Question

a sample of a gas weighs 1.25g at 28°c occupying volume of 2.50×10^2 ml and its pressure is 715 torr .what is molar mass in grams?

Answer 1

Answer : The molar mass of gas is 131.269 g/mole.

Solution : Given,

Mass of gas = 1.25 g

Volume of gas = $2.50\times 10^2ml=0.25L$     (1 L = 1000 ml)

Pressure of gas = 715 torr

Temperature of gas = $28^oC=28+273=301K$      $(1^oC=273K)$

Gas constant, R = 62.364 L torr/mole K

Using ideal gas law,

$PV=nRT\\PV=\frac{W}{M}RT$

By rearranging the terms, we get

$M=\frac{WRT}{PV}$

where,

M = Molar mass of gas

W = Mass of gas

R = gas constant

T = temperature of gas

P = Pressure of gas

V = Volume of gas

Now put all the given values in above formula, we get the value of molar mass of gas.

$M=\frac{(1.25g)\times (62.364Ltorr/moleK)\times (301K)}{(715torr)\times (0.25L)}=131.269g/mole$

Therefore, the molar mass of gas is 131.269 g/mole.