The Ideal Gas Law: Molar Mass Video Lessons

Concept: Molar Mass

# Problem: An unknown gas contained in a 1.85 L flask is weighed and found to have a mass of 15.87 g at a pressure of 2.45 atm and a temperature of 18.6°C. What is the molecular weight of the gas?a. 5.35 g/molb. 83.8 g/molc. 1.14 g/mold. 155 g/mole. 77.1 g/mol

###### FREE Expert Solution
81% (481 ratings)
###### FREE Expert Solution

We’re being asked to determine the molecular weight of the unknown gas.

Recall that molecular weight is in grams per 1 mole of a substance.

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):

81% (481 ratings)
###### Problem Details

An unknown gas contained in a 1.85 L flask is weighed and found to have a mass of 15.87 g at a pressure of 2.45 atm and a temperature of 18.6°C. What is the molecular weight of the gas?

a. 5.35 g/mol

b. 83.8 g/mol

c. 1.14 g/mol

d. 155 g/mol

e. 77.1 g/mol

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Based on our data, we think this problem is relevant for Professor Bindell's class at UCF.