jsc
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Drying calcium chloride
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.
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Hellafunt
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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]
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chemrox
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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?)
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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aga
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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]
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subsecret
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Whether in a toaster oven or microwave, be sure to open the door every few minutes (may be excessive) to let the moisture out.
Fear is what you get when caution wasn't enough.
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hissingnoise
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I tried drying the stuff once ─ and got a hard, almost unbreakable plaster for my trouble . . .
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subsecret
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I assume you spread it into a layer? How thick was it?
[Edited on 10-1-2015 by Awesomeness]
Fear is what you get when caution wasn't enough.
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Mabus
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Would vacuum drying work better?
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aga
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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.
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Mabus
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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.
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AJKOER
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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. "
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aga
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Interesting AJ !
Thanks for the links.
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chloric1
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Maybe heating dry with ammonium chloride.
Fellow molecular manipulator
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macckone
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in order to avoid a cake you want to heat very slowly from 25 to 50C and then up to 165C and hold for 2 hours then slowly to 180C and then to 250C
hold for two hours and then slowly to 265 or 270C. The last step is outside of the range of many toaster ovens, most don't go over 230C (450F). the
trick is to keep it below the point where it rapidly releases water. Those points are 30C, 45C, 175C and 260C. You can drive off water below those
points but it takes time.
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Precipitates
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I produced 100 g or so of some mostly anhydrous calcium chloride the other day.
I boiled a calcium chloride solution (from calcium hydroxide + hydrochloric acid) until about half of the calcium chloride had precipitated (suspected
as the dihydrate), and then put it in the fridge (a relatively desiccating environment), as it was getting late.
Overnight the hexahydrate formed, which "melted" upon heating, although it was rather the calcium chloride dissolving in its own water of
crystallisation.
As the solution boiled dry, I stirred to prevent the calcium chloride sticking and forming large chunks - although some small hard balls did form.
These were mortar and pestled back into a powder.
This powder was then heated until it stopped crackling (over an hour or so), to produce a mostly fine, slightly off-white and very hygroscopic powder.
It was stored immediately in an air-tight container whilst still hot.
This procedure worked, but was very harsh on my glass jug, which ultimately cracked (I should have allowed it to cool more slowly by leaving it on the
hotplate).
RIP PYREX jug 
Note the jug looks clean due to the strongly deliquescent nature of the calcium chloride.
[Edited on 13-8-2024 by Precipitates]
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yobbo II
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Some info on CaCl2 attached.
<html>
<table border=3> <th colspan=4 bgcolor=dodgerblue> Density of Calcium Chloride solutions in g/cm^3 at 20C</th>
<tr><td>Mass %</td><td>Moles/l</td><td>Grams/l</td><td>Density</td></tr>
<tr bgcolor=black><td colspan=4></td></tr>
<tr><td>10%</td><td>0.976</td><td>108.3</td><td>1.0835</td></tr>
<tr><td>20%</td><td>2.122</td><td>235.5</td><td> 1.1775</td></tr>
<tr><td>30%</td><td>3.464</td><td>384.5</td><td>1.2816</td></tr>
<tr><td>40%</td><td>5.03</td><td>558.3</td><td>1.3957</td></tr>
<tr><td colspan=4>From The Engineering Toolbox on the web
</table>
</html>
Can't do HTML how do you do HTML?
Yob
Attachment: ca_cl.pdf (589kB)
This file has been downloaded 104 times
[Edited on 14-8-2024 by yobbo II]
[Edited on 14-8-2024 by yobbo II]
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SplendidAcylation
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Quote: Originally posted by Precipitates  | I produced 100 g or so of some mostly anhydrous calcium chloride the other day.
I boiled a calcium chloride solution (from calcium hydroxide + hydrochloric acid) until about half of the calcium chloride had precipitated (suspected
as the dihydrate), and then put it in the fridge (a relatively desiccating environment), as it was getting late.
Overnight the hexahydrate formed, which "melted" upon heating, although it was rather the calcium chloride dissolving in its own water of
crystallisation.
As the solution boiled dry, I stirred to prevent the calcium chloride sticking and forming large chunks - although some small hard balls did form.
These were mortar and pestled back into a powder.
This powder was then heated until it stopped crackling (over an hour or so), to produce a mostly fine, slightly off-white and very hygroscopic powder.
It was stored immediately in an air-tight container whilst still hot.
This procedure worked, but was very harsh on my glass jug, which ultimately cracked (I should have allowed it to cool more slowly by leaving it on the
hotplate).
RIP PYREX jug
Note the jug looks clean due to the strongly deliquescent nature of the calcium chloride.
[Edited on 13-8-2024 by Precipitates] |
This is precisely the method that I use!
The general procedure is:
1) Heat strongly until the calcium chloride "melts" into solution in the water of crystallization. Keep heating until you get a fused mass.
2) grind the fused mass into a powder, during which it will inevitably absorb some water.
3) strongly heat the powder to remove traces of water.
I use a coffee can with a lid, with the paint burned off, for the third stage.
You can heat it to red heat without melting the calcium chloride powder, then replace the cap when it is dry and still hot.
[Edited on 21-8-2024 by SplendidAcylation]
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Precipitates
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It works!
| Quote: Originally posted by SplendidAcylation |
I use a coffee can with a lid, with the paint burned off, for the third stage.
You can heat it to red heat without melting the calcium chloride powder, then replace the cap when it is dry and still hot.
[Edited on 21-8-2024 by SplendidAcylation] |
Yeah a can is a much better idea, and works as a neat storage container as well.
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