Lion850
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Report on attempt to make cerium iodide
Reading up online I learned that cerium (iv) iodide does not seem to exist, and that cerium (iii) iodide can either be a dehydrate which is yellow and
decompose in moist air or a nonahydrate which is white to reddish.
First on test tube scale I tried to mix some lead iodide with cerium (iv) sulphate, hoping that CeI4 would be formed which would then decompose to
CeI3 and elemental I2 (similar to the behaviour of copper iodide when made by double displacement). But what happened was that I got a ppt of lead
sulfate as expected but ALL the iodine seemed to appear as elemental iodine, testing the remaining solution siphoned off with a pipette with a lead
nitrate solution showed no sign of any iodide.
I then added drops of hydrogen peroxide to a yellow solution of cerium (iv) sulfate until it cleared up. I then repeated the double displacement with
lead iodide with this clear solution which should have contained cerium (iii) sulfate. With the cerium sulfate in slight excess by my estimation.
This mix of 4.5g Ce(SO4)2 input prior to changing to Ce2(SO4)3 was stirred with 8g PbI2 in 250ml water overnight. The next morning the solution was a
lovely wine red color with very fine very pale yellow ppt (I saw before when doing erbium and neodymium that the precipitated lead sulfate is always
colored very slightly yellow). I was quite excited at this point as I though the red color must be the nonahydrate.
After filtering the solution was boiled down. To my disappointment the color faded to slight orange as it heated and then even more as it boiled down.
By the time it was around 100ml it was completely clear, but as 50ml it was pale yellow. At 30ml the solution was first filtered hot to get out any
unreacted cerium sulfate (very low solubility in boiling water) and then cold to filter out the few flakes of lead iodide that appeared.
This 30ml was then put into the desiccator over sodium hydroxide and high vacuum. 12 hours later there was a off-yellow paste left as far as I could
see from the glass, vacuum was still good. 18 hours later it was much drier....but had gone dark brown.
The crucible was removed from the desiccator, and the contents immediately continually fumed slightly and just about all the remaining yellow turned
dark brown quickly. 5g of this mess was eventually recovered in a vial. I was not expecting it to decompose so fast in the air.
So a failure, but interesting as always. The initial red solution intrigues me; was this the nonahydrate and then why did it so easily lose its color?
I would like to try this double displacement again but in a much smaller amount of water, and try with barium iodide which has much better solubility
than lead iodide. And then place the red solution straight into the desiccator without any heating. But to do this I will first have to make barium
iodide.
Reaction iodine direct with cerium metal in a solvent will also be worth trying....but I do not have cerium metal.
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Lion850
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I had another go to make the nonahydrate. I reacted iodine with barium hydroxide to make barium iodate and barium iodide. This went quite well as far
as I can see, the expected weight of iodine reacted with the barium hydroxide, and slight excess resulted in the solution remaining pale yellow until
a few more grains of barium hydroxide was added. The solution was slowly boiled down and the insoluble barium iodate filtered off (this was later
weighed when dry and found to be within 10% of the expected weight).
This left me with a solution of barium iodide and this was reacted with cerium (iii) sulfate. A ppt of barium sulfate was obtained and a wine red
solution which I assumed was CeI3.9H2O which is said to be reddish. The red solution was decanted off and filtered and this was then placed straight
in the desiccator over NaOH under vacuum.
It dried out in a few days, and I was left with some 5g of brown-yellowish crystals. Some specs of red. I was expecting a much higher yield of around
12g, not sure what happened to the rest, but the precipitated barium sulphate has a yellow tinge and I suspect more iodide could have been washed out.
I did not wash it as I did not want to end up with a big volume to evaporate. Although the barium sulfate, once dried, was also not far off the
expected weight.
The product dissolves easily in water and then gives a yellow ppt when tested with lead nitrate. It does not fume in moist air, unlike my previous
(probably dehydrated) product described above. It is also not obviously immediately hygroscopic.
I stored it in a clear vial to see how long it lasts, and after 3 days it has discolored to a dark color due to iodine release.
This concludes my attempts with cerium iodide for now.
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CharlieA
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Just out of curiosity, in your original post, you refer to "reading online'". Do you have references to any specific papers or articles from which you
drew your experimental procedures? Your write-ups are very well written
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Lion850
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CharlieA - generally sites like wikipedia and atomistry.com will be the places to find information on compounds as well as the Sciencemadness library
and discussions. And of course Google takes one to a zillion places, some useful and some not.
Plus looking at YouTube videos, Poormanschemist on YouTube and Facebook is always keen to help and pass on his experience.
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