# NEET Chemistry The Solid State Questions Solved

BOARD

The well known mineral fluorite is chemically calcium fluoride. It is known that in one unit cell of this mineral there are 4 Ca2+ ions and 8 F- ions and that Ca2+ ions are arranged in a fcc lattice. The F- ions fill all the tetrahedral holes in the face centred cubic lattice of Ca2+ ions. The edge of the unit cell is 5.46$×$10-8 cm in length. The density of the solid is 3.18 g cm-3. Use this information to calculate Avogadro's number (Molar mass of CaF2 = 78.08 g mol-1).

Given :

Edge of the unit cell (a) = 5.46$×$10-8 cm

Density (P) = 3.18 g cm-3

According to the formula :

NA$\frac{Z×M}{{a}^{3}×P}$         $\therefore$ NA$\frac{4×78.08}{\left(5.46×{10}^{-8}{\right)}^{3}×3.18}$

$\therefore$ NA$\frac{3123.2}{517.612×{10}^{-23}}$   = 6.033$×$1023

Difficulty Level:

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