Calculate the mass of zinc required to produce 4 moles of zinc sulfide.

Given:
m (ZnS) = 4 mol
To find:
m (Zn) =?
Decision:
1) Let’s compose the equation of a chemical reaction.
Zn + H2S = ZnS + H2
2) Find the mass of zinc sulfide.
n = m / M, hence m = n x M
M (ZnS) = 65 + 32 = 97 g / mol
m (ZnS) = 4 x 97 = 388 g / mol.
3) Let zinc be x g, then:
x: 65 g / mol = 388 g: 97 g / mol
x = (65 x 388): 97 = 260 g.
Answer: m (Zn) = 260 g.