how to I figure how much copper is in 2.154 gram of copper sulfide?

2 answers

gramsCu= 2.154*percentcompositionCu in CuS

= 2.154* (atomicwtCu/(atomicWtCu+atomicWtS)
Copper sulfide is CuS.
The ratio of the atomic weights of Copper and Sulfur is the ratio of the masses of those two elements.

That ratio is 63.5/32.0.

63.5/(63.5+32.0) = 63.5/95.5
= 66.5% of the mass is copper.