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a crystalline compound on heating looses 51.2% by mass to form the anhydrous compound.The anhydrous compound contains Mg-20%,S-26.66%,O-53.33%.The molecular mass of the anhydrous compound is 120,find out the formula of the crystalline compound.(best of luck)
In anhydrous salt, the percentage of all the elements is as follows

Mg = 20.0%

S = 26.66 %

O = 53.33 %

Therefore 100 g of the anhydrous compound will have 20 g of Mg, 26.66 g of S and 53.33 g of oxygen.

Therefore number of moles in 20.0 g of Mg = 20 / 24 = 0.833

number of moles in 26.66 g of S = 26.66 / 32 = 0.833

number of moles in 53.33 g of O = 53.33 / 16 = 3.333

To obtain the simplest ratio, we will divide number of moles of all the elements by the smallest number that is 0.833. Hence division of number of moles of all the elements by 0.833 gives a ration of 1:1:4 for Mg:S:O.

So the empirical formula is MgSO4. The empirical formula mass is [24 + 32 + (4 X 16)] = 120.

As the molecular mass of the anhydrous salt is 120g, therefore the molecular formula is the same as the empirical formula is MgSO4.



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