Calculate the mass fraction of each element copper (2) -CuS sulfide.

Formula for calculating the mass fraction of an element in a substance:
w = n * Ar (chemical element) / Mr (substance), where n is the number of atoms of a given chemical element.

1) Find the relative molecular weight of the substance (CuS):
Mr (CuS) = Ar (Cu) + Ar (S) = 64 + 32 = 96;
2) Find the mass fraction of a given element in the substance:

w (Cu) = 64/96 = 0.67 or 67%
1 way: w (S) = 32/96 = 0.33 or 33% or 2 way: w (S) = 100 – 67 = 0.33 or 33%
Answer: Mass fraction of copper in copper sulfide (2) is 67%. Mass fraction of sulfur in copper (2) sulfide is 33%.