A crystalline solid of a pure substance has a face-centred cubic structure with a cell edge of 400 pm. If the density of the substance in the crystal is 8 g cm^(-3), then the number of atoms present in 256 g of the crystal is Nxx10^24 . The value ofN is

A crystalline solid of a pure substance has a face-centred cubic struc

1.	A crystalline solid of a pure substance has a face-centred cubic structure with a cell edge of 400 pm. If the density of the substance in the crystal is 8 g cm^(-3), then the number of atoms present in 256 g of the crystal is Nxx10^24 . The value ofN is
Answer» Solution :`rho=(ZxxM)/(a^3xxN_0xx10^(-30))`where a is in pm and M in g `MOL^(-1)` `8=(4xxM)/((400)^3xx6xx10^23xx10^(-30))` or M=76.8 MOLES in 256 g =`256/76.8`=3.33 `THEREFORE` No. of atoms =`3.33xx6xx10^23=2xx10^24`