Question

$11.2\text{L}$ of $C{H}_4$ and $22.4\text{L}$ of $C_2{H}_6$ at $STP$ are mixed. Then the correct statement(s) is/are:

• A. Vapour density of the mixture is 12.67
• B. Average molecular weight will be less than 16
• C. Average molecular weight will be greater than 16 and less than 30
• D. Average molecular weight will be greater than 30

Answer 1

Answer: (A), (C)

Average molecular weight will be greater than 16 and less than 30

Vapour density = the molecular mass / 2
At STP volume of one mole of gas $=22.4L$
Moles of methane = 0.5 i.e. 8 g of the gas
Moles of ethane = 1 i.e. 30g of the gas
Total mass of the gases = 8 + 30g
Molar mass of the mixture = $\frac{38}{1.5}=25.33g/mol$
Vapour density = 12.67