What fraction of atoms in morphine is accounted for by carbon?

To determine the fraction of carbon in morphine, we need to know the chemical formula of morphine. From my readings, the chemical formula would be C17H19NO 3. We assume we have 1 g of this substance. Using the molar mass, we can calculate for the moles of morphine. Then, from the formula we relate the amount of carbon in every mole of morphine. Lastly, we multiply the molar mass of carbon to obtain the mass of carbon. We calculate as follows:

1 g C17H19NO 3 (1 mol / 285.34 g) (17 mol C / 1 mol C17H19NO3) (12.01 g C / 1 mol C) = 0.7155 g C

Fraction of carbon = 0.7155 g C / 1 g C17H19NO 3 = 0.7155