Calculating the volume of a certain number of moles
4 marks · NormalAnswer the questions about gases at room temperature and pressure (rtp).
State the volume occupied by 1 mole of any gas at rtp in dm³.
State the volume occupied by 1 mole of any gas at rtp in cm³.
Is the volume occupied by 1 mole of a gas at rtp the same for all gases? Give a reason for your answer.
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(a) 24 dm³
(b) 24,000 cm³
(c) Yes, because 1 mole of any gas contains the same number of molecules and occupies the same volume at rtp. · must show States volume is same for all gases, States reason: same number of molecules per mole
Common mistakes: Mixing up units for molar volume; Incorrect explanation (e.g. referring to mass or molecular weight only)
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Marking points
B1 (a) · 1 mark · States 24 dm³ as the molar volume at rtp.
B2 (b) · 1 mark · States 24,000 cm³ as the molar volume at rtp.
B3 (c) · 1 mark · States the volume is the same for all gases.
B4 (c) · 1 mark · Gives a correct reason: 1 mole of any gas contains the same number of molecules.
Worked solution
a) 1 mole of a gas at rtp occupies 24 dm³.
b) 1 mole of a gas at rtp occupies 24,000 cm³.
c) Yes, because 1 mole of any gas contains the same number of molecules, so occupies the same volume at rtp.