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

Explanation:

Molar mass of Cobalt (II) chloride = 129.8g/mol

Moles of CoCl2 = 9.32/129.8 = 0.0718mol

Mass of H2O lost after heating = 15.80 - 9.32 = 6.48g

Moles of H2O = 6.48/18 = 0.36mol

Mole ratio of CoCl2 : H20

= 0.0718mol : 0.36mol

= 1 : 5

Hence the formula is CoCl2 . 5H2O, which is Copper (II) chloride pentahydrate.