Sciencemadness Discussion Board

Gah, I ruined my calcium chloride, how did it happen?

jsc - 1-2-2015 at 19:26

I bought some Morton de-icer which is advertised as being "pure" calcium chloride.

It comes in the form of small white pellets.

Thinking to dessicate it, I put 1500 grams of the stuff in a microwave and left it on high for 15 minutes. It weighed 1490 grams after that process.

When I took it out, big clumbs had formed and turned brownish yellow, so I am thinking is that chlorine dissolved into it? Did it decompose?

I assumed that the decomposition temperature would be way over what the microwave could do. I know the melting temperature is 775 C.

So what happened? My main theories:

(1) I just melted it and melted CaCl2 happens to brownish yellow?

(2) I decomposed it and the yellowish-brown is because of free chlorine.

(3) There was a lot of water stored in it, and when I heated it the water came out and then somehow made the CaCl2 into mush, which happens to be yellow for some unknown reason.

Help me out, what happened?



[Edited on 2-2-2015 by jsc]

Volanschemia - 1-2-2015 at 19:34

I bought CaCl2 as a desiccant and when I dissolve it in water I end up with a fair amount of insoluble yellowish particles floating in the water. My source was advertised as 99%. It's possible that water has come out but wouldn't that just rehydrate it? Could you post a photo of it so we can see what it looks like?

Molecular Manipulations - 1-2-2015 at 19:37

Not entirely sure...
You didn't decompose it, that won't ever happen. My guess is it had iron chloride hydrate contamination. That will account for the loss of mass (water present would do the same) and the yellow-brown color.
You didn't ruin your calcium chloride. The iron was already present, you merely decomposed it from a compound with a faint color to iron (III) oxide.
You could probably dissolve in water, filter off the iron oxide, boil off the water, and re-microwave it if purity is desired.

jsc - 1-2-2015 at 19:50

I dissolved it in water and the water is definitely yellowish.

I have dissolved calcium choride in water before and it was never yellow, always perfectly clear. Could there be a contaminant?

jsc - 1-2-2015 at 19:52

Quote: Originally posted by Molecular Manipulations  
Not entirely sure...
You didn't decompose it, that won't ever happen. My guess is it had iron chloride hydrate contamination. That will account for the loss of mass (water present would do the same) and the yellow-brown color.
You didn't ruin your calcium chloride. The iron was already present, you merely decomposed it from a compound with a faint color to iron (III) oxide.
You could probably dissolve in water, filter off the iron oxide, boil off the water, and re-microwave it if purity is desired.


Interesting, why would it have iron contamination? How can I verify?

Volanschemia - 1-2-2015 at 20:00

Quote: Originally posted by jsc  
I dissolved it in water and the water is definitely yellowish.

I have dissolved calcium choride in water before and it was never yellow, always perfectly clear. Could there be a contaminant?


Is there any insoluble matter left when you dissolve it? If there isn't, then MM's theory on Iron contamination is likely. If it is an insoluble yellow compound then it's likely mixed impurities and you can clean via filtering.

If you want to check for iron(III) contamination, just add some Potassium Hexacyanidoferrate(II) to a small sample. If the solution turns blue, then there is Iron(III) present.

jsc - 1-2-2015 at 23:01

More information:

I dissolved about 100 grams of CaCl2 from the same batch in water and it looks a little syrupy, but clear, no yellow.

This is extremely mysterious. Why would the same CaCl2 dissolve clear into water, but after you microwave it, it turns yellow? Have I discovered the philosopher's stone?

Zombie - 1-2-2015 at 23:30

I was reading thru the dow handbook (pdf) http://www.prog-univers.com/IMG/pdf/CalciumChloridHandbook-2...

There is a section in it pertaining to temperature increase in heated Calcium Chloride.
Basicly it states that heated water will increase the temp. of the product exponentially.
Quoting:
"Thus, if
the temperature of the water is 23°C
(74°F), the final solution temperature will exceed 68°C (155°F) for
DOWFLAKE and 114°C (238°F)
for Anhydrous. "

Is it possible the the thermal reaction created by the moisture you were trying to remove on the "high" setting pushed your product to the decomposition stage?
I'll leave that calculation to you smart folks.

Quick edit.
Perhaps some given impurity is responsible? Perhaps that impurity was heated to decomposition? The point is the temperature was much higher in the sample than you believed.

