1.

FeO crystal has a simplecubic structureand each edge of the unitcell is 5 Å . Takingdensity of the oxide as 4g/cc, the number ofFe^(2+) and O^(2-)ionspresentin eachunitcell are

Answer»

`4 Fe^(2+) and 4O^(2-)`
`6FE^(2+) and 6O^(2-)`
`2Fe^(2+) and 2O^(2-)`
`1Fe^(2+) and 1O^(2-)`

Solution :Volume of unit cell = `( 5xx 10^(-8))^(3) cc`
` 1.25xx 10^(22) cc `
Density of FeO = 4 g/cc
Mass of unit cell = ` 1.25 xx 10^(-22) xx 4 = 5 xx 10^(-22) g `
Mass of 1 molecule`= 72/ ( 6.023 xx 10^(23)) = 1.195 xx 10^(22) g `
HENCE,number of FeOmolecules PER UNITCELL
` (5 xx 10^(-22))/( 1.195 xx 10^(-22)) = 4.18 =4 `
Hence, there are four `Fe^(2+)`and four ` O^(2-)`ions in eachunitcell,.


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