or cat litter will absorb any spilling acid and the mass will absorb the heat.
Protecting the bin and possibly allowing it to completely contain the acid spill.
Looking back I probably should have done the cat litter method, but maybe i'll do that in the future.
Alternatively if you want to completely prevent boiling sulfuric acid spilling in your lab, do the procedure outside your lab.
A great many amateurs simply do this distillation outside on top of ground they don't mind ruining with boiling acid.
When the weather gets better I'll likely do the same.
So what do you do if you have boiling sulfuric acid pooling around your lab bench.
Best thing you should do is to keep your distance.
Hot sulfuric acid may set things on fire or explode when it reacts with something, splattering the acid on you.
So as said before, don't approach it while it's hot.
Also do not neutralize it while itís hot.
Pouring water or a base on hot acid can cause it to explode and splatter,
and there have been some extremely horrific accidents where individuals have tried to do this.
Wait until the acid is cold.
If the acid has started a fire, extinguish the fire with a dry chemical fire extinguisher.
Iím actually standing beside one while iím doing this experiment.
So what do you do when itís finally cold and ready to be cleaned up?
Water and baking soda are usually used to neutralize and dilute it.
But first look around to make sure the acid hasnít eaten through any electrical wiring.
While PVC rubber insulation that most wiring has is resistant to cold sulfuric acid, itís not resistant to hot acid.
So be aware of that and cut power in the event of a major spill.
In terms of safety gear, as usual you should have face shields and thick fire retardant lab coats.
Nothing too special compared to other experiments.
The idea is to have as much material between you and the acid so the acid eats that first before it eats you.
There isnít much in the way of clothing that is immune to boiling sulfuric acid,
so approach from the idea that youíre sacrificing the clothing to it.
Another safety point I want to make is the sulfuric acid vapor.
The vapor is extremely corrosive and you donít want it burning your lungs from the inside out.
So perform this distillation outside or in a fume hood.
In theory, the vapor should be completely contained in the apparatus,
but in the event of a failure, or even something as mundane as a bump, that vapor will go into the air.
Additionally, as explained earlier.
There can be a small amount of sulfur trioxide from the sulfuric acid decomposing.
It's not much, but it absolutely should not be inhaled.
At this point a lot of you might be terrified of boiling sulfuric acid now and you should be.
As said before distilling sulfuric acid is about the most dangerous procedure an amateur chemist is reasonably foreseen to do.
Even most professionals consider it on the upper end of dangerous procedures.
But as long as you respect those dangers and have proper safety procedures,
it can be safely handled, contained, and controlled, even in the event of catastrophic failure.
So letís move on from the doom and gloom safety talk and discuss some of the other aspects of the experiments.
You might be wondering how the stir bar survives such insanely corrosive conditions.
The stir bar is a PTFE or teflon coated magnetic stir bar.
PTFE is one of the few substances that is chemically immune to boiling hot sulfuric acid.
However at these temperatures it can soften, it's still a plastic.
Other amateurs have indeed reported their stir bars coming apart after prolonged boiling.
Personally, my stir bars have proven completely immune but your results may vary.
Some lower grade stir bars will even lose their magnetism at these temperatures.
Some amateurs make their own glass encapsulate stir bars from bar magnets and thick glass tubes for their sulfuric acid distillation.
I was asked why iím using aluminum foil if i canít use an aluminum hotplate.
Aluminum softens at high temperatures, and you want the hotplate to remain rigid.
But it doesnít matter if aluminum foil softens as itís foil, just as long as it doesnít melt.
So we can drape this in foil without worry.
Aluminum doesn't melt until about 660 celsius, and weíre at maximum 540.
Now earlier I said I loved using PTFE tape to seal the joints.
But I've been asked if sulfuric acid itself can be used to grease them.
I know some amateurs have and reported success.
But the few times iíve tried the joints seized up and were inseparable.
So i cannot personally recommend using sulfuric acid to lubricate ground glass joints.
Considering how cheap and easy to obtain PTFE tape is,
I don't think I'll ever consider anything else for high temperature, highly corrosive experiments.
And there we are, most of the sulfuric acid has been distilled over.
The drain cleaner acid is relatively pure and has only a minor amount of salts that remain behind.
Although iím sure most of the organic impurities have been destroyed.
Now we just store the acid in glass bottles.
Although some chemists prefer polypropylene bottles because there is less danger of them breaking if they are dropped.
I guess I'm old school preferring my sulfuric acid in glass.
Let me clean the surface, because then we can label them.
And there is our high grade 98% concentrated sulfuric acid distilled from drain cleaner.
To test the acid we pour some it on tissue and we can see it decompose and char.
And that was the purification of sulfuric acid by distillation.
I like this improved method because it avoids hard to find high temperature grease
and substitutes it with comparatively easy to find PTFE pipe threading tape.
The tape also makes it very easy to take the joints apart when youíre done.
This improved method using the ceramic hotplate stirrer also greatly reduces dangerous bumping that boiling sulfuric acid is notorious for.
The big drawback of this improved method is that you need to get a high temperature ceramic hotplate stirrer which can be very expensive.
But because of how useful they are for other experiments, I feel the cost is justified in the context of a larger laboratory.
Anyway, Iím going to use this purified acid in upcoming videos on electroplating and analytical chemistry.
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