It is known that the density of oxygen is 1.429g/l and that of air is 1.293g/l. The mass fraction of oxygen in air (density = mass / volume) is calculated

Let the volume of air be 1L, because the volume fraction of oxygen in air is 21%, so the volume of oxygen is 0.21l, the mass of air = 1L × 1.293g/l = 1.293g, the mass of oxygen = 0.21l × 1.429g/l = 0.3g, so the mass fraction of oxygen in air = 0.3g1.293g × 100% ≈ 23.2%

It is known that the air density under standard condition is 1.293 g / L, the oxygen density is 1.429 g / L, and the air under existing standard condition is 1 000 ml. the mass of oxygen is calculated

Under the standard condition, the air density of 1.293g / L is the interference data, and mo2 = 1L × 21% × 1.429g / L = 0.30009g ≈ 0.3g
What should be investigated is Avogadro's law

It is known that the density of air and oxygen under standard atmospheric pressure is 11.923 g / L and 1.429 g / L respectively. The mass fraction is calculated according to the volume fraction of oxygen in the air

Let air volume be 1 L, then air mass = 1.293 G
If the oxygen volume in air is 21%, the oxygen volume is 1L × 21%
The oxygen mass is 1 L × 21% × 1.429 g / L = 0.3 g / L
Oxygen mass fraction = 0.3 g △ 1.293g = 23.2%

It is known that the density of oxygen is 1.429g/l and that of air is 1.293g/l. The mass fraction of oxygen in air (density = mass / volume) is calculated