# What is the mass of 5.306xx10^12 individual molecules of PCl_3?

Well for $5.306 \times {10}^{12}$ $\text{molecules}$ of $P C {l}_{3}$, we gots a $\text{nanogram}$ mass.
$\text{Mass"="Molar quantity"xx"molar mass} =$
$\left(5.306 \times {10}^{12} \cdot \text{molecules"xx137.33*g*mol^-1)/(6.022xx10^23*"molecules} \cdot m o {l}^{-} 1\right)$
$= 1 \cdot \text{ng}$