**Molar mass:**

$\overline{){\mathbf{Molar}}{\mathbf{}}{\mathbf{Mass}}{\mathbf{}}{\mathbf{\text{(MM)}}}{\mathbf{=}}\frac{\mathbf{g}}{\mathbf{mol}}}$

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:**

$\mathbf{P}\mathbf{=}\mathbf{975}\mathbf{}\overline{)\mathbf{mmHg}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{atm}}{\mathbf{760}\mathbf{}\overline{)\mathbf{mmHg}}}$

P = 1.2829 atm

V = 0.270 L

T = 88°C + 273.15 = 361.15 K

R = 0.08206 (L·atm)/(mol·K)

**Calculate for n:**

The mass of a sample of gas is 827 mg. Its volume is 0.270 L at a temperature of 88°C and a pressure of 975 mmHg. Find its molar mass.

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