Preparation of anhydrous CoCl2
Cobalt(II) chloride hexahydrate is a chemical which can be purchased fairly easily. It sometimes is offered on eBay: http://stores.ebay.co.uk/Metals-Chemicals.
The anhydrous form can easily be prepared from the hydrated form by careful heating. Most important is that the heating is done really carefully. Too fast and too strong heating results in loss of hydrogen chloride, and then the oxide or an insoluble oxychloride is obtained. With careful heating, however, one can obtain a nice anhydrous salt, which dissolves in water clearly.
The procedure for making the anhydrous salt is simple. Start with the hydrated salt. Put some in a beaker or erlenmeyer.
The hydrated salt, which is purple/red, then carefully is heated. Initially, the salt seems to melt, and its color shifts from purple/red to dark blue.
In reality, this is no real melting, but the salt dissolves in its own water of crystallization. The blue color is due to formation of a four-coordinated complex, instead of the six-coordinated hexaaqua complex of cobalt(II).
When the liquid is heated carefully, then the water can be boiled off slowly. When most of the water is evaporated, then the color of the liquid shifts from dark blue to a lighter blue, with a dull cyan hue. Once, the material seems reasonably dry, then one can heat the solid more strongly to drive off the last remains of water. As long as water is present, however, the heating must be done carefully, otherwise HCl is driven off instead of water, and an oxide or oxychloride remains instead of the anhydrous chloride.
The final product of careful heating is a blue powder:
When this powder is added to water, then it dissolves, giving a pink and clear solution. When this powder is allowed to stand in contact with air, then it first turns somewhat green, but on longer standing, especially in contact with humid air, it quickly becomes purple/red again.