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S4 Chemistry: Molar Volume and Gas Calculations (Paper 2: Intermediate)
S4 Chemistry: Molar Volume and Gas Calculations (Paper 2: Intermediate)
Ten questions applying the molar volume to reactions: mass from volume, gas mixtures, limiting reagents and volume ratios from equations, with answers.
Direct answers Answers in order: 1.5 mol, 88 g, 12 dm3, 30, 1.5 times 10 to the 23, 2.4 dm3, 18 dm3 and 12 dm3, oxygen limiting and 24 dm3, 18 dm3, volume ratio is the mole ratio.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 Chemistry: Molar Volume and Gas Calculations |
| Level | S4 |
02 Questions (10 items)
- FoundationHow many moles are there in 36 dm3 of gas at room temperature and pressure?
- FoundationWhat is the mass of 48 dm3 of carbon dioxide at room temperature and pressure, with CO2 equal to 44?
- Foundation0.20 mol of nitrogen is mixed with 0.30 mol of oxygen. What is the total volume at room temperature and pressure?
- IntermediateA gas of mass 3.0 g occupies 2.4 dm3 at room temperature and pressure. What is its relative molecular mass?
- IntermediateHow many molecules are there in 0.25 mol of gas, taking the Avogadro constant as 6.0 times 10 to the 23 per mole?
- IntermediateWhat volume of carbon dioxide at room conditions is released when 10 g of calcium carbonate decomposes completely, with CaCO3 equal to 100?
- ChallengeNitrogen and hydrogen combine as N2 + 3H2 giving 2NH3. What volume of hydrogen is needed for 6.0 dm3 of nitrogen and what volume of ammonia forms?
- Challenge4.0 g of hydrogen and 16 g of oxygen are burned. Which is the limiting reagent and what volume of hydrogen is actually used?
- ChallengeIn the electrolysis of water, 2H2O giving 2H2 and O2, what volume of oxygen is collected together with 36 dm3 of hydrogen?
- Error redoA student claims the volume ratio in a gas reaction equals the mass ratio. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 1.5 mol | 36 divided by 24 gives 1.5 mol. |
| 2 | 88 g | 48 divided by 24 is 2.0 mol, and 2.0 times 44 gives 88 g. |
| 3 | 12 dm3 | Adding the moles gives 0.50 mol, and multiplying by 24 gives 12 dm3. |
| 4 | 30 | 2.4 divided by 24 is 0.10 mol, and 3.0 divided by 0.10 is 30. |
| 5 | 1.5 times 10 to the 23 | The number of molecules is the moles multiplied by the Avogadro constant and does not depend on the gas. |
| 6 | 2.4 dm3 | 10 divided by 100 is 0.10 mol of calcium carbonate and each mole releases one mole of gas, giving 2.4 dm3. |
| 7 | 18 dm3 of hydrogen and 12 dm3 of ammonia | At the same temperature and pressure the volume ratio equals the ratio of coefficients, one to three to two, so 6.0 dm3 is scaled by three and by two. |
| 8 | Oxygen is limiting and 24 dm3 of hydrogen is used | There are 2.0 mol of hydrogen and 0.50 mol of oxygen; the equation needs a ratio of two to one, so the oxygen can only use 1.0 mol of hydrogen, that is 24 dm3. |
| 9 | 18 dm3 | 36 dm3 of hydrogen is 1.5 mol, so the oxygen is half of that at 0.75 mol, which multiplied by 24 gives 18 dm3. |
| 10 | Wrong. At the same temperature and pressure the volume ratio equals the mole ratio, not the mass ratio, which needs each relative molecular mass. | Hydrogen and oxygen react in a volume ratio of two to one but a mass ratio of 4 to 32, so the two ratios are quite different. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Use two lines of rough work per question, one for the equation and one for the moles.Tutor Registration →
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