Question

A hydrate of CoCl2 has a mass of 15.80 g before heating. After heating, the mass of the anhydrous compound is found to be 9.32 g.

Explain how you would determine the formula of the hydrate and then write out the full name of the hydrate.

Answer 1

Let's suppose the formula is 

CoCl2.nH2O

CoCl2.nH2O−> CoCl2 + nH2O

H2O has the mss= 15.8-9.32 = 6.48g
 H2O contains moles= 6.48/(1.0x2+16.0) = 0.36
Moles in CoCl2 = 9.32/(58.9+35.5x2) = 0.071747
n = 0.36/0.071747
= 5