Question

5.60 g of an unknown gas at STP fills a 500 mL flask. What is the molar mass of the gas

Answer 1

Hey there!

From ideal gas equation we know,  PV = nRT

All the terms have their usual significance.

PV =w/M * RT

( where , n is number of moles = w/M,   we = weight of gas, M = molecular weight of the gas)

Therefore,  PV = wRT/M

At standard conditions ,  value of pressure, P = 1atm and standard temperature, T = 273K

And value of universal gas constant, R = 0.082 lit. atm. K⁻¹.mol⁻¹

Given that, weight of gas,

w = 5.60g and volume of gas,

V = 500mL = 0.5 Liters

Therefore, substituting all the value, we get   :

  Molar mass = 5.60 * 0.082 * 273 / 1 * 0.5

   Molar mass = 250.7232 g/mole