What is the mass of 7.9 * 10^23 of O_2 at STP?

Jan 30, 2016

The mass of $7.9 \times {10}^{23}$ ${O}_{2}$ molecules is INDEPENDENT of temperature and pressure. It is approx. $40$ $g$.

Explanation:

Avogadro's number of ${O}_{2}$ molecules has a mass of $32.00$ $g$.

We have $7.9 \times {10}^{23}$ ${O}_{2}$ particles; i.e.

$\left(7.9 \times {10}^{23} \text{ particles")/(6.022xx10^23" particles } m o {l}^{-} 1\right)$ $= 1.31$ $m o l$.

So we take this molar quantity, and multiply this by the molecular weight:

$1.31 \cdot m o l \times 32.00 \cdot g \cdot m o {l}^{-} 1$ $=$ ??? g