what is the difference between hexahydrate and dihydrate?

[john6]

Apart from the obvious 6 and 2 what is the difference?
Ive buying some calcium chloride and the one ive seen cheaply is the Hexahydrate, so is it ok to use that rather than Dihydrate? and would the measurements still be the same as Dihydrate?

 

[_Maq_]

is it ok to use that rather than Dihydrate? and would the measurements still be the same as Dihydrate?

It is ok to use both, but the measurement will NOT be the same.
This salt forms crystals with water. Either one molecule of CaCl2 with two molecules of water, or with six molecules of water. The latter contains more water, so you'll have to dose more of it.

 

[john6]

It is ok to use both, but the measurement will NOT be the same.
This salt forms crystals with water. Either one molecule of CaCl2 with two molecules of water, or with six molecules of water. The latter contains more water, so you'll have to dose more of it.

Thanks
I'll look for the Dihydrate then

 

[dw1305]

Hi all,

Ive buying some calcium chloride and the one ive seen cheaply is the Hexahydrate

It is incredibly hygroscopic (you can use it <"as a desiccant">) so in practice it is is always the hexahydrate (CaCl2.6H2O) when you use it, even if you bought it as the dihydrate (CaCl2.2H2O), if that makes sense?

You've still got one calcium and two chlorines, so the only difference is, like @_Maq_ , says you have to take into account the extra wt. of the four extra molecules of the "water of crystallization" (18 x 4 = 72). This means it is simple conversion to go from one to the other.

and would the measurements still be the same as Dihydrate?

Just add a third in weight for the hexahydrate.

The calcium content of the hexahydrate (CaCl2.6H2O) is 18.3% (RMM = 219 (147 + 72)) and of the dihydrate (CaCl2.2H2O) 27% (RMM = 147), which means that:

If you needed to add 10g of CaCl2.2H20 to get to your calcium target, you need to add 15g of CaCl2.6H20.

cheers Darrel