# Problem: What is the molar mass of an unknown hydrocarbon whose density is measured to be 1.97 g/L at STP?

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###### FREE Expert Solution

We’re asked to determine the molar mass of an unknown hydrocarbon whose density is measured to be 1.97 g/L at STP.

Recall that we can use the ideal gas equation to find the density of a gas (hydrocarbons usually exist as a gas at STP):

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

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

###### Problem Details

What is the molar mass of an unknown hydrocarbon whose density is measured to be 1.97 g/L at STP?