Question

1L of a gas at STP weighs 1.97g. What is molecular mass?

Answer 1

1 l = 1.97g
22.4 l = 22.4 * 1.97 = 44.128g

Answer 2

Answer : The molecular mass is, 44.154 g/mole

Solution : Given,

At STP,

Pressure = 1 atm

Temperature = 273 K

Using ideal gas equation,

$PV=nRT\\PV=\frac{m}{M}RT\\M=\frac{mRT}{PV}$

where,

P = pressure of the gas = 1 atm

V = volume of the gas = 1 L

m = mass of the gas = 1.97 g

T = temperature of the gas = 273 K

R = gas constant = 0.0821 Latm/moleK

M = molecular mass of the gas

Now put all the give values in the above formula, we get the molecular formula.

$M=\frac{(1.97g)\times (0.0821Latm/moleK)\times (273K)}{(1atm)\times (1L)}=44.154g/mole$

Therefore, the molecular mass is, 44.154 g/mole