Calcium Chloride

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I guess to sum up, If the dihydrate's going cheap, then go for it. Me being the way I am, I'd go for the kilo of lab grade ;)
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A little bit of chemistry formula fun for anyone who may be interested:
number of moles (unit = mole) = mass (unit = grams) / relative molecular mass (unit = grams per mole)
or n = m / Mr

A mole (aside from being a little furry critter) is a unit for the "amount of stuff", so by knowing the relative molecular mass of one form, lets us work out how much of another (in grams) we'd need.

Relative molecular masses can usually be obtained by wiki or a database, but can be got by just adding up how many atoms of a certain type are in the molecule you're looking at, then multiplying by the relative atomic mass (which can be obtained from the good ol' periodic table) and summing up the values.
e.g. for CaCl2.2H2O, Mr = 40 + (2 x 35.5) + (4 x 1) + (2 x 16) = 147 g/mol (atomic mass of calcium is ~40 and that of chlorine is ~35.5, Hydrogen ~1 and oxygen ~16)

Doing this:
Mr of anhydrous = 111 g/mol
Mr of dihydrate = 147 g/mol
Mr of hexahydrate = 219 g/mol

If we say that we have 1 gram of the dihydrate, then we can work out that we have (1g) / (147g/mol) = 0.0068 moles of calcium chloride dihydrate present (that's around four thousand one hundred billion billion molecules :grin:). Rearranging the formula to get mass, and plugging in the relative molecular mass for the hexahydrate, we get 0.0068 mol * 219 g/mol = 1.489 grams (so 1.5 g). This means that for every gram of dihydrate that is needed, you can throw in 1.5g of hexahydrate instead and it'll contain the same amount of calcium ions (and chloride).
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tl;dr version: It's all calcium chloride, just with more or less water associated. If you're more comfortable sticking with the dihydrate, then you're probably very sensible. If you like a bit of maths and want to do some calculations, here's how :D. That's made me thirsty, time for a pint.
 
Aleman said:
calcium chloride is deliquescent. it will continue to absorb water, until it becomes a concentrated solution of calcium chloride. This is how those 'water traps' work. . . . Keep it sealed away from moisture when not in use. . . . I have it in a seal container inside a vacuum sealed bag
One way out of that is to make it up into a standard solution as soon as you get the stuff. I'll leave you to do your own sums, but 1 kilogramme could probably be made-up to two litres without exceeding saturation. Then 100ml is equivalent to 50 grammes of the stuff. In practice you choose the ratios such that you get nice round numbers of something useful, like calcium or milliequivalents, per 100ml, with the type of calcium chloride that you have. Its how breweries use it.
 
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