Recall that mass percent is given by:

$\overline{){\mathbf{\%}}{\mathbf{}}{\mathbf{mass}}{\mathbf{=}}\frac{\mathbf{mass}\mathbf{}\mathbf{of}\mathbf{}\mathbf{X}}{\mathbf{total}\mathbf{}\mathbf{mass}}{\mathbf{\times}}{\mathbf{100}}}$

Assuming we have 100 g of the compound, this means we have 40.00 g C, 6.72 g H, and 53.28 g O.

Now, we need to get the moles of each element in the compound.

The atomic masses are 12.01 g/mol C, 1.01 g/mol H, and 16.00 g O.

$\mathbf{40}\mathbf{.}\mathbf{00}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{C}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{C}}{\mathbf{12}\mathbf{.}\mathbf{01}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{C}}}$ **= 3.33 mol C**

$\mathbf{6}\mathbf{.}\mathbf{72}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{H}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{H}}{\mathbf{1}\mathbf{.}\mathbf{01}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{H}}}$** = 6.65 mol H**

$\mathbf{53}\mathbf{.}\mathbf{28}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{O}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{O}}{\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{O}}}$** = 3.33 mol O**

Divide the number of moles of each by the smallest value.

Fructose is a common sugar found in fruit. Elemental analysis of fructose gave the following mass percent composition: C 40.00%, H 6.72%, O 53.28%. The molar mass of fructose is 180.16 g/mol.

Find the molecular formula of fructose.

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