Answer:
It is cobalt (II) chloride dihydrate, CoCl2.2H2O.
X = 2
Step-by-step explanation:
We can calculate the value of x using the formula:
RMM of nH2O/RMM of anhydrous salt = mass of water expelled or absorbed/mass of anhydrous salt
Where RMM of nH2O= relative molecular mass of nH2O =n[ (1 X 2) + 16 ]= 18n where n = number of moles of water of crystallization = x
RMM of anhydrous salt= RMM of CoCl2= 58.9+(35.5 X 2) = 129.9
Since the mass of the hydrated salt decreased by 22%, and assuming we have 100g of original sample,
Mass of water expelled = 22g
And (100-22)g of anhydrous salt will remain after heating off all the water, so,
Mass of anhydrous salt = 78g
Substituting the values into the formula,
18n/129.9 = 22/78
18n X 78 = 129.9 X 22
1404n = 2857.8
n = 2857.8/1404
n = 2.035470085
n = 2 ( to the nearest whole number )
You can check if your answer is correct by using this formula to calculate the percentage of water of crystallization in CoCl2.2H2O:
% of water of crystallization = (mass of water expelled/mass of hydrated salt) X 100
Where mass of water expelled = mass of 2H2O = 2.035470085 X 18 = 36.63846154
Mass of hydrated salt = mass of CoCl2.2H2O = 129.9 + 36.63846154 = 166.5384615.
Substituting into the formula we have
% of water of crystallization = ( 36.63846154/166.5384615) X 100.
% of water of crystallization = 0.22 X 100 = 22%.
Notice that we used the actual value of the number of moles of water of crystallization in calculating the percentage to minimize errors and avoid approximate percentage composition values. But we used 2 for the formula of the hydrated salt because we had to round off the value to the nearest whole number