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Lead sulfide has fcc structure. The edge length of the unit cell of PbS crystal is 500 pm What is its density ? |
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Answer» Solution :MOLECULAR mass of PBS = 207.2+32 = 239.2 Edge length, a = 500 , pm NUMBER of molecules per unit cell, Z=4 (for fcc structure) Density of unit cell, `d= (Zxx M)/(N_A XX a^3 xx 10^(-30)) g cm^(-3)` `therefore d = (4xx239.2 g "mol"^(-1))/(6.022 xx 10^(23) "mol"^(-1) xx (500)^3 xx 10^(-30) cm^3)` `= (956.8)/(75.275) g cm^(-3) = 12.7 g cm^(-3)` |
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