Example 2 - Volume of Gas, Mass of Substance and Number of Particles

Question:
A gas jar containing 200cm³ of oxygen gas at s.t.p. Find the mass of the oxygen gas. [Relative atomic mass: Oxygen = 16; Molar volume of gas at s.t.p. = 22.4 dm³]

Answer:
Number of mole of oxygen gas, n = 200  cm 3 22400  cm 3 = 1 112  mol Relative molecular mass of oxygen = 2×16=32 Mass of oxygen = 1 112  × 32 gmol -1 =0.286g