中文（繁體）
中文（简体）
English
S4 Chemistry: Molar Volume and Gas Calculations (Paper 3: Challenge)
S4 Chemistry: Molar Volume and Gas Calculations (Paper 3: Challenge)
Ten questions combining molar volume: combustion volume ratios, density to relative molecular mass, yield, converting between 22.4 and 24, and formula from combustion data, with answers.
Direct answers Answers in order: 9.6 dm3 and 4.8 dm3, 30.0, 86.1 percent, 0.25 mol and 6.0 dm3, 1 to 1 and 16 to 1, 6.4 g, C3H8, 3.0 dm3 of hydrogen left, 3.69 dm3, 24 dm3 of any gas is 1 mol.
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)
- FoundationMethane burns as CH4 + 2O2 giving CO2 + 2H2O. What volume of oxygen is needed for 4.8 dm3 of methane and what volume of carbon dioxide forms?
- FoundationA gas has a density of 1.25 g/dm3 at room temperature and pressure. What is its relative molecular mass?
- FoundationDecomposing 0.15 mol of calcium carbonate should release 3.6 dm3 of carbon dioxide, but only 3.1 dm3 is collected. What is the percentage yield?
- IntermediateHow many moles are there in 5.6 dm3 of gas at s.t.p. with a molar volume of 22.4 dm3/mol, and what volume does the same sample occupy at room conditions?
- IntermediateAt the same temperature and pressure, what are the ratios of molecule number and of mass for equal volumes of oxygen and hydrogen?
- IntermediateA 4.8 dm3 mixture of carbon monoxide and carbon dioxide contains 0.20 mol in total, of which 0.05 mol is carbon dioxide. What is the mass of the mixture?
- ChallengeBurning 0.10 mol of a hydrocarbon gives 0.30 mol of carbon dioxide and 0.40 mol of water. What is its molecular formula?
- Challenge9.0 dm3 of hydrogen is sparked with 3.0 dm3 of oxygen. Which gas is left over and what volume remains?
- Challenge10.0 g of zinc reacts with excess dilute hydrochloric acid as Zn + 2HCl giving ZnCl2 + H2. What volume of hydrogen is obtained at room conditions, with Zn equal to 65?
- Error redoA student says that 24 dm3 of any gas at room temperature and pressure is 1 mol of oxygen. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 9.6 dm3 of oxygen and 4.8 dm3 of carbon dioxide | 4.8 dm3 is 0.20 mol, the coefficient of oxygen gives 0.40 mol or 9.6 dm3, and the coefficient of carbon dioxide gives 4.8 dm3. |
| 2 | 30.0 | One mole occupies 24 dm3, so its mass is 1.25 times 24 or 30.0 g, and the relative molecular mass is 30.0. |
| 3 | 86.1 percent | The yield is the actual over the theoretical volume, and 3.1 divided by 3.6 gives 0.861, that is 86.1 percent. |
| 4 | 0.25 mol, which occupies 6.0 dm3 at room conditions | 5.6 divided by 22.4 is 0.25 mol, and the same moles multiplied by 24 give 6.0 dm3 at room conditions. |
| 5 | Molecule ratio 1 to 1 and mass ratio 16 to 1 | Equal volumes mean equal moles, so the molecule numbers match, while the mass ratio follows the relative molecular masses of 32 and 2. |
| 6 | 6.4 g | The 0.15 mol of carbon monoxide weighs 4.2 g and the 0.05 mol of carbon dioxide weighs 2.2 g, giving 6.4 g together. |
| 7 | C3H8 | Each mole of the hydrocarbon contains 3 mol of carbon atoms and 8 mol of hydrogen atoms, so the formula is C3H8, propane. |
| 8 | The oxygen is used up and 3.0 dm3 of hydrogen remains | There are 0.375 mol of hydrogen and 0.125 mol of oxygen; the two to one reaction needs only 0.25 mol or 6.0 dm3 of hydrogen, leaving 3.0 dm3. |
| 9 | 3.69 dm3 | 10.0 divided by 65 gives 0.1538 mol of zinc, each mole of zinc releases one mole of hydrogen, and multiplying by 24 gives 3.69 dm3. |
| 10 | Wrong. Any gas at 24 dm3 is 1 mol, but it need not be oxygen, since the gas identity does not set the volume. | The molar volume depends on temperature and pressure rather than on the molecules, so only the number of moles can be deduced. |
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.
Decide first whether the question gives mass, moles or volume, then convert everything to moles.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.