The percent by mass of Tin : = 27.08%
Given
25.00 g of the compound
6.77 g of Tin
18.23 g of Bromine
Required
The percent by mass of Tin
Solution
Proust stated the Comparative Law that compounds are formed from elements with the same Mass Comparison, so that compounds have a fixed composition of elements
%mass X = (mass X/mass sample) x 100%
So %mass of Tin :
= (6.77 g : 25 g) x 100%
= 27.08%