# NEET Chemistry The Solid State Questions Solved

BOARD

(a) What are intrinsic semi-conductors? Give an example.

(b) What is the distance between Na+ and Cl- ions in NaCl crystal if its density is 2.165 g cm-3? [Atomic mass of Na = 23u, Cl = 35.5u; Avogadro's number = 6.023$×$1023]

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Concept Questions :-

Density/Formula/packing fraction/ Semiconductors

(a) Intrinsic semi-conductors : These are insulators at room temperature and become semi-conductors when temperature is raised, Example : silicon and germanium.

(b) Applying the formula

$\rho$ = $\frac{ZM}{{a}^{3}×{N}_{A}}$, Z for NaCl is 4(fcc)

or a3$\frac{ZM}{\rho ×{N}_{A}}$ = $\frac{4×58.5}{2.165×6.023×{10}^{23}}$

a = $\sqrt[3]{\frac{4×58.5}{2.165×6.023×{10}^{23}}}$ = 564$×$10-10 cm

a = 2$×$ distance between Na+ and Cl- ions

$\therefore$ Distance between Na+ and Cl- ion

$\frac{564×{10}^{-10}}{2}$  = 282 pm.

Difficulty Level:

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