[Edited on 2-2-2015 by Zombie]

macckone - 2-2-2015 at 01:01

Calcium chloride isn't going to decompose in a microwave.
Commercial grade deicer has a water soluble non hygroscopic
Coating that will decompose in heat. Don't ask what it is.
I don't know either but it is probably a sugar as it is environmentally
Safe and not listed on the msds.

woelen - 2-2-2015 at 01:34

The CaCl2 from hardware stores is quite impure. It is anhydrous, but it has a lot of organic impurities. On heating, that organic material chars and gives a yellow, or even a brown color to the solid.

Hardware store CaCl2 is fine for drying or deicing purposes, but if you want to do experiments with it, then you'd better search for another more pure source of calcium ions (e.g. you can buy very pure CaCO3 and dissolve that in acid, you can buy foodgrade CaCl2).

jsc - 2-2-2015 at 04:13

Quote: Originally posted by macckone  
Calcium chloride isn't going to decompose in a microwave.
Commercial grade deicer has a water soluble non hygroscopic
Coating that will decompose in heat. Don't ask what it is.
I don't know either but it is probably a sugar as it is environmentally
Safe and not listed on the msds.


I think this is right.

I noticed that in the water there were one or two tiny specks of black. Obviously we got organics in there that got charred by the heat.

AJKOER - 2-2-2015 at 07:44

I use DampRid as my source of pure CaCl2 that is designed and ready to absorb water (professly to remove moisture from your basement).

Unfortunately with time and exposure of the contents to air, it turns into [Edit] CaCl2.CaO.2H2O, for example (see
http://calcium.atomistry.com/calcium_oxychloride.html ).

It is also more expensive than de-icer, but I find the latter to be generally worthless for my needs.

[Edited on 2-2-2015 by AJKOER]

Praxichys - 2-2-2015 at 07:57

You could probably heat the calcium chloride in a metal can on a fire to char any organic stuff, then dissolve and filter the residue to catch the tars/carbon.

Add a small amount of hydrogen peroxide and boil the solution down to just before the saturation point. Filter it hot before cooling in the refrigerator to precipitate CaCl2·6H2O. Filter the crystals and wash with a minimum of near-freezing water. Microwave the filtered crystals to produce anhydrous CaCl2. The product should be substantially free of iron and any organic impurities.

woelen - 2-2-2015 at 07:58

AJKOER, please think twice before you post something. Sooo many of your posts simply are plain wrong!

Pure CaCl2 does not turn into CaCl2.CaO. It turns into CaCl2.xH2O and in the end it will liquefy if the air is really humid, giving a concentrated solution of CaCl2 in water.

If CaCl2 would turn into CaCl2.CaO, then where would the chloride go? It would leave as HCl and corrode everything nearby. Anhydrous CaCl2 is not stuff like anhydrous AlCl3 or NbCl5! If it were, then nobody would want to use it as drying agent for basements or other rooms.

CaO in turn is not stable in contact with air. It absorbs water and gives Ca(OH)2 and it may also absorb CO2, giving CaCO3.

Dan Vizine - 2-2-2015 at 08:12


Try stirring a sample of an aqueous soln. with a few wt. % activated charcoal for 15 minutes, then filter. Should give a much lighter to even colorless filtrate.

Don't use the crappy big balls of carbon you find in water filters, you want high surface area powder. If you can only get crappy big balls, pulverize first and use 2 or 3 times more.

Filter through several layers of filter paper, with the bottom layer as fine as is practical.

For more on the magic of activated carbon, try:
http://en.wikipedia.org/wiki/Activated_carbon





[Edited on 2-2-2015 by Dan Vizine]

AJKOER - 2-2-2015 at 09:04

Quote: Originally posted by woelen  
AJKOER, please think twice before you post something. Sooo many of your posts simply are plain wrong!

Pure CaCl2 does not turn into CaCl2.CaO. It turns into CaCl2.xH2O and in the end it will liquefy if the air is really humid, giving a concentrated solution of CaCl2 in water.

If CaCl2 would turn into CaCl2.CaO, then where would the chloride go? It would leave as HCl and corrode everything nearby. Anhydrous CaCl2 is not stuff like anhydrous AlCl3 or NbCl5! If it were, then nobody would want to use it as drying agent for basements or other rooms.

CaO in turn is not stable in contact with air. It absorbs water and gives Ca(OH)2 and it may also absorb CO2, giving CaCO3.


Sorry, I was going to add the link right away, but was pulled away, as this is not really my opinion.

Now, I have had my DampRid for nearly two years, and use it on occasion in the original package (which, in fairness, is not intended for long term storage). I am very very sure it is not the same product it was on first use. That product reacted noticably exothermically on contact with water. Today, it takes stirring just to get it to dissolve, but it does completely dissolve forrming a clear solution.

