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P4 General Studies: Air, Combustion and Rusting (Paper 2 (intermediate))
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 2 (intermediate))
Paper two links the shares of gases, ways of putting out fires and the speed of rusting.
Direct answers Find how much is lost first, then divide by the original total to get the share.
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 does a carbon dioxide extinguisher put out a fire?
- FoundationPutting a lid on a burning wok puts the fire out. Why?
- FoundationWhy does stainless steel rust less than ordinary iron?
- IntermediateNitrogen is about 78 per cent of air. How much nitrogen is there in 1 000 mL of air?
- IntermediateA sealed container starts with 300 mL of air and is left with 237 mL after burning. How much oxygen was used, and what share of the original volume is that?
- IntermediateFifteen of twenty nails in a damp jar rust after two weeks. What share rusted?
- ChallengeThe same nails rust in 48 hours when damp but take 240 hours when dry. How many times faster is rusting in damp air?
- ChallengeOxygen is about 21 per cent of air. How much oxygen is there in 2 500 mL of air?
- ChallengeA 20 g nail becomes 23 g after rusting. How much mass is gained, and what share is that?
- Error redoError clinic: a nail sealed in boiled distilled water will still rust. Is that right?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The carbon dioxide shuts the air away so the fuel gets no oxygen. | The gas blankets the flame and cools it a little; cutting off oxygen is the main effect. |
| 2 | The lid keeps air out, so the flame runs out of oxygen. | A lid stops fresh air entering, so the fire dies once the oxygen is used up; never use water. |
| 3 | It is an alloy whose surface forms a protective layer that keeps oxygen and water out. | Metals in the alloy form a tight oxide layer that separates the iron beneath from oxygen and water. |
| 4 | 780.0 mL. | One thousand multiplied by 78 and divided by 100 gives 780.0 mL. |
| 5 | 63 mL, which is 21.0 percentage points. | Three hundred minus 237 gives 63 mL; divided by 300 and multiplied by 100 that is 21.0 percentage points. |
| 6 | 75.0 percentage points. | Fifteen divided by twenty and multiplied by 100 gives 75.0 percentage points. |
| 7 | 5.0 times. | Two hundred forty divided by 48 gives 5.0, so rusting is 5.0 times faster when damp. |
| 8 | 525.0 mL. | Two thousand five hundred multiplied by 21 and divided by 100 gives 525.0 mL. |
| 9 | 3 g, which is 15.0 percentage points. | Twenty-three minus 20 gives 3 g, because the iron has joined with oxygen; 3 over 20 times 100 is 15.0 percentage points. |
| 10 | No. | Boiling drives the air out and sealing keeps new oxygen away, so the nail does not rust. |
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.
Then try paper three, using voltage and current to work out power and resistance.Tutor Registration →
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