Pyrite (FeS2), crystallizes in a cubic unit cell with a cell edge of 0.540nm. The density of pyrite is 5.02g/cm3. How many Fe2+ and S2−2 ions are present in a single unit cell? (S=32u,Fe=56u)
A
1Fe2+and1S2−2
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B
2Fe2+and2S2−2
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C
4Fe2+and4S2−2
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D
6Fe2+and6S2−2
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Solution
The correct option is C4Fe2+and4S2−2 We know that, d=ZMa3NA
d - density of the crystal,
Z- Number of unit cell
MM - Molecular mass
a - edge length NA - Avagadro number
5.02=n(120)6.023×1023(5.4×10−8)3 ⇒n=4, i.e., 4Fe2+ and 4S2−2