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1.18.   An element with molar mass  2.7\times 10^{-2}kg\; mol^{-1}  forms a cubic unit cell with edge length 405\; pm. If its density is 2.7\times 103\; kg\; m^{-3}, what is the nature of the cubic unit cell?

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We know that :

                           Density\ of\ unit\ cell = \frac{z.M}{a^3.N_A}

We are given :        Density = 2.7\times10^3\ Kg\ m^{-3}

and                        Molar\ mass = 2.7\times10^{-2}\ Kg\ mol^{-1}

and                      Edge\ length = 405 pm =4.05\times10^{-10}\ m

  So we need to find z (no. of atoms present in unit cell) by putting all values in formula of density.

 We get,                          z \approx 4.

It is known that face centred cubic also has 4 atoms in its unit cell, So given cubic unit cell is face centred.

Posted by

Devendra Khairwa

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