Determine molecular formula for the headache remedy Ibuprofen?
Molar mass is 206 g/mol
precent composition 75.7% C, 8.80% H, 15.5% O
thanks so much im really having a rough time w/ chemistry
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If you assume a 100g sample of ibuprofen, it will contain:
75.7g C
8.80g H
15.5g O
If you convert those masses to moles (using each element’s molar mass) and use the moles as subscripts for each element, you will have a rough molecular formula. Divide all the subscripts through by the value of the smallest subscript, then multiply them all by an integer factor in order to convert them all to whole number subscripts.
[C(6.303)H(8.73)O(0.96875)]/(0.96875)
= C(6.506)H(9.0116)O(1)
= [C(6.506)H(9.0116)O(1)]*2
= C(13.012)H(18.023)O(2)
= C13H18O2
And you can check your answer with Wikipedia (source link). It’s actually pretty reliable for science and math topics.
Calculate the moles of C, H, and O in 100 grams:
75.7 g C / 12.011 g/mol = 6.303 mol C atoms
8.80 g H / 1.008 g/mol = 8.730 mol H atoms
15.5 g O / 16.00 g/mol = 0.969 mol O atoms
Determine the ratio of O:C:H by dividing by the smallest
C: 6.303 / 0.969 = 6.5
H: 8.730 / 0.969 = 9.0
O: 0.969/0.969 = 1.0
Multiply all by 2 so that you have whole numbers-
C = 2×6.5 = 13
H = 2×9.0 = 18
O = 2×1 = 2
Empirical formula = C13H18O2 (molar mass = 206)
Therefore the empirical formula is the molecular formula