Which is the excess reactant in the following reaction given that you start with 15.5 g of Na2S and 12.1 g CuSO4?
Reaction: Na2S + CuSO4 ? Na2SO4 + CuS
A) Na2S
B) CuSO4
C) Na2SO4
D) CuS
E) not enough information
Answer: A