In our previous video we showed you how to prepare potassium iodate and we tried to use
potassium perchlorate to see if it was possible to prepare potassium iodate in the same way,
but it failed.
So today we'll prepare potassium iodate in a proper way.
First a tour of the apparatus we're using.
This our chlorine generation flask, which has two necks.
It's a bit dirty so we're hoping this will help clean it a bit.
On top of this is an addition funnel so we can add a liquid to the flask.
This smaller neck has some adapters fitted into it, and some anhydrous calcium chloride
granules which are held in place using some loosely packed cotton wool.
These will dry the chlorine gas and help remove any acid aerosol created.
Coming off these adapters we have a plastic tube, which loops back down and attaches to
a glass tube with a nice seal using some PDFE plumber's tape.
This then leads down into a conical flask.
This is a flask which is capable of holding around 150 mils of liquid.
And this is set up on a hot plate stirrer, with a magnetic stir bar, and also a thermometer
attached so we can measure the temperature.
Okay there we go.
If you want to improvise this differently then the hot plate is essential, as if the
ability to very slowly add the acid into the chlorine generator flask.
Let's set up our chlorine generator.
First, we're going to use 18 grams of potassium permanganate crystals.
This will give us approximately a 2.5 molar excess of chlorine compared to what we need
in theory, but as you'll see this seems to work best.
Let's get the permanganate crystals into the flask.
And for the other part of our chlorine generator.
Here's 70 mils of concentrated 36.7.
Check that the funnel tap is closed.
Then add this to the addition funnel.
Now we'll make up our reaction solution.
Here we have 20 grams of potassium hydroxide.
This is a 3 times molar equivalent compared to the iodate that we'll be using.
To begin with we're going to dissolve this in 100 mils of water.
And we're going to dissolve this in 100 mils of water.
Okay, we've got a nice warm solution of potassium hydroxide here.
Now we're going to pour this carefully into the conical flask.
Here we go.
Now we're going to start stirring.
And we're going to switch on the heat so that this solution heats up.
It's around 40 degrees C now.
But we need it to be above 90 degrees.
Okay, last but not least, our main reactant.
This is 25 grams of the potassium iodate we prepared in the previous video.
It's turned slightly yellow in color, possibly due to a small amount of oxidation.
But it's otherwise quite pure.
We add this to the potassium hydroxide solution in the conical flask.
Note that not all of the iodate is going to dissolve.
I'm going to add a little bit of potassium hydroxide here.
Until the temperature gets very high.
All in now.
And we'll keep stirring and heating this now until we've got a temperature of around 90
degrees C.
Okay, here we go.
So at this point we're ready to start bubbling chlorine through the mixture.
We're just going to add a little more water so we can get most of the solid in solution.
A little bit won't do.
It's going to dissolve.
But this is okay.
It will later on.
So very slowly, we start the acid dripping into the flask onto the permanganate crystals.
Nice and slow to begin with.
And we've got bubbles of air coming through the liquid to begin with as it's displaced
by the chlorine gas produced.
And we're ready to go.
The chlorine has it's produced should dissolve very readily in the solution.
So we couldn't detect any being emitted from the top of the flask.
You can begin to see the green color of the chlorine gas in the generation flask now.
Okay.
So we're just going to leave this now and let the chlorine generate and bubble through
slowly.
The makeshift drying tube seems to be working well.
About a third of the way through the acid addition, we noticed that the residual potassium
iodate solid in the flask was dissolving.
And pretty soon the liquid in the flask become clear and colorless.
Although our product, potassium periodate is not very soluble in water, it does form
an intermediate soluble salt in conjunction with the excess potassium hydroxide.
About half way now.
And now we're starting to get a solid forming again in the reaction flask.
And pretty soon the mixture turned opaque again as the product precipitates.
Our mixture also turned a slightly pink color.
We're not sure why, but probably due to some permanganate getting in from somewhere.
Pretty soon our product starts to build up on the bottom of the flask.
The temperature is still very low.
And now we're finished with acid addition.
The total addition took about an hour in total, but we're going to leave the generation flask
for about 15 minutes now to make sure that all the chlorine has been generated.
The product has precipitated nicely.
And it's only now that we start to detect a little bit of chlorine gas being given off
by the reaction mixture.
And it's only now that we start to detect a little bit of chlorine gas being given off
by the reaction mixture.
Once gas generation is complete, we dismantled this part of the apparatus and then allowed
the flask containing our product to cool down.
Let's check the pH.
We want the solution to be neutral or even slightly acidic.
It's strongly bleaching so it's hard to tell, but there's no sign of an alkali coloration
so that's okay.
If the solution is alkaline, then you'll need to add hot water.
to it carefully in order to precipitate the rest of your product okay the
solution is now at room temperature so let's filter the product
we get it nice and dry and then wash thoroughly with some cold water to
release the impurities
here's our final product as dry as we can get it on the pump it's a fluffy
looking but quite dense very slightly off-white solid
and we've got 27 minutes left to go
grams of potassium periodate here.
In theory the 100% yield from this reaction is 26.8 grams, so it's probably slightly
damp, but we're got a pretty much quantitative yield of product.
Potassium iodate can be used as an oxidant in organic chemistry, and so we're hoping
to see if we can use it for this in the future.
One note, this reaction does work for sodium iodate, but is a little different and the
not the exact same compound.
For more information you'll need to look this up and do some research on orthoperiodates.
That's all for this video.
Thanks for watching and stay tuned.