An 11.75 g sample of a common hydrate of cobalt(ii) chloride is heated. after heating, 9.25 g of anhydrous cobalt chloride remains. what is the formula and name for this hydrate?

Hydrated salts are when salt crystals have water molecules bound. Anhydrous salts are when the water has been removed.
mass of water removed = hydrated salt - anhydrate salt 
                                       = 11.75 g - 9.25 g = 2.50 g
number of water moles  = 2.50 g / 18 g/mol = 0.139 mol 
number of cobalt (II) chloride moles = 9.25 g / 130 g/mol = 0.0712 mol 
ratio of water moles to CoCl₂ moles - 0.139 mol / 0.0712 mol = 1.95 
rounded off 2 moles of water for every 1 mol of CoCl₂
formula - CoCl₂.2H₂O
name - Cobalt(II) chloride dihydrate

The answer is celsius