chemistry homework

Question

A  4.05 g sample of an unknown gas at 59 C and 1.05 atm  is stored in a 2.55 L flask.

What is the density of the gas?

what is the molar mass of the gas? 

Answer 1

The question asks for DENSITY, which has units of mass/volume, generally g/ml or g/L. We have been given both the mass (4.05 g) and the volume (2.55 L), so the density is simply 4.05g/2.55 L = 1.59 g/L

The question also asks for the molar mass of the gas, which has units of grams/mole. We have the grams (4.50 g), so we must find the number of moles. This can be done using the ideal gas law, PV = nRT.

P = pressure = 1.05 atm

V = volume = 2.55 L

n = number of moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in Kelvin = 59C + 273 = 332K

Solving for n, we have...

n = PV/RT = (1.05 atm)(2.55 L) / (0.0821 Latm/Kmol)(332K)

n = 0.0982 moles

molar mass = 4.05 g / 0.0982 moles = 41.2 g/mole