中文（繁體）
中文（简体）
English
P4 General Studies: Air, Combustion and Rusting (Paper 3 (challenge))
Tutor Prep Guide · the make-up of air and oxygen, burning needing oxygen and how fires are put out, the two conditions for rusting, rust prevention and the mass gained by rust
P4 General Studies: Air, Combustion and Rusting (Paper 3 (challenge))
Paper three asks you to work back from the water rise to the share of oxygen and to compare rusting speeds.
Direct answers Decide whether the question is about oxygen, nitrogen or rust mass first, then use the matching formula.
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: P4 General Studies: Air, Combustion and Rusting |
| Level | parts of a closed circuit, conductors against insulators, series against parallel, adding up battery voltage, and electrical safety |
02 Questions (10 items)
- FoundationWhy might you lower a lighted candle into a long-closed cellar first?
- FoundationWhy does iron near the sea or in salt water rust so quickly?
- FoundationAfter burning inside a bell jar the water rises by about a fifth of the volume. What does that show?
- IntermediateBurning in a 500 mL bell jar makes the water rise 105 mL. What share of the air is oxygen?
- IntermediateA 40 g iron piece weighs 48 g after rusting. What is the increase in percentage points?
- IntermediateTwenty-seven of thirty-six rust-prevention methods work. What share is effective?
- ChallengeBurning uses up oxygen in 500 mL of air and leaves 395 mL. How much was used, and roughly how much nitrogen remains?
- ChallengeA nail takes 30 days to rust in a dry box but only 5 days near salt water. How many times faster is that?
- ChallengeOxygen inside the jar falls from 21 per cent to almost none. How many percentage points are lost, and why can the remaining gas no longer support burning?
- Error redoError clinic: the rise in water level equals both the oxygen used and the amount of nitrogen. Is that right?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | If the candle goes out, oxygen is too low and people must stay out. | A closed space may be short of oxygen or hold too much carbon dioxide; the flame is the simplest test. |
| 2 | Salt water conducts electricity, speeding up corrosion, and both water and oxygen are plentiful. | Salt makes the water conduct better so corrosion runs faster, which is why iron near boats and the shore needs extra protection. |
| 3 | Oxygen is about 21 per cent of air, and water fills the space it leaves. | A fifth is about 20 per cent, close to the share of oxygen, so the rise estimates how much oxygen was there. |
| 4 | 21.0 percentage points. | One hundred five divided by 500 and multiplied by 100 gives 21.0, matching the usual 21 per cent oxygen. |
| 5 | 20.0 percentage points. | Forty-eight minus 40 gives 8 g; 8 over 40 times 100 is 20.0 percentage points. |
| 6 | 75.0 percentage points. | Twenty-seven divided by thirty-six and multiplied by 100 gives 75.0 percentage points. |
| 7 | 105 mL used; about 390.0 mL of nitrogen. | Five hundred minus 395 gives 105 mL; nitrogen is 78 per cent, and 500 times 0.78 is 390.0 mL. |
| 8 | 6.0 times. | Thirty divided by 5 gives 6.0, so it is 6.0 times faster. |
| 9 | About 21.0 percentage points are lost; the rest is mostly nitrogen, which does not support burning. | Twenty-one minus zero leaves about 21.0 percentage points; nitrogen is unreactive, so the flame dies. |
| 10 | No. | The rise only shows the oxygen used; nitrogen stays in the jar and takes about 78 per cent. |
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.
Paper four clears the conductor, insulator and battery direction misconceptions.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.