My opinion on the reaction with moist air to explain the claim of Calcium oxychloride formation:

2 CaCl2 + H2O --) CaCl2. CaO + 2 HCl (g)

That is, an excess of CaCl2 reacting exothermically with a small amount of water (moisture). Note, I would expect that the reaction of an excess of water on CaCl2 proceeds more likely per Woelen's assertion of CaCl2.xH2O (as any formed HCl vapors could be absorbed and reform the CaCl2 from the correspondingly created basic oxychloride salt).

At RT upon further exposure to moisture, the dihydrate appears to form:

CaCl2. CaO + 2 H2O = CaCl2.CaO.2H2O

Here is the precise quote from Atomistry link provided above and here again http://calcium.atomistry.com/calcium_oxychloride.html :

"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. .......Shreinemakers 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."

[Edited on 2-2-2015 by AJKOER]

Amos - 2-2-2015 at 09:14

Praxichys's method of purification sounds like the most worth your time to me. Just put the calcium chloride in an oven/furnace/etc. on a high heat setting to fully char whatever sort of coating is on it, and that should easily filter off once you've dissolved the calcium chloride back into solution. For some reason I get the feeling that a microwave wouldn't do this well as the air inside doesn't get very hot, but it might work all the same.

woelen - 2-2-2015 at 09:58

@AJKOER: You write about fusing the CaCl2.xH2O. Indeed, under such conditions some HCl may be lost and the material becomes alkaline. This effect is common with many hydrated salts. Many salts cannot be made anhydrous by simple heating, due to loss of acid and formation of basic salts. I know from experience with CaCl2 that the effect is not strong. CaCl2 can be dried by heating and only a very small amount of basic salt is formed. At room temperature, as is discussed in this thread, CaCl2 certainly does not lose HCl and no basic salts are formed under such conditions.

AJKOER - 2-2-2015 at 14:04

Sorry, I actually cited this before per my increasing declining recollection, to quote Atomistry.com on CaCl2 (see http://calcium.atomistry.com/calcium_chloride.html) and not from the oxychloride commentary:

"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."

Further, to quote from de Grupter's "Concise Encyclopedia Chemistry", page 162 on CaCl2:

"It is possible to completely dehydrate the hydrates by slow heating to 200 C. However, when the substance is heated too rapidly, it may partially eliminate HCl and form calcium oxide. These preparations give an alkaline reaction when dissolved in water."

From which my take is that rapid heating can produce uneven heating and pockets of dry CaCl2 subject to water vapor that can, per above, liberate HCl and form some CaO as well.

My speculation is that this same process may occur when anhydrous CaCl2 is exposed over time to water vapor given the heat of the CaCl2 hydration reaction, or some other pathway via the presence of impurities in my commerical grade calcium chloride, for example.

Being speculative, however, I will not longer assert it as a fact.

[Edited on 2-2-2015 by AJKOER]

MrHomeScientist - 5-2-2015 at 08:33

Why speculate when you can experiment? Test the pH of your old DampRid and let us know.

macckone - 5-2-2015 at 09:49

Hypothetically calcium chloride can oxidize to hypochlorite.
In reality this is going to be so slow as to be nonexistent
and the reverse reaction is much more favorable.

Hypothetically water can combine with the chloride to form
hydroxide and hydrogen chloride. In real life the thermodynamics
prevent this from happening to any significant extent.

Does it happen? Yes everything is an equilibrium.
To what extent? 1 ppm maybe, someone may be able to find a figure.

Dan Vizine - 6-2-2015 at 17:20

Or, you could just conclude that the answer isn't deserving of much time. You can buy fused, food-grade calcium chloride for less than $11 per 100 g delivery included on e-Bay.

jsc - 7-2-2015 at 20:06

Quote: Originally posted by Dan Vizine  
Or, you could just conclude that the answer isn't deserving of much time. You can buy fused, food-grade calcium chloride for less than $11 per 100 g delivery included on e-Bay.


LOL $11. De-icer costs 7 cents for 100 grams. See the cost difference there?

You are proposing a solution that costs 150 times as much.

macckone - 7-2-2015 at 21:36

Food grade items are made by purifying non-food grade materials.
We are here to talk about the chemistry of such things.
Of course making food grade calcium chloride involves first
treating with a small amount of sodium carbonate then a small
amount of sodium hydroxide to precipitate things that are more
easily converted from a chloride to a carbonate or hydroxide and
are less soluble that the corresponding calcium compounds.
Then a much larger quantity of sodium hydroxide is added to
precipitate the calcium hydroxide. The hydroxide is then rinsed
and finally the hydroxide is converted back to chloride with
hydrogen chloride gas. The liquid calcium chloride solution
is then boiled to cake, ground or flaked then if needed pelletized.