Describe briefly how pure dry crystals of calcium chloride can be obtained from its solution
2 answers
boil the water off ?
To add to what Damon has answered.
Boiling the water off probably will produce a hydrated form of CaCl2; i.e., either CaCl2.2H2O, CaCl2.4H2O, or CaCl2.6H2O. In order to drive off the water of hydration you much use higher temperatures. I have been unable to obtain thermograph data giving the exact temperature for EACH of the hydrates but you can drive off ALL of the water by heating the resulting material from the boiling off stage up to 772 C (or slightly higher). This melts the anhydrous CaCl2. Then cooling it produces solid anhydrous CaCl2. Unfortunately, that isn't the end of the problem. Anhydrous CaCl2 is EXTREMELY hygroscopic. In fact it is delinquent meaning that it immediately starts picking up moisture from the atmosphere. It is so efficient that it picks up enough moisture to, as I put it, dissolve in its own soup. So you can get CaCl2 with no hydration this way but you can't keep it that way very long. . It could be stored under a vacuum. Hope this helps.
Boiling the water off probably will produce a hydrated form of CaCl2; i.e., either CaCl2.2H2O, CaCl2.4H2O, or CaCl2.6H2O. In order to drive off the water of hydration you much use higher temperatures. I have been unable to obtain thermograph data giving the exact temperature for EACH of the hydrates but you can drive off ALL of the water by heating the resulting material from the boiling off stage up to 772 C (or slightly higher). This melts the anhydrous CaCl2. Then cooling it produces solid anhydrous CaCl2. Unfortunately, that isn't the end of the problem. Anhydrous CaCl2 is EXTREMELY hygroscopic. In fact it is delinquent meaning that it immediately starts picking up moisture from the atmosphere. It is so efficient that it picks up enough moisture to, as I put it, dissolve in its own soup. So you can get CaCl2 with no hydration this way but you can't keep it that way very long. . It could be stored under a vacuum. Hope this helps.