Answer:
2.69x10²² molecules of O₂
Explanation:
We start with the knowldge that says: "the sum of mole fractions in a mixture of gases = 1 ". When we start with this, we propose
Mole fraction N₂ + Mole fraction Ne + Mole fraction O₂ = 1
0.55 + 0.25 + Mole fraction O₂ = 1
Mole fraction O₂ = 1 - 0.25 - 0.55 → 0.20
We know that the mixture is at STP in a 5L of volume, so let's calculate the volume. We use the Ideal Gases Law
1 atm . 5L = n . 0.082 . 273 K
n = 1 atm . 5L / 0.082 . 273K → 0.223 moles
These number of moles are the total moles in the mixture. We apply the mole fraction to determine the moles of O₂ that are present in the container.
Mole fraction O₂ = Moles O₂ / Total moles → Mole fraction O₂ . Total moles = moles O₂
0.223 moles . 0.2 = 0.0446 moles of O₂
Let's count the number of molecules
0.0446 moles . 6.02x10²³molecules / 1 mol = 2.69x10²² molecules of O₂
