Calculate the number of oxygen molecules in 28 L of air

Air is composed of nitrogen (78%), oxygen (21%) and other gases (<1%). Knowing the percentage of oxygen in the air, we find the volume of oxygen.

V (O2) = 28 * 0.21 = 5.88 L

Dividing the volume of oxygen by the molar volume at normal conditions. (pressure – 1 atmosphere, temperature – 0 ° C), we get the amount of mol of oxygen.

Vm = 22.4 l

n (O2) = V / Vm = 5.88 / 22.4 = 0.26 mol

Multiply the number of moles of oxygen by Avogadro’s number Na and find the number of oxygen molecules in 28 liters of air.

Na = 6.02 * 10 ^ 23

N (O2) = n * Na = 0.26 * 6.02 * 10 ^ 23 = 1.57 * 10 ^ 23