Question

A density of gas is found to be 1.56gm/l and 745mm pressure at 65°c. Calculate the molecular mass of the gas

Answer 1

The formula applicable here is-
PM=dRT where..
P-pressure
M-molar mass
d-density
R-universal gas constant
T-temperature
from there M can be calculated as
M=dRT/P
=1.56×0.0821×338/745
(T-273+65)K
final answer will be
=0.058g

Answer 2

Answer: Molecular mass of the gas is 44.146 g/mol.

Explanation: We are given,

$Pressure=745 mmhg=\frac{745mmhg}{760mmhg/atm}=0.980atm$ (1 atm = 760 mmhg)

Density = 1.56 gm/L

Temperature = 65°C = (273+65)K = 338K

$R=0.8205\text{ L atm }mol^{-1}K^{-1}$

By using Gas equation, we get

PV = nRT

$P=\frac{nRT}{V}$       ....(1)

where, n = number of moles

Moles can be written as:

$\text{Number of Moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Putting Number of moles in equation 1, we get

$P=\frac{\text{(Given mass)}\times RT}{\text{(Molar mass)}\times V}$   ...(2)

Density can be written as:

$d=\frac{Mass}{volume}$

Putting this in equation 2, we get

$P=\frac{dRT}{M}$

Putting all the values in above equation, we get

$M=\frac{(1.56g/L)\times (0.08205\text{ L atm }mol^{-1}K^{-1})\times (338K)}{0.980atm}$

M = 44.146 g/mol.