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# Help with moles/molecular mass question watch

1. Struggling to answer this question...

Compound F contains Carbon, Hydrogen and Oxygen only and contains Oxygen 54.2% oxygen by mass.
The molar mass of compound F is 118.0 gmol-1.
Show that the molecular formula of compound F is C4H6O4.

Any help is much appreciated.
2. OK.
So we know that the compound F has a molar mass of 118.0 gmol^-1.
If 54.2% of this is oxygen, surely 45.8% of this must be the remaining Carbon and Hydrogen.
So you need to calculate 45.8% of 118 and then try and figure out how many carbons and hydrogens can make up the remaining molar mass.
So when you do the above calculation(to give you the molar mass of Carbon + Hydrogen), you need to use a bit of trial and error to see how many times you could fit the atomic masses of Carbon or Hydrogen into the remaining mass.

Does that make sense?

Spoiler:
Show
118 x 0.458 = 54.044
Using the molar masses of Carbon and Hydrogen and a little bit of trial and error and you can figure out that 12 x 4 = 48 (4 carbons)
54-48 = 6
Therefore you have 6 hydrogens.
So if you total this up.
(12 x 4)+(6x1)+(16x4) = 118 gmol^-1

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