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woelen
Super Administrator
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Registered: 20-8-2005
Location: Netherlands
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Mood: interested
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I tried recrystallizing my solid material, but this failed.
I took the pale green material, left over from my experiments of last week. The material still was a dry pale green powder, it had not become humid in
the last week, despite it being stored in contact with air.
I added a small amount of distilled water to the solid and carefully heated. The material did dissolve, but I also observed very strong foaming.
Really fine foam, not bubbling, but fine foam, like the foam you get when shampooing your hair. The liquid also did not become green like aqueous
nickel(II), but it turned mustard-like (yellow/brown with a hint of green). The liquid became fairly clear (some opalescence remained and also a few
larger grains remained floating around), but the compound I had was not sorbate anymore. I tested this by adding a little amount of cold dilute
sulfuric acid to a cooled down small portion of the quite concentrated mustard-colored liquid. When this was done, the liquid become really clear,
while keeping its mustard color. Sorbates form a white precipitate with acids, because of the low solubility of sorbic acid in cold water, so this
liquid did not contain sorbate anymore in appreciate amounts.
While heating the liquid with the solid impure nickel sorbate, I also noted a strong smell. It was a little bit like the smell of acetaldehyde (the
smell you get when oxidizing an acidic solution of ethanol with a relatively mild oxidant like dichromate), but a little more musty. Apparently, the
heating to near boiling decomposes the sorbate ion and some nickel complex is formed with a mustard color.
As a counter experiment I dissolved some potassium sorbate in quite a large volume of acid. This dissolves extremely well, giving a clear colorless
solution. When a little dilute sulfuric acid is added to this solution, you get a white precipitate. This white precipitate can be dissolved, when the
solution is heated to near boiling. While doing so, I again observed formation of very fine foam and the solution started to smell like acetaldehyde.
I also tested by adding a few drops of a solution of K2Cr2O7 to the boilingly hot solution of sorbic acid in excess sulfuric acid. The dichromate is
not reduced quickly, one needs to boil the liquid for several minutes before all dichromate is converted to some green chromium(III) complex.
I get the impression that sorbate is not very stable at higher temperatures and that purification of the nickel(II) sorbate, produced from
concentrated solutions, hardly is possible.
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Amos
International Hazard
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This thread has been a fun read, but I facepalmed at every precipitate that ended up having a less desirable color after heating/drying.
Lion, might you try more washing, followed vacuum filtering or at least squeezing these precipitates totally dry, then drying them at room temperature
in a desiccator? This group of salts definitely appear to be heat-sensitive. I'd love to see the chromium, nickel, and iron compounds survive the
workups.
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