1.

A face centered cubic solid of an element ( atomic mass 60) has a cube edge of 4Å. Calculate its density.

Answer»

SOLUTION :Edge length`= 4 Å = 4 xx 10^(-8) cm`
VOLUME of unit cell = ` ( 4 xx 10^(-8) cm)^(3)`
`64 xx 10^(-24) cm^(3)`

Mass of the unitcell = Number of atoms in the unit cell ` xx ` mass of each atom
Number of atomsin the fcc unitcell
` 8 xx 1/8 + 6 xx 1/2= 4`
mass of oneatom =` (" AtomicMass")/( " Avogadro number") `
` = 60/( 6.023 xx 10^(23))`
Mass of the unitcell= ` ( 4 xx 60)/( 6.023 xx 10^(23))`
Densityof UINT cell = ` ("Mass of unit cell")/( " Volume of unit cell") `
` Rightarrow( 4 xx 60)/( 6.023 xx 10^(23)) xx 1/(64 xx 10^(-24))`
` Rightarrow6.2 g cm^(-3)`


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