Let the number of moles of water in the required formula be "y".
The final formula should be in the form of : CoCl2 yH2O
1.62 g is the weight of CoCl2 and water in the sample
After heating, the remaining mass represents the mass the salt only
mass of water in sample = 1.62 - 0.88 = 0.74 g
From the periodic table:
molar mass of cobalt is 59 g
molar mass of chlorine is 35.5
molar mass of hydrogen is 1
molar mass of oxygen is 16
molar mass of formula = 59 + 2(35.5) + 18y = 130 + 18y g
Now we have calculate the mass/molar mass for each part of the formula (salt and water) and equate them to get number of moles of water as follows:
0.88 / 130 = 0.74 / y18
y = 6.07 which is approximately 6 moles
Thus, the final formula is CoCl2 6H2O. This hydrate is called cobalt(II)chloride hexahydrate.
