A gas sample contains 4.00g of CH4 and 2.00g of He. What is the volume of the sample at STP?

As we know that 1 mole of any gas when acting perfectly / ideally occupies 22.4 L of volume.

It means that in order to calculate volume occupied both by CH₄ and He, we must calculate their moles.

Hence,

Moles are given as,

Moles = Mass / Mass

Moles of CH₄;

Mole-CH₄ = 4 g / 16 g. mol⁻¹

Mole-CH₄ = 0.25 mol

Moles of He;

Mole-He = 2 g / 4 g. mol⁻¹

Mole-He = 0.5 mol

Now adding moles of both gases,

= 0.25 + 0.5

= 0.75 mol

Therefore, when,

1 mole of gas occupy = 22.4 L of Volume

Then,

0.75 mol will occupy = X L of Volume

Solving for X,

X = (0.75 mol * 22.4 L) : 1 mole

X = 16.8 L