Question

Calculate the vapour density of a gas, 12.8g of which occupies 10L at a pressure of 750 mm at 27°C.

Answer 1

In order to calculate the vapour density of any gas, we need its molar mass.

According to the question, the weight of the gases, pressure and temperature is also given, we need to calculate the number of moles of the given gas using the ideal gas equation,

                                                    PV = nRT

The number of moles is calculated and the weight of the given gas is used therefore, we can calculate the molecular mass.  

$vapour\quad density\times 2 =$ molecular mass

                                                      PV=nRT

$n=\frac{PV}{RT}=\frac{750}{760}.\frac{10}{0.0821}\times300 =0.4moles$

0.4 moles = 12.8g

1mole = 32g

2(VD) = molar mass

Vapour density,

VD=$\frac{32}{2}=16$