When burning 96 kg of pyrite (a mineral containing FeS2), sulfur dioxide with a volume of 30.69 m3 was formed.

When burning 96 kg of pyrite (a mineral containing FeS2), sulfur dioxide with a volume of 30.69 m3 was formed. Calculate the mass fraction of non-combustible impurities in pyrite.

1) Let’s compose the equation of combustion of pyrite:
4FeS2 + 11O2 = 2Fe2O3 + 8SO2 ↑
2) Calculate the amount of sulfur dioxide substance:
n (SO2) = V (SO2) / Vm = 30.69 / 22.4 = 1.37 kmol.
3) Determine the mass of pure FeS2, the mass of impurities and their mass fraction in the original substance:
Let the amount of pyrite matter per 1.37 kmol of sulfur dioxide is x.
Then, according to the reaction equation, we compose the proportion:
x / 4 = 1.37 / 8
n (FeS2) = 0.685 kmol.
The mass of pure pyrite reacted is:
m (FeS2) = n (FeS2) ∙ M (FeS2) = 0.685 ∙ 120 = 82.2 kg.
the mass of impurities is:
m (impurities) = 99 – 82.2 = 13.8 kg
Mass fraction of impurities:
ω (impurities) = (m (impurities) ∙ 100) / m (pyrite) = 13.8 ∙ 100/96 = 14.375%