3.12 Volumes of gases
5 exam questions worth 9 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is the volume of 2 moles of oxygen gas at room temperature and pressure?
Choose one answer.
Correct Not quite: the answer is 48 dm3
Mark scheme
C
Model answer
C: 2 × 24 = 48 dm3.
Calculate the volume, in dm3, of 3.2 g of methane, CH4, at RTP. (M_\mathrm{r} = 16)
Mark scheme
- moles = 3.2 ÷ 16 = 0.20 (1)
- volume = 0.20 × 24 = 4.8 dm3 (1)
Model answer
moles = 0.20, volume = 0.20 × 24 = 4.8 dm3
Magnesium reacts with excess hydrochloric acid: Mg + 2HCl → MgCl2 + H2
Calculate the volume of hydrogen, in cm3, produced from 0.48 g of magnesium at RTP. (A_\mathrm{r}: Mg = 24)
Mark scheme
- moles Mg = 0.48 ÷ 24 = 0.020 (1)
- moles H2 = 0.020 (1)
- volume = 0.020 × 24 000 = 480 cm3 (1)
Model answer
0.020 mol of Mg gives 0.020 mol of H2, which is 0.020 × 24 000 = 480 cm3.
Methane burns in oxygen: CH4 + 2O2 → CO2 + 2H2O
What volume of oxygen is needed to burn 50 cm3 of methane completely? (All volumes at the same temperature and pressure.)
Mark scheme
- 100 cm3 (1)
Model answer
The volume ratio is 1 : 2, so 50 cm3 of methane needs 100 cm3 of oxygen.
Explain why 1 mole of hydrogen and 1 mole of carbon dioxide occupy the same volume at RTP, even though their masses are very different.
Mark scheme
- both contain the same number of molecules (6.02 × 1023) (1)
- gas molecules are very far apart, so the size of the molecules does not affect the volume (1)
Model answer
Each contains the same number of molecules, and in a gas the molecules are so far apart that their size and mass make no difference to the volume.
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