1.

An element with density 2.8 g cm^(-3) forms a fcc unit cell with edge length 4 xx 10^(-8) cm. Calculate the molar mass of the element. (Given : N_(A) = 6.022 xx 10^(23) mol^(-1))

Answer»

Solution :d = 2.8 g `CM^(-3)`, z = 4 (for FCC), a = 4 `XX 10^(-8)` cm, `N_(A) = 6.022 xx 10^(23) mol^(-1)`
`d = (Z xx M)/(N_(A) xx a^(3))`
`M = (d xx a^(3) xx N_(A))/(Z)`
`= (2.8 g cm^(-3) (4 xx 10^(-8) cm)^(3) xx 6.022 xx 10^(23))/(4)`
`M = 2.8 xx 16 xx 20^(-1) xx 6.022`
= 26.97 g `mol^(-1)`


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