sodium metal to create a mixed alkali cyanide salt.

Today we're going to have another go at preparing cyanide salts, only this time in a slightly

different and more OTC way.

Before we get started, the usual warning.

Don't mess around with cyanide salts because they will easily harm or even kill you very

rapidly if you ingest them.

They are however very useful for lots of organic chemistry.

And we've featured them in our previous videos.

Let's do it.

Here's our first reactant.

As before we're using potassium ferrocyanide as our source of cyanide ions.

And here's 8 grams of anhydrous salt.

If you have crystals in the dihydrate you can heat these in an oven at 150 degrees C

for a few hours and stir them around occasionally to get the fine pale yellow anhydrous powder.

Note that in ferrocyanides the cyanide ions are bound very tightly to the central iron

atom forming the ferrocyanide complex.

This strong binding makes them relatively non-toxic.

Okay now for our second reactant.

Instead of sodium metal, in this preparation we're going to use an alkali carbonate salt.

In this case 3 grams of anhydrous potassium carbonate, which is a stoichiometric salt.

The first thing we're going to do is mix these two dry powdered reactants together

very well.

And here we are.

Well mixed together and any lumps broken up carefully.

We're doing the reaction on a small scale.

So for the heating part we're just going to mix these two dry powdered reactants together

and we're just going to use this small porcelain crucible.

It's important that you've got a lid because we'll want to keep air out during the heating.

Too much air and the oxygen will oxidize our hot cyanide salt into cyanate as it's produced.

So let's get our reaction mixture into the dry crucible.

Here we go.

Now we'll use the spatula and pack it down so that's it's nice and compact.

Better heat transfer.

Let's put the lid on the crucible.

And now it's rock and roll time.

We're going to heat the mixture on our regular kitchen burner.

Don't worry it's our spare kitchen so there's no food around here apart from the occasional

lab chocolate cake.

The reaction needs to get pretty hot.

So we're hoping that we've got enough heat here to make this work.

On the kitchen burner this might take a little while.

About 4 minutes of heating.

Let's have a quick look.

Not a lot of difference.

Some brown color appearing around the sides.

We'll keep heating.

While it's heating, let's have a quick look at what's happening here.

Here's the overall reaction.

It's a little unusual.

The effect of the heat causes the ferrocyanide to decompose.

In the presence of potassium carbonate we get a reaction producing carbon dioxide, potassium

cyanide, and a small amount of potassium cyanate.

The iron from the ferrocyanide ends up as iron metal.

Note that the iron from the ferrocyanide ends up as iron metal.

The iron has effectively been reduced.

About 10 minutes in now.

So let's have a peek again.

We've got a black color starting to form.

This is the reaction starting.

We're going to leave this for 10 minutes now and then we'll come back and have a look again.

Let's fast forward.

This is 20 minutes into heating.

The reaction is consistent.

Continuing.

We've got to keep heating now until the mixture actually melts.

Okay, another 10 minutes.

30 minutes of heating in total now.

The mixture is completely black.

But no sign of melting yet.

At least at the surface.

So another 15 minutes of heating.

45 minutes in total.

And we now got a melt forming in the crucible.

The bottom is red hot and glowing.

Looking pretty good.

So we'll stop here.

Pure potassium cyanide melts at over 630 degrees C.

The cyanate at only 315 degrees.

So the mixture is bound to melt somewhere in between.

And our crucible temperature isn't unrealistic.

we've covered the crucible up again and we'll let it cool right down to room

temperature here's the crucible and contents after cooling you can see a

rusty brown color in there where some of the iron has oxidized first thing we're

going to do now is add just a little bit of water around 10 mils and try to break

up the solids

after a few minutes of gently scraping the cake of solid comes loose in the

crucible

so now we transfer into a small beaker

and we're going to add

a little hot water and stirred well until all the lumps have dissolved

leaving only the fine black precipitate

we're there now with all the large lumps dissolved the total volume now is around

20 mils we're now going to filter off the black solids and leave a solution

remaining with our product in to do this we're going to use some gold school

filter technology because we are only dealing with a small amount of liquid

we're pretty much there now

we're pretty much there now

we're pretty much there now

here's our filtrate it's only a very pale yellow color which is great because

it means that the ferrocyanide has all reacted and it's got that characteristic

musty weird aroma that solutions have alkalized cyanide salts have only

subtly like almonds but remember that not everyone can smell that particular

infamous characteristic well this probably also has potassium carbonate

and potassium cyanate in it as well but it's a pretty good solution for your

solution so we're going to first chill it down and see if we can get any solid to crystallize

out in the previous video we used ethanol to precipitate the cyanide salt but in this

case this process will also precipitate the cyanate as well while that's chilling down

in the freezer here's some water in a beaker we'll add a little of the back precipitate

that we recovered from the filtering process and stir it around

here we go okay let's use a magnetic spur bar and see if we can demonstrate

that it's actually finely powdered iron that has been produced

definitely a magnetic response as you can see

back to our filtrate chilling down after about 30 minutes we've definitely got

some fine crystal from this fertilizer

in the bottom so we'll keep chilling a bit longer and see if we get any more

and here we go after another 30 minutes in the freezer definitely some crystals

in there let's filter these off this time using a vacuum and see what we've

got

here we go about 1.3 grams of very pale yellow clumpy crystalline solid

cyanide salts are very water-soluble so this is actually not bad at all the

cyanate and carbonate are much more water-soluble at this temperature so we

think there's a good chance that this contains a high proportion of potassium

cyanide

it definitely gives all the right chemical reactions in some tests which

we'll come on to in a moment

as far as yield goes if it's pure cyanide salt then that's an 18% recovery

but most of the product is still in the liquid filtrate along with other

inorganic salts as well

well this process seems to work quite well and it's definitely a lot more OTC

than using sodium metal but how good is the product

so let's look at the results

let's look at some qualitative tests for cyanide to do this we'll use the

aqueous filtrate which in theory contains most of the product the first

test you've seen before because we did it in the previous cyanide video let's

add some saturated copper sulfate solution to the filtrate

dark-colored copper to cyanide is produced which rapidly decomposes the

forming cyanogen gas there's also a green color so this shows there's

definitely some carbonate remaining in the filtrate as well okay so that's one

test but let's do this again now with a slight variation here's our copper

sulfate solution again now we'll add some sodium hydrogen sulfite this will

form the yellow green colored complex and solution with the copper

and now we'll add the filtrate containing our suspected potassium

cyanide to this and see what happens this time this time we've mostly got a

white precipitate forming this is copper one cyanide being formed as an

insoluble precipitate there's a slight brown color due to some copper to

cyanide forming transiently before it decomposes copper one cyanide is very

interesting because it is a useful reagent in organic chemistry we may be

preparing and using it again in a future video well so far that series of

reactions and color changes is definitely consistent with there being

alkalized cyanide present in the solution let's try the classic test next

here's a bit more of the filtrate

and here's an aqueous solution containing the

mixture of iron chloride and iron to sulfate

interesting at first there's a dense green precipitate of what looks like

iron carbonates but the second there is an excess of iron salts a deep intense

blue color appears this is the famous russian blood

a complex molecule comprising iron and cyanide ions.

Well, no doubt, there's some potassium carbonate in the mixture,

but there's also a lot of cyanide as well as you can see from the intense coloration.

So this method is a success.

We still don't know exactly how much cyanide it produces and how pure our crystalline product is,

but it's giving qualitative tests.

We'll have to come up with a quantitative way to measure this,

possibly by making copper cyanide and then weighing it.

Please stay safe with cyanide, and stay tuned for more reactions.

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