5.00g of an unknown gas is collected at 20.0oC in a 1.00L container. It has a pressure of 2.733atm. What is the molar mass of the gas?

Answer 1

First you want to use the Ideal Gas Law to calculate the Moles of the Gas

PV = nRT

n = PV / RT

n = (2.733 atm x 1.00 L) / (0.08206 L*atm / mol*K * 293.15 K) = 0.1136 mol

Then to find the Molar Mass you want to take the given mass of the substance and divide by the number of moles

Molar Mass (M) = 5.00 g / 0.1136 mol = 44.01 g/mol

meaning that the molar mass of the unknown gas is approximately 44.01 g/mol

Answer 2

PV=nRT

You can substitute m/MM (mass/Molar Mass) for n and solve directly for MM in one step.

(2.733 atm)(1.00 L) = (5.00 g / (MM))(0.08206 Latm/molK)(20+273K)

rearrange for MM

MM = (5.00g)(0.08206 Latm/molK)(293K)/((2.733 atm)(1.00 L))

MM = 44.0 g/mol

(gas could be carbon dioxide)

Answer 3

PV = nRT ... Ideal Gas Law

Solving for moles (n), we have...

n = PV/RT

n = (2.733 atm)(1.00L)/(0.0821 Latm/Kmol)(293K)

n = 0.1136 moles

molar mass = g/mole = 5.00 g/0.1136 moles = 44.0 g/mole = molar mass