Ncert Exercises & Solutions

1.15 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.

Edge length, a = 3.61 × 10⁻⁸ cm
As the lattice is fcc type, the number of atoms per unit cell, z = 4
Atomic mass, M = 63.5 g mol⁻¹
We also know that, NA = 6.022 × 10²³ mol⁻¹

Applying the relation:

d = \frac{zM}{a^{3} N_{A}}

= \frac{4 \times 63.5 g {mol}^{- 1}}{{(3.61 \times 10^{- 8} cm)}^{3} \times 6.022 \times 10^{23} {mol}^{- 1}}

= 8.91 g {cm}^{- 3}

The measured value of density is given as 8.92 g cm⁻³. Hence, the calculated density 8.97 g cm⁻³ is in agreement with its measured value.

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