The Ideal Gas Law: Molar Mass Video Lessons

Concept: Molar Mass

# Problem: A 1.26 g gas sample occupies 651 mL at 31°C and 1.00 atm.What is the molar mass of the gas?

###### FREE Expert Solution

Molar mass:

First, we have to calculate the amount of gas in moles using the ideal gas equation.

$\overline{){\mathbf{P}}{\mathbf{V}}{\mathbf{=}}{\mathbf{n}}{\mathbf{R}}{\mathbf{T}}}$

P = pressure, atm
V = volume, L
n = moles, mol
R = gas constant = 0.08206 (L·atm)/(mol·K)
T = temperature, K

Isolate n (number of moles of gas):

$\frac{\mathbf{P}\mathbf{V}}{\mathbf{R}\mathbf{T}}\mathbf{=}\frac{\mathbf{n}\overline{)\mathbf{R}\mathbf{T}}}{\overline{)\mathbf{R}\mathbf{T}}}\phantom{\rule{0ex}{0ex}}\overline{){\mathbf{n}}{\mathbf{=}}\frac{\mathbf{P}\mathbf{V}}{\mathbf{R}\mathbf{T}}}$

Given:

V = 0.651 L

P = 1.00 atm
T = 31°C + 273.15 = 304.15 K
R = 0.08206 (L·atm)/(mol·K)

Calculate for n:

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###### Problem Details

A 1.26 g gas sample occupies 651 mL at 31°C and 1.00 atm.

What is the molar mass of the gas?