The density of CaO is `3.35xx10^(3)kg*m^(3)`. This oxide crystallises in one of the cubic system with a = 480pm. Calculate the number of formula units in the unit cell of the oxide. Which type of cubic system is it?

Explanation

We know, `rho=(ZxxM)/(Nxxa^(3))`
Formula mass (M) of CaO = (40 + 16)`g*mol^(-1)=56g*mol^(-1)`
Given: `rho=3.35xx10^(3)kg*m^(-3)=3.35g*cm^(-3),a=480`pm
= `4.8xx10^(-8)cm`
`therefore" "Z=(rhoxxNxxa^(3))/M=(3.35xx6.022xx10^(23)xx(4.8xx10^(-8))^(3))/56=4`
Hence, number of formula units of CaO per unit cell = 4.
Therefore, it is a face-centred cubic system.