Question

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

• A. $12\text{u}$
• B. $14\text{u}$
• C. $18\text{u}$
• D. $28\text{u}$

Answer 1

The correct option is D $28\text{u}$

We know,
$1\text{u}=1.66054\times {10}^{-24}\text{g}$
Therefore, $14\text{g}=\frac{14}{1.66054\times {10}^{-24}}\text{u}$
$=8.431\times {10}^{24}\text{u}$
Given, $3.011\times {10}^{23}$ molecules of a gas weigh = $14\text{g}$
So molecular mass of the gas is $=\frac{8.431\times {10}^{24}}{3.011\times {10}^{23}}\text{u}$
$=28\text{u}$