Sciencemadness Discussion Board - Preparation of Potassium Antimony Tartrate

Preparation of Potassium Antimony Tartrate

Texium - 23-7-2015 at 08:19

Yesterday I prepared the double salt potassium antimony tartrate. The following is a write-up of my procedure.

2 KC₄H₅O₆ + Sb₂O₃ –> K₂Sb₂(C₄H₂O₆)₂ • 3 H₂O

18.82 grams of potassium bitartrate (cream of tartar) and 14.58 grams of pottery grade antimony trioxide were added to a 500 mL long necked Florence flask (2:1 molar ratio, based on the formula of the double salt since I had nothing else to go on). To this, a magnetic stir bar and approximately 250 mL of distilled water were added. Then, the flask was placed on a hot plate and brought to a boil while stirring vigorously. After being brought to a boil, the slurry was allowed to reflux for 30 minutes. After 30 minutes, most of the solids had dissolved, and this was especially apparent after turning off the stirrer, and allowing the now reduced volume of solids to settle to the bottom of the flask. The solution was then filtered while hot to remove any unreacted reagents that hadn't dissolved (heating the funnel is not necessary as long as it is not allowed to cool down too much before filtering, as crystallization of this compound appears to be quite slow), and then transferred to a 600 mL beaker and placed in the freezer to crystallize.

After about an hour and a half in the freezer, as the water in the beaker was beginning to freeze, a crop of pure white, glittery, triangular crystals weighing 16.43 grams was recovered. A second group of crystals from the remaining solution is being crystallized now, albeit in the fridge at a slower rate. The first picture shows the first crystals that were formed, making it easy to see they're neat triangular shape. The second picture shows the full 16.43 grams. In a matter of time, I will post an update with a picture of the second batch of crystals.

[Edited on 7-23-2015 by zts16]

Oscilllator - 23-7-2015 at 17:38

Very nice. I'm always amazed when a reaction comes up where a metal oxide somehow manages to get into solution without the use of strong acids or bases.
Was the cream of tartar you used supermarket grade? If so, you might want to look out for anticaking agents and the like.

Texium - 23-7-2015 at 17:55

Yes, it was from the grocery store. If there was anything in there other than potassium bitartrate, it was most likely removed by either the recrystallization or the filtration, as the crystals appear to be uniform and pure. The bottle didn't list ingredients though, so I don't know for sure.

UC235 - 23-7-2015 at 18:09

Quote: Originally posted by zts16

Yes, it was from the grocery store. If there was anything in there other than potassium bitartrate, it was most likely removed by either the recrystallization or the filtration, as the crystals appear to be uniform and pure. The bottle didn't list ingredients though, so I don't know for sure.

I don't believe that "cream of tartar" typically has any anticake added. The solid is pretty nonhygroscopic and from what I remember of trying to make rochelle salt with it, did not leave any solids after solution. It is also notably used as an anticake itself.

It's a waste product from the grape juice and wine industry. Chilling the juice causes it to crystallize out, and potassium bicarbonate may be added to force precipitation of additional bitartrate in order to reduce acidity.

It's pretty easy to recrystallize as well from boiling water, though you will need a large solution volume since only about 6g will dissolve in 100ml at boiling. You'll recover about 90% of that on cooling.

j_sum1 - 23-7-2015 at 19:02

I don't have any antimony oxide, but I'd really like to try this. I think I'll attempt an analogue with Cr2O3.

I think also you should upload some nice crystal pix to Wikipedia. The article has some pictures but not the beautiful triagular crystals that you have found.
https://en.wikipedia.org/wiki/Antimony_potassium_tartrate

Boffis - 27-7-2015 at 15:56

Nice experiment! I like those triangular crystals too! Are they actually tetrahedron like Schlipp's salt (Na3SbS4)?

Texium - 6-9-2015 at 08:25

No, they aren't tetrahedral, they're actually flat, triangular plates. I haven't ever seen any crystals quite like these.

Also, I just made a page for it on the wiki: http://www.sciencemadness.org/smwiki/index.php/Potassium_ant...
As you can see, it's still lacking a lot of information, but I think it's already more useful than the Wikipedia page, from a home chemist's perspective at least. I would have included more about chemical properties and other things, but there really isn't a whole lot out there about it chemistry wise.

Also, I noticed that according to the structure and formula, the tartrates in this compound are not normal tartrate anions, C₄H₄O₆<sup>2-</sup>, but rather C₄H₂O₆<sup>4-</sup> with the two hydroxyl groups being deprotonated. I thought this seemed rather interesting.

[Edited on 9-6-2015 by zts16]