Question on molecular mass (for an elemental analyssi)?

Question

A problem on a practice exam goes: The molecular mass of an organic compound is 190g/mol and the elemental analysis is 37.87% carbon, 11.68% hydrogen, and 50.45% oxygen by mass. The molecular formula of the compound is what?

It's multiple choice and after finding the number of each in the empirical formula, I got C3H11O3 -> But the choices on the multiple choice (that I didn't eliminate) are C3H11O3 and C6H22O6 - the answer key says the answer is C6H22O6 --

Did I do something wrong, or is there something I have to do to find the molecular formula from the empirical formula? The key probably lies in 190g/mol if I didn't do anything wrong... but what?

Thanks :-)

DanielHeyward · Accepted Answer

Empirical formula is not the actual molecular formula. You found the empirical formula as (C3H11O3)x and not C3H11O3.

Since the molecular mass is given as 190, you must calculate it on that basis.

That is x * {3*12 + 11*1 + 16*3} = 190.

Find the value of x. If x = 2, then you were wrong.

Anonymous · Answer

Your results are probably just a little off. It's normal, just include a percentage error.

Question on molecular mass (for an elemental analyssi)?

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