1.

Copper crystallises with face-centred cubic unit cell. If the radius of copper atom is 127.8 pm, calculate the density of copper metal. (Atomic mass of Cu = 63.55 g/mol and Avogadro's number N_(A) = 6.02 xx 10^(23) mol^(-1))

Answer»

Solution :fcc `rarr` 4 atoms = Z
r = 127.8 pm
`r = (a)/(2 sqrt(2))`
`therefore""a = 127.8 xx 2 sqrt(2)`
= 361.47 pm
`d = (Z xx M)/(a^(3) xx N_(A))`
`d = (4 xx 63.55 G MOL -1 )/((361.47 xx 10^(-12)m)^(3) xx 6.02 xx 10^(23) mol^(-1))`
= 8.9 `gm^(-3)`


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