At some point you may accumulate a stash of silver iodide.
This is a by-product of making nitrolethane.
Today we're going to show you how you can convert this back to very useful elemental iodine and silver metal.
But we'll warn you now, it's not simple.
And there's lots of toxic stuff involved so you really need to make sure you've got good ventilation handy.
We're starting with 50 grams of solid dry silver iodide.
This is a great solid as you can see.
Crush this up so it's as fine a powder as you can get with no lumps in it.
This will help with recovery yields.
You'll need a 250 ml beaker equipped with a large magnetic stir bar for the first part of this process.
First of all we're going to mix up a fresh batch of aqua retia.
This is a mixture of concentrated nitric and hydrochloric acids.
Here we've got around 30 ml of 68% concentrated nitric acid.
Make sure you have a little bit of concentrated nitric acid saved for cleaning purposes later on, you will need it.
Let's first get this into the beaker.
And now we've measured out 90 ml of concentrated hydrochloric acid.
This is a three to one ratio of acids in terms of volume, which is the classic recipe for making aqua retia.
We add this to the beaker containing the nitric acid.
The mixture of acids slowly turns a yellow and then a golden color.
It also gives off some pretty nasty fumes to get your ventilation going and cover the beaker up as well.
What is happening now is a reaction between the acids producing compounds such as nitrosyl chloride in solution.
Some chlorine gas is also produced as a decomposition product.
If you need to make this, always make it fresh because it won't last long and will decompose slowly.
It's also very toxic and corrosive to take care.
After about 10 minutes the liquid develops its characteristic orange golden color.
So now we're ready.
We're going to add the silver iodide to the aqua regio slowly.
There's a little bit of heat produced, but not too much, and some bubbling of the liquid as a reaction takes place.
What is happening is a reaction which is converting the silver iodide into silver chloride.
At the same time,
the iodine is being oxidized and is forming a variety of compounds in solution including chlorine iodide and iodic acid.
You can see a yellow colored solid.
This is our silver chloride being formed.
Once we've added all the silver iodide to the mixture,
we're going to leave this stirring for an hour so that it has a chance to react completely.
Stopping stirring for a second, you can see the dark brown color of the liquid.
Stopping stirring for a second, you can see the dark brown color of the liquid.
iodine you'll find that the fumes of chlorine and nitrogen oxides die down
after a few minutes but it's worth keeping the mixture covered anyway
because the vapors are toxic and extremely corrosive
okay here we are one hour later the red liquid and the yellow colored
precipitate at the bottom you don't want to filter this as it is because the
so we'll dilute the mixture first with some water to reduce the fumes here we've
got 70 mils of cold water add this carefully to the mixture don't add too
much or you'll start to precipitate elemental iodine which we want to keep
in solution for the moment okay it's time to filter
wash the beaker out with another 100 mils of cold water
and then another 100 mils to thoroughly wash the precipitate
and then get it reasonably dry
here's our silver chloride it's quite damp still so we didn't bother to weigh
it we'll come back to this later on to show you how to recover the silver first
we'll work up the filtrate which contains the iodine which is also a
valuable product that we want to recycle the filtrate is now diluted with the
washing water and you can already see some black crystals of iodine forming we
transfer this to a large beaker
the iodine chloride and other iodine compounds in here are stable in acid
solution so we'll first dilute the mixture down some more to see if we can
decompose them here's 250 mils of cold water we let this rest for two hours in
the fridge as the decomposition does take a little while to complete
and now let's filter off our first batch of iodine
we wash the beaker with 50 mils of cold water then dried our initial batch on
the pump
you
, by further diluting the filtrate and adding 20 grams of solid sodium
hydroxide and leaving overnight to rest we got another batch of iodine forming
the original process we're working from suggests complete neutralization of the
acid in order to recover the iodide but we find that this isn't necessary if you
dilute the mixture right down and partially neutralize with solid sodium
hydroxide
here's our second batch
and we transfer the dried solid iodine to our recovered iodine bottle for future
use
in total we recovered 21 grams of solid iodine this is a 78% recovery yield from
the starting silver iodide which isn't bad
and it's quite a simple process
however now we have to deal with the silver chloride that we've recovered
here's our lumpy silver chloride precipitate which turns dark on exposure
to light
and here's 250 mils of 15% aqueous ammonia solution silver chloride will
dissolve in aqueous ammonia to form a soluble silver ammonia complex
don't be tempted to use concentrated ammonia as this can lead to the highly
explosive silver nitride
being formed
ok let's add some of the silver chloride to the ammonia solution the mixture
turns to slightly white color and the solid dissolve slowly
let's get this all in and we'll stir the mixture for about 30 minutes to get
the solid to dissolve
yeah
yeah
a small amount of the solid won't dissolve even on adding another 50 mils
of ammonia solution we assume this is residual unreacted silver iodide from the
first step
so we decant off the silver solution
ok in order to convert this to silver metal we now need a reducing agent one
which doesn't react with the alpha-ali ammonia and which is strong enough to
create a precipitate rather than a decrease in acidity this is only been described as a proof to understand that silver iodide is actually the best solution for the oxygen production process.
silver mirror on our glassware. So we're making up a nice strong solution of sodium bisulfute,
and we're going to use this to make some sodium diphenite which works well.
Check out our previous video for full details of how to make this.
But you add finely powdered zinc metal to a strong sodium bisulfite solution.
You need to cool the mixture a bit as the reaction progresses.
The reaction generates zinc hydroxide as a great precipitate and the aqueous solution contains sodium diphenite.
So filter off the solution when the reaction is complete and you can use this to reduce the silver ammonia complex.
Here's our diphenite solution. It's orange because we also used it to clean the glass
center that we used for the iodine filtration. Let's add to our silver ammonia solution.
The black precipitate formed is metallic silver. Formed in very fine suspension as the silver compound is reduced to the metal by the sodium diphenite.
We found that a solution of diphenite prepared from 40 grams of sodium bisulfite was sufficient to reduce all the silver.
And here we go. You can see the silver clumping together now and forming a dark gray dense precipitate.
it on the bottom.
Time to filter once again.
The filtrate should be quite clear and colorless.
Wash well with water.
Vent with 20 mils of absolute ethanol to dry the product.
And here we go.
A dark gray dry powder of precipitated silver metal.
We collected 19.9 grams which corresponds to an 87% recovery yield.
We've also got a small amount of undissolved silver iodide left which we can save for the
next time we do this.
But it's a pain in the ass so we don't do this too often.
You can use other reducing agents such as hydrazine or even glucose sugar.
The problem though is that they tend to generate a silver mirror all over the glassware, which
is a mess.
You can experiment though.
And here's our two products.
Silver metal and solid iodine.
Two individual elements recovered from silver iodide.
A molecule of both these atoms.
Which is kind of neat.