The initial sample has a molecular formula of MnSO₄·H₂O. This molecule is a hydrate as it has a unit of water within its structure for every molecule of MnSO₄. This sample is being dehydrated to remove the water to give.
MnSO₄·H₂O → MnSO₄ + H₂O
MnSO₄·H₂O has a molecular mass of 169.02 g/mol. While MnSO₄ has a molecular mass of 151 g/mol. Water has a molecular mass of 18.02 g/mol. We now can use the ratio of the mass of water to the mass of the initial sample to determine the percentage of each component by mass.
% water by mass:
18.02/169.02 x 100% = 10.7% Water by mass.
% MnO₄ by mass:
151/169.02 x 100% = 89.3% MnSO₄ by mass.
Water makes up 10.7% of the initial mass of MnSO₄·H₂O.
