# An elemental gas has a mass of 10.3 g. If the volume is 58.4 L and the pressure is 101 kPa at a temperature of 2.5 C, what is the gas?

May 17, 2017

Solving for $\text{molecular mass}$, we eventually identify the gas as $\text{helium}$.
If $n = \frac{P V}{R T}$, $\text{mass"/"molar mass} = \frac{P V}{R T}$
And so "molar mass"=(RTxx"mass")/(PV)
$= \frac{0.0821 \cdot \frac{L \cdot a t m}{K \cdot m o l} \times 10.3 \cdot g \times 275.5 \cdot K}{1 \cdot a t m \times 58.4 \cdot L} = 4.0 \cdot g \cdot m o {l}^{-} 1$, which molar mass is consistent with that of helium. (Note that is also consistent with ""^2H_2.)