Question

A unit cell of sodium chloride has four formula units. The edge length of the unit cell is $0.564$ nm. What is the density of sodium chloride? $[Na=23,Cl=35.5]$

• A. $1.16$ g$/c{m}^3$
• B. $2.62$ g$/c{m}^3$
• C. $2.16$ g$/c{m}^3$
• D. $3.16$ g$/c{m}^3$

Answer 1

Answer: (C)

$2.16$ g$/c{m}^3$

Let us consider the problem.

Using the formula

$\rho =\frac{N}{a^3}\frac{M}{N_A}$

We have

$\rho =\frac{4}{{\left(0.564\times {10}^{-7}cm\right)}^3}\times \frac{\left(58.5gmo{l}^{-1}\right)}{\left(6.023\times {10}^{23}mo{l}^{-1}\right)}=2.166gc{m}^{-3}$