Question

The unit cell length of sodium chloride crystal is 564 pm. Its density would be:

• A. (A) 1.082 g cm−3
• B. (B) 2.165 g cm−3
• C. (C) 3.247 g cm−3
• D. (D) 4.330 g cm−3

Answer 1

Answer: (B)

(B) 2.165 g cm−3

Answer 2

Explanation:
Given:a=564pm=564×10−10cmWe know that:The density is given by the formula:ρ=zMa3NAAs we know that,Each unit cell of NaCl has 4Na−and 4Cl−ions.⇒z=4Avogadro's number, NA=6.022×1023/molThe total mass of NaCl:M=22.99+34.34=58.5 g/molTherefore,Density, ρ=zMa3NA=4×58.5(564×10−10)3×6.022×1023 g cm−3=2.165 g cm−3Hence, the correct option is (B).