Question

Van der waals constant "b" of helium is $24mLmo{l}^{-1}$. Find molecular diameter of helium.

• A. $1.335\times {10}^{-10}cm$
• B. $1.35\times {10}^{-8}cm$
• C. $2.67\times {10}^{-8}cm$
• D. $4.34\times {10}^{-8}cm$

Answer 1

The correct option is C

$2.67\times {10}^{-8}cm$

b = 4 $\times$ volume occupied by molecules of 1 mole of a gas ,

or b = $4N_A⟮\frac{4}{3}\pi r^3⟯$

or r = $⟮\frac{3b}{16N_A\pi }⟯$

= $⟮\frac{3\times 24}{16\times 6.023\times {10}^{23}\times 3.14}{⟯}^{\frac{1}{3}}cm$

= 1.355 $\times {10}^{-8}$ cm.