The information that molar volume at STP of any gas is 22.4 dm3 is particularly important for knowing the number of moles, number of particles (i-e, atoms or molecules) and mass of the gas in a certain volume.
Number of moles can be calculated by dividing the given volume on the molar volume. Mathematically, if there is one mole in 22.4 dm3, there would be 2 moles in 44.8 dm3 at STP. Similarly, 0.5 moles in 11.2 dm3 at STP. This means,
Number of moles = (given volume)/22.4
Moreover, knowing the number of moles, number of particles can be calculated by multiplying the number of moles by 6.023 × 1023.
Knowing number of moles also makes possible to find the mass of the gas contained the given volume.
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