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Question
Copper crystallises into a fcc lattice with edge length 3.61 × 10−8 cm. Show that the calculated density is in agreement with its measured value of 8.92 g cm−3.
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Solution
Given: For fcc lattice, Z = 1 + 3 = 4 atoms
Edge length, a = 3.61 × 10−8 cm,
Atomic mass of Cu = 63.55 gm mo1−1
Avogadro’s number (NA) = 6.022 × 1023
To find: Density of Cu = ?
Formula: `rho = (Z xx M)/(a^3 xx N_A)`
= `(4 xx 63.55)/((3.61 xx 10^-8)^3 xx 6.022 xx 10^23`
= `254.2/(47.04 xx 10^-24 xx 6.022 xx 10^23)`
= `254.2/(283.27 xx 10^-1)`
= `254.2/28.327`
= 8.97 g cm−3
Thus, the calculated value is fairly in agreement with the measured value.
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