A chem problem. Don't know how to start.

kirby · **Joined:** Wed, 24 Sep 2008 04:29:36 UTC **Posts:** 13

A hydrocarbon mixture contains an acid and another unidentified component. The mass fraction of the acid is 0.387 while its mole fraction is 0.317. The molecular weight of the acid is 60.05. What is the molecular weight of the other unidentified component.

I don't how to begin doing the question. Help would be appreciated.

outermeasure · **Posted:** Sun, 8 Mar 2009 15:26:35 UTC

kirby wrote:

A hydrocarbon mixture contains an acid and another unidentified component. The mass fraction of the acid is 0.387 while its mole fraction is 0.317. The molecular weight of the acid is 60.05. What is the molecular weight of the other unidentified component.

I don't how to begin doing the question. Help would be appreciated.

Set it up as a table

$\begin{tabular}{|c|c|l|} \hline \text{Acid}&\text{Unidentified}&\text{(Reason)}\\ \hline\hline 0.317\,\mathrm{mol} & 0.683\,\mathrm{mol}&\text{mole fraction}\\ 0.317\times 60.05\,\mathrm{g} & 0.683\,\mathrm{mol}&\text{using molecular mass of acid}\\ 0.387\,\mathrm{g} & 0.613\,\mathrm{g}&\text{mass fraction}\\ 0.317\times 60.05\,\mathrm{g} & 0.317\times 60.05\times (0.613/0.387)\,\mathrm{g}&\text{multiply up}\\ \hline \end{tabular}$
So from the last row and the middle row, 0.683 moles of the unidentified substance weighs 0.317*60.05*(0.613/0.387) grammes, so molecular weight of the unidentified component is ...

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A chem problem. Don't know how to start.

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