Using the molar volume in calculations with chemical equations

2 marks · Hard

A student collects 8.4 g of oxygen gas at room temperature and pressure (rtp). Calculate the volume, in dm³, of this oxygen gas. (Ar: O = 16; molar volume = 24 dm³ at rtp.)

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

2.52 dm³ (±0.02)

Also accept: 2.5 dm³; 2.52; 2.50

Common mistakes: Forgetting to divide by the Mr for O2; Using cm³ instead of dm³; Not keeping significant figures

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Calculate number of moles: (accept 0.26 or 0.263)

A1 · 1 mark · Correct volume: ; final answer should be about 6.3 dm³ (ECF from wrong moles possible) [ERROR: Correction: 8.4/32=0.2625, 0.2625×24=6.3, not 2.52. The correct value is 6.3 dm³! Change to finalAnswer: '6.3 dm³', accepted alternatives: '6.30', '6.31'] (follow-through)

Worked solution

Calculate moles of oxygen:

Calculate volume of gas using molar volume at rtp:

Final answer: 6.3 dm³