Sciencemadness Discussion Board

How can I boil off water from a calcium chloride solution

A Halogenated Substance - 22-3-2017 at 09:32

What's was the size of your container? By using a larger container, using stirring, and maybe blowing a fan over the solution, you could minimize 'overflowing'.

Were you also keeping track of the temperature? If you use too high a temperature, the boiling may get too vigorous.

Potentially, there could also be excess HCl boiling out of solution...
Did you use a stoichiometric amount of HCl solution or an excess?

Details would help.

ferrousexplosive - 12-7-2017 at 18:14

It is quite dificult since its a delisquesent substance, it absrobes humidity from air to form a solution, depending in the use you have for it there are some ways, if you are going to use it ti dry another compound like i almost always do, i recomend you to put it in a oven at low temperature (obviously enough to evaporate water) for like an hour and a half, or when you see its dry, then check if its enogh dry. Depending in the purity you may hope to use it in synthesis you could use another salt or substance even MORE delisquesent than CaCl2 to dry it completely.

I usually store it in a tight cap jar or bottle, right after getting it out from the oven. The first time i let it like for 5 minutes before putting it in the jar, and it was a LIQUID again, for the temperature it had though.

I hope this helps you, sorry for my english.

NEMO-Chemistry - 13-7-2017 at 17:49

I tried this with a microwave, to be really honest i started with calcium carbonate and HCL. I did it fairly large scale and what I got at the end of alot of work was not really worth it.

I like making reagents but I got to say I honestly think this is one best purchased, others may have had alot more luck that me but it was a complete mare to get dry.

Chemetix - 14-7-2017 at 20:50

I had some on a hotplate drying as this post came up; as it turns out hitting it with a bit of microwave energy to get it to speed up the process works. Then just keep giving the syrupy mixture a bit of a stir as the bottom drys up while on a hotplate. After a while the mix reaches a point where it has some lumps that stay slightly hydrated.

At this point I put it in the freezer, the freezer elements are cold enough to reduce the vapour pressure lower than the CaCl2. Dried it fine!

JJay - 14-7-2017 at 21:06

CaCl2 can form a hexahydrate at low temperatures, crystallizing while still containing large amounts of water. The crystals will melt very easily if heated. If you heat it on low heat in an oven, it will slowly dry out, allowing you to crank up the heat. I haven't tried it with calcium chloride in particular, but for many salts if you drive off the water too fast it will bump and make a big mess in your oven. I have little doubt that calcium chloride does the same.

NEMO-Chemistry - 15-7-2017 at 04:44

There you go i learnt something useful!!! i made mine from sea shells, just as a general purpose desiccant for the desiccator. I didnt have access to a normal oven, but i have just won a ultra cheap used kitchen on ebay :D. i want the cupboards etc for my lab, but it also comes with a crap oven,fridge and AND DISHWASHER!! Deep joy and happiness.

£35 all in but I have to go collect it. I have a microwave but the addition of a small oven would be really handy.

fluorescence - 15-7-2017 at 11:42

I'm not sure if you can really dry CaCl2 that easily. Many chlorides like LiCl cannot be dried that easily. There are methods like the HCl method where dry HCl or Sulphur Chlorides are used to dry it. But thermally drying it will often produce side produts like Oxychlorides etc. The reason for this is quite easy to explain. I even uploaded that on the pictures thread some time ago. In CaCl2 x 6 H2O you have the calcium surrounded by a trigonal prism of H2O where each square surface is capped by another H2O. So you end up with 9 water arround Calcium. This stacks along one axis and therefore three H2O are shared and you end up with the composition of a hexahydrate (in case you ever wondered why Ca forms hexahydrates). Now the Calcium is surrounded by water and the posive hydrogen on the other end hold the chloride. Therefore Ca and Chloride never meet, they don't even see each other. In solution the Ca is automatically coordinated by water and once you crystallize it this structure I explained above forms.

If you remember Be and Al compounds they tend to have a short and strong M-O bond, so short that the H(+) is eaily given off, which is why they can be turned to something like Beryllates or Aluminates quite easily. I guess something similar happens here. Once you apply more force the system will react in a stronger Ca-O bond than kicking off 6-9 water ligands which gives you CaOCl systems....

There are methods to make anyhdrous Chlorides (I remember this was like 3 lectures in Advanced inorganic chemistry, how to make anhydrous chlorides. This shows you that Chlorides are really special and they are not formed that easily in an anhydrous manner like you would expect it.

JJay - 15-7-2017 at 12:00

Calcium chloride is much easier to dry than, for example, aluminum chloride or zinc chloride. It's not as easy to dry as, for example, sodium chloride, but it can be dried to nearly anhydrous condition with heat alone (note that the process outlined here is not practical in a home lab, however):

Chemetix - 15-7-2017 at 14:59

The patent gives quite a good overview of the problem; from a practical standpoint too. It was quite obvious from the patent that leaving it in a beaker to dry was never going to work. The bottom layer dries and the top just takes up more moisture from the crystalline layer below it. Some agitation is required to mix the progressively lower hydrated forms and increase the surface area.

Once the limit of dehydration is reached by heating it, the freezer is able to take that little bit more water. I don't assume it would be anhydrous, but good enough for a simple desiccant. The microwave only works, as others have pointed out, up until it starts to spatter badly.

I was only bothering to dry some out because I was wondering how to reuse the hydrated salt in a process. How much water can it absorb after it has been "dried"?

JJay - 15-7-2017 at 15:20

Don't bother putting it in the freezer unless you actually want hexahydrate crystals for some reason (I've done this; it's actually a bit tricky because they dissolve very easily in very cold water, and if you undershoot the mark you will obtain only a solid amorphous mass of calcium chloride in mixed hydration states). The limit of dehydration that can be reached by heating it is the anhydrous form, but it is going to take a very long time to approach anhydrous in a regular oven.

Chemetix - 15-7-2017 at 17:06

Has anyone tried heating under reduced pressure?

Just gave the crystals from the freezer a microwave treatment.
2-5 second reaction no perception of heating in the crystals
8-10 seconds. Big puff of steam and fluffy mass, easily broken down with a metal utensil. Some hard mass lining the walls which flake off with some effort.

JJay - 15-7-2017 at 17:36

That's a very interesting idea.