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Question
Calculate the number of unit cells in 8.1 g of aluminium if it crystallizes in a f.c.c. structure. (Atomic mass of Al = 27 g mol–1)
Solution
Given,
Mass of Al = 8.1
Atomic mass of Al = 27 g mol-1
Number of atoms = number of moles × 6.022 × 1023 = `8.1/27` × 6.022×1023
= 0.3 × 6.022 × 1023
= 1.8066×1023
As one fcc unit cell have 4 atoms
Hence number of unit cells having 1.8066×1023 atoms = `(1.8066 xx 10^23)/4 = 4.51 xx 10^22` unit cell
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