S2 Science: Combustion, Oxidation And Mass (Paper 2 (intermediate))

S2 Science: Combustion, Oxidation and Mass (Paper 2 (intermediate))

2026-11-14

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Tutor Prep Guide · The three conditions for burning, extinguishing methods, tests for carbon dioxide and oxygen, oxidation of magnesium and iron, complete and incomplete combustion, conservation of mass and calculating product masses

S2 Science: Combustion, Oxidation and Mass (Paper 2 (intermediate))

This paper focuses on the composition of air, tests for oxygen and hydrogen, the conditions and accelerators of rusting, the water rise in the bell jar experiment, and calculations on oxygen in air, mass gained on rusting and the products of burning methane.

Direct answers　Oxygen is about one fifth of air; a relighting splint means oxygen; hydrogen burns with a pop and forms water; rusting needs oxygen and water and is faster with salt; the bell jar water rises one fifth, the volume of oxygen; 250 cm³ of air holds 52.5 cm³ of oxygen; 5.00 g rising to 5.62 g is a 12.4 percent gain; 8 g of methane gives 22 g of carbon dