# What is the percent composition by mass of aspartame C_14H_18N_2O_5?

Feb 19, 2016

I will solve for percentage composition of $N$ in the compound.

#### Explanation:

Molecular mass of aspartame:
$=$ $\left(14 \times 12.011 + 18 \times 1.00794 + 2 \times 14.011 + 5 \times 15.999\right) \cdot g \cdot m o {l}^{-} 1$

$=$ $294.31$ $g \cdot m o {l}^{-} 1$.

But we want the percentage composition of nitrogen in the sample:

$\frac{2 \times 14.011 \cdot g \cdot m o {l}^{-} 1}{294.31 \cdot g \cdot m o {l}^{-} 1}$ $\times$ 100% $=$ ??%

Note that the sum of the individual elemental percentages must equal 100%. Why??