Question

$3.011\times {10}^{23}$ molecules of a gas weigh 14 g. Calculate the molecular mass of the gas.

• A. 12 u
• B. 14 u
• C. 18 u
• D. 28 u

Answer 1

The correct option is D 28 u

We know,
$1u=1.66054\times {10}^{-24}g$

Therefore, given mass in atomic mass unit is i.e.,
$14g=\frac{14}{1.66054\times {10}^{-24}}u=8.431\times {10}^{24}u$

Given, $3.011\times {10}^{23}$ molecules of a gas weighs 14 g i.e., $8.431\times {10}^{24}u$

So the mass of one molecule of gas i.e., molecular mass $=\frac{8.431\times {10}^{24}}{3.011\times {10}^{23}}u=28u$