# How do I find the formula of the compound given the ratio of its constituents by weight? [closed]

Problem : An organic compound containing carbon, nitrogen and oxygen will have a weight ratio $9:1:3$. The molecular weight of the compound is $108$. What is the formula of the compound?

I thought of calculating the empirical formula, but percentages are given for that, and not weight.

## closed as off-topic by orthocresol♦, Wildcat, M.A.R. ಠ_ಠ, Jan, Klaus-Dieter WarzechaAug 24 '16 at 9:31

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It's an algebra problem.

108 = 9x + 1x + 3x

Solve for x.

Weight of carbon per molecule = 9x Weight of nitrogen per molecule = 1x Weight of oxygen per molecule = 3x

Then convert from weights to numbers (I assume you know how to do that :) ).

Note that the result is rather nonsensical, as it gives you fractional atoms.

• The answer is given as $C_6H_8N_2$. – jimpix Aug 24 '16 at 13:29