An alloy of copper and zinc solidifies in ccp structure, where copper occupies lattice points and zinc occupies 50% of the tetrahedral voids and all octahedral voids. Calculate the weight percentage of copper in the alloy. 

Explanation

Lattice points of fcc are,
corners of the cube (8) and centre of the faces (6) Number of copper atoms present in the unit cell `= (8xx(1)/(8))+(6xx(1)/(2))=1+3=4`
  Number of tetrahedral voids = 8 and
Number of octahedral voids = 4
Number of zinc atoms in the unit cell `=(8xx(50)/(100))+4=4+4=8`
Atoms of Cu and Zn are in the ratio, `4:8 = 1:2`
Mole ratio of the atoms of constituent elements of the alloy, Cu and Zn = 1:2
Mass of Cu = 63.5g.
Mass of `Zn=2xx64.5=129g`
Percentage weight of Cu `= ("weight of copper")/("weight of alloy")xx100`
`=(63.5)/(63.5+129)xx100=(63.5)/(192.5)xx100=33%`