jsc - 8-1-2015 at 13:47
I am interested in drying some calcium chloride which I have in the form of small white pellets of the type used for sidewalk de-icing.
I want to weigh them as inputs to a reaction, but any absorbed water will invalidate the weight, so I need to dry the pellets completely.
Note that de-icing pellets are much different than the hard calcium chloride "chips" that you might have used as a drying agent. The pellets are soft
and crumbly and about the size of those little silver cake decorating balls.
My main choices for drying are (A) a microwave oven, and (B) a toaster oven (used for chemistry only). Should I prefer one or the other.
Hellafunt - 8-1-2015 at 14:01
just in case anyone cares, the silver cake decorating balls are called dragees, pronounced drah-zhays . im a baker! and they are made in an
interesting way, the same as pills are made
[Edited on 8-1-2015 by Hellafunt]
chemrox - 8-1-2015 at 17:33
You can remove the water by heating the material until the water comes off. Depending on how much you need I would use a ceramic casserole over a
flame and stir until no more water is evolved. If you searched you'd probably find this somewhere...(utsf?)
aga - 9-1-2015 at 15:40
Really truly anhydrous CaCl2 is difficult to obtain, as it is so hygroscopic it deliquesces.
Just heat it a lot, until it looks pretty dry, then stuff it in an airtight container as soon as possible.
[Edited on 9-1-2015 by aga]
subsecret - 9-1-2015 at 20:06
Whether in a toaster oven or microwave, be sure to open the door every few minutes (may be excessive) to let the moisture out.
hissingnoise - 10-1-2015 at 04:54
I tried drying the stuff once ─ and got a hard, almost unbreakable plaster for my trouble . . .
subsecret - 10-1-2015 at 06:22
I assume you spread it into a layer? How thick was it?
[Edited on 10-1-2015 by Awesomeness]
Mabus - 10-1-2015 at 08:05
Would vacuum drying work better?
aga - 10-1-2015 at 11:22
The first time i dried CaCl2 i simply got annoyed that it would not dry in the beaker, so dumped the entire beaker contents directly onto
the hotplate.
It spread itself to maybe 3mm thick, sizzled and bubbled, and became a white powdery cake that stuck rather well to the hotplate.
Scraping and moving the mass all the time that it is on the hotplate prevents it becoming a solid slab.
An SM member said their method was to heat it until the Calcium Chloride melts = 772 C !
Clearly that would remove all of the water, yet is more challenging, practically speaking.
Mabus - 11-1-2015 at 03:48
When first dried some CaCl<sub>2</sub>, I partially melted it, though it was accidental, I didn't thought I could reach such a high
temperature with a made-up wood stove and air.
AJKOER - 11-1-2015 at 11:41
Some comments from Atomistry http://calcium.atomistry.com/calcium_chloride.htm To quote:
"It can be prepared by neutralisation of calcium carbonate or oxide with hydrochloric acid and evaporation to dryness. To obtain the anhydrous salt
the residue must be fused, but as the action of water vapour tends to decompose it and make it alkaline, hydrochloric acid gas followed by nitrogen
must be passed over it. "
In other words, just heating CaCl2.xH2O, absence HCl gas, likely forms significant amounts of CaO.CaCl2. This statement is in line with Atomistry on
Calcium oxychloride http://calcium.atomistry.com/calcium_oxychloride.html . To quote:
"On fusing calcium chloride in moist air it becomes basic, due to the formation of an oxysalt, CaCl2.CaO. On prolonged heating it forms calcium
oxide."
Also, to quote:
"The formula of the partially dehydrated salt has been given as CaCl2.3CaO.3H2O, and also as CaCl2.2CaO.H2O. Schreinemakers and his colleagues,
however, have carefully studied the system, CaO: CaCl2: H2O, under varying conditions of temperature and concentration, and their results indicate the
existence of the following compounds: at 10° and 25° C., CaCl2.3CaO.16H2O and CaCl2.CaO.2H2O; at 50° C., CaCl2.CaO.2H2O and CaCl2.CaO.3H2O; and
also CaCl2.4CaO.14H2O. "
aga - 11-1-2015 at 15:45
Interesting AJ !
Thanks for the links.