# What is the percentage of water in CoCl_2 * 6H_2O?

"%Water = " "Mass of water"/"Molar mass of cobaltous chloride hexahydrate"xx100%
So, (6xx18.01*g*mol^-1)/(237.93*g*mol^-1)xx100%~=50%
The hexahydrate has a beautiful purple colour. The anhydrous salt, $C o C {l}_{2}$, has an equally beautiful blue colour.