I\'m studying for the FE and don\'t really know how to do this problem. Please s
ID: 883450 • Letter: I
Question
I'm studying for the FE and don't really know how to do this problem. Please show work, so I can follow and learn how to set up and execute these problems.
Impure iron pyrite (FeS2 and inert) is burned in a sulfuric acid plant to produce a feed gas with the following Orsat analysis.
SO2 = 8.5% O2 = 7.0% N2 = 84.5%
Note that SO3 is also present but cannot be estimated with an Orsat analysis.
The impure pyrite contains 46 wt% sulfur. The solid refuse from the burner, cinder, contains 3 wt% sulfur as Fe2(SO4)3. The expected reactions include
4FeS2 + 15 O2 = 2Fe2O3 + 8 SO3
4FeS2 + 11 O2 = 2Fe2O3 + 8 SO2
Fe2O3 + 8 SO3 = Fe2(SO4)3
Molar masses that pertain to this process include
FeS2 120.0
Fe2O3 159.7
Fe2(SO4)3 400.0
O2 32.0
N2 28.0
SO2 64.1
SO3 80.1
Fe 55.85
S 32.1
The amount of inert material (wt%) in the crude pyrites is most nearly
A. 8
B. 14
C. 31
D. 54
Explanation / Answer
Let there be 100 gram of impure pyrite.
S in it is 46% that is 46 gm
Number of moles of sulphur= mass/molar mass = 46/32 = 1.4375 mol
Number of moles of Fe = mass/molar mass =1.4375/2 = 0.71875 mol
Mass of fe = Molar mass * number of moles = 56* 0.71875 = 40.25 gm
Impurities mass = 100 - 46 - 40.25 = 13.75
So impurities are roughly 14 %
Answer: B.14