How much Calcium Chloride is this?
- Thread starter Buna_Bere
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That would be 1 gram CaCl2 = 72 ppm Ca per gallon.
In fairness to you, the folks at the Emporium could have come up with a more informative label...
Cheers!
Well the label says it is CaCl2. If you put 1 gram of that in 1 gal of water you will get 95.4 ppm Ca++ and 168.9 mg/L Cl-. If, OTOH, you put 1 gram of the dihydrate (CaCl2.2H2O) in 1 gal of water you would get the numbers on the label. So either the CaCl2 labeling is wrong or the concentrations are wrong.
BrewKnurd
Well-Known Member
haha, i just noticed that they didn't even get the formula of CaCl2 right... they call it calcium chloride, but then list it as CaCl.
I didn't notice the missing 2!
Well you got me curious which kind it was, so I asked. Here's my email and the response.
Hi, I purchased a small container of Calcium Chloride from the Cambridge shop a couple of weeks ago, and I had a question about what kind of Calcium Chloride it actually is. Is it CaCl2 or is it the dihydrate CaCl2.2H20?
Thanks,
Bob
"I have no idea, but we sell two varieties, a dry one and a liquid one.
I assume the dry type is anhydrous and the liquid is the dihydrate."
So now my new question is since this is the dry one, does this mean I'm getting 95.4ppm Ca per gram?
Afraid it isn't that simple. Calcium chloride, CaCl2.nH2O exists for n = 0,1,2,4, or 6 (those are all the one's I've heard of anyway). I have never been able to determine, short of assay and my assays haven't left me with warm tummy feelings, what n might be for stuff I buy from the LHBS. If I buy it from a chemical supply house and it says dihydrate on the label and its ACS grade then I'm confident that I'm getting CaCl2.2H2O. Otherwise I'm not. Most calcium chloride contains, for example, some calcium hydroxide and there is no reason, really, why n couldn't be a non integer number (implying that the product is a mix of more than one type). In my calculations I tend to use n=1 assuming that the actual is equally likely to be the anhydride or the dihydrate (for years I assumed it was the dihydrate until I started to look into it a little) and thus "splitting the difference".
AJ,
Calcium chloride is highly hygroscopic, so isn't it possible that the stuff is coming from a supplier and over time picking up water? Maybe that's why your findings are inconclusive. I guess we all need to be concerned with that. As I recall, the temperature needed to move these various hydrates back toward an anhydrous state increase with each hydrate reduction.
Do I recall correctly that the best we could probably do in drying out these hydrates in a typical home oven is about the dihydrate version?
Calcium chloride is highly hygroscopic, so isn't it possible that the stuff is coming from a supplier and over time picking up water? Maybe that's why your findings are inconclusive. I guess we all need to be concerned with that. As I recall, the temperature needed to move these various hydrates back toward an anhydrous state increase with each hydrate reduction.
Do I recall correctly that the best we could probably do in drying out these hydrates in a typical home oven is about the dihydrate version?
When we buy it it's sealed in those little handy jars but somewhere along the line someone bought it in bulk and put it in those little jars and during that process there is a good possibility that it picked up water. Then, of course, we open the jar, take out a little and close it again. More exposure to air. OTOH if you look at specs for CaCl2 you see things like 77-80% with Dow bragging that theirs is 80 - 83%. I think this probably represents a mix of anhydride and dihydrate (though there are other impurities to like the calcium hydroxide I mentioned in an earlier post).
Thanks for the compliment but it's probable that a lot of it is that I'm not familiar with the assay and am screwing it up.
I guess if you are really concerned about accuracy the thing to do is buy the liquid* or laboratory grade stuff that comes with the assay on the label. Probably for most of what we do it is sufficient to call it the monohydrate which would be about 87% or to assume it's 80% and add 25% to all weighings.
The melting points go up as the waters of hydration decrease. I think "melting" really means melting in the case of the anhydride which melts at 772 °C (according to Wilipedia) but in the case of the hydrated salts it really means that the water of hydration is released so that it looks as if it's melting but it is really swimming in its own water of hydration.
Again according to Wikipedia (who needs the CRC Handbook any more?) the monohydrate "melts" at 500 °F. That's probably a reach for most home ovens. The dihydrate melts at 348 though and that's not.
One can heat small quantities of the powder with a Bunsen burner or propane torch however. I heated 5 grams of the stuff from the LHBS to about 900 °F as a consequence of which it lost 3.8% of its weight. The monohydrate is 14% water so that again suggests that the product is a mix. About 5 grams of the dihydrate heated to about 700 °F lost 33.5% of its weight. The dihydrate is about 24.5% water which suggests that this stuff, in a jar so old that the powder is caked, has picked up moisture over the years. Also of interest is that this mass picked up 38 mg of water in an hour from the low humidity air in the room.
* The liquid is pretty easy to make. Weigh out 100 grams of calcium carbonate (chalk) i.e. one mole. Add to it 100 mL of 12 M (approximate strength of "concentrated") hydrochloric acid or 200 mL of concentrated that has been diluted 1:1 (6 N). Add the acid slowly to minimize splatter from fizzing. Be sure that all the chalk is dissolved using extra acid if necessary. Now evaporate to dryness. Dissolve the powder in DI water, quantitatively transfer to a 1L volumetric flask and make up to the mark. This is 1 M CaCl2 i.e. each mL contains 110.98 mg of CaCl2.
