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.

$\overline{){\mathbf{M}}{\mathbf{o}}{\mathbf{l}}{\mathbf{e}}{\mathbf{c}}{\mathbf{u}}{\mathbf{l}}{\mathbf{a}}{\mathbf{r}}{\mathbf{}}{\mathbf{W}}{\mathbf{e}}{\mathbf{i}}{\mathbf{g}}{\mathbf{h}}{\mathbf{t}}{\mathbf{}}{\mathbf{\left(}}{\mathbf{M}}{\mathbf{W}}{\mathbf{\right)}}{\mathbf{=}}\frac{\mathbf{g}}{\mathbf{m}\mathbf{o}\mathbf{l}}}$

**Step1**: 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): **

A sample of gas has a mass of 38.8 mg . Its volume is 226 mL at a temperature of 56 ^{o}C and a pressure of 860 torr .

Find the molar mass of the gas.

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Our tutors have indicated that to solve this problem you will need to apply the Ideal Gas Law Molar Mass concept. If you need more Ideal Gas Law Molar Mass practice, you can also practice Ideal Gas Law Molar Mass practice problems.