# How many molecules of aspirin (formula mass aspirin = 180 amu) are in a 0.250-gram sample?

May 15, 2018

Take the quotient...$\text{mass"/"molar mass}$...and,,,,

#### Explanation:

And so, for ${C}_{9} {H}_{8} {O}_{4}$ we gots a molecular mass of $180.16 \cdot g \cdot m o {l}^{-} 1$...

And so $\text{moles of aspirin} = \frac{0.250 \cdot g}{180.16 \cdot g \cdot m o {l}^{-} 1} = 0.001388 \cdot m o l$

And to get the number of molecules we simply multiply this molar quantity by the $\text{Avocado number}$....

$0.001388 \cdot m o l \times 6.02214 \times {10}^{23} \cdot m o {l}^{-} 1 = 8.36 \times {10}^{20}$ individual aspirin molecules....