Question

What is the density of potassium, if it has bcc structure with edge length $4\mathring{A}$ ? (Atomic mass of $K=39$ )

• A. $3gc{m}^{-3}$
• B. $2gc{m}^{-3}$
• C. $5gc{m}^{-3}$
• D. $4gc{m}^{-3}$

Answer 1

Answer: (B)

For density, $\rho =\frac{z\times M}{a^3\times N_A}$
Edge length, $a=4\mathring{A}=4\times 10^{-8}cm$
For bcc structure, $Z=2$
$\rho =\frac{2\times 39}{{\left(4\times 10^{-8}\right)}^3\times 6.022\times 10^{23}}$
$=0.202\times 10^{24}\times 10^{-23}gc{m}^{-3}$
$=0.202\times 10gc{m}^{-3}=2.02gc{m}^{-3}$