Calculate the mass of a contaminated 20% zinc sulfide sample required to produce 25.6 g sulfur dioxide

Given:
ω (ZnS) = 20%
m (SO2) = 25.6 g

Find:
m tech. (ZnS) -?

1) 2ZnS + 3O2 => 2ZnO + 2SO2;
2) n (SO2) = m / M = 25.6 / 64 = 0.4 mol;
3) n clean. (ZnS) = n (SO2) = 0.4 mol;
4) m clean. (ZnS) = n pure. * M = 0.4 * 97 = 38.8 g;
5) m tech. (ZnS) = m pure. * 100% / ω = 38.8 * 100% / 20% = 194 g.

Answer: The mass of technical ZnS is 194 g.