Question

How many moles of helium are present in a 5 L container at STP?

Answer 1

A bit over a quarter of a mole.

Explanation:

The molar volume of an ideal gas at STP is `22.4*L`.

We assume, reasonably, the helium gas behaves ideally, and find that

`n_"He"` `=` `"Volume"/"Molar volume"` `=` `(5.0*L)/(22.4*L*mol^-1)` `=` `??mol`