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A substance f...

Question

A substance forms face-centred cubic crystals. Its density is $1.984 g c m^{- 3}$ and the edge length of the unit cell is $630 p m$ . Calculate the molar mass of the substance.

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Solution

$ρ = \frac{Z \times M_{A}}{N_{A} \times a^{3}}$
$Z = 4$ (for FCC), $ρ = 1.984 g / c m^{3}$ , $M_{A} = ?$ , $a = 6.3 ˚ A$
$1.984 = \frac{4 \times M_{A}}{6.023 \times 10^{23} \times 250 \times 10^{- 24}}$
$M_{A} = 75$ $a m u$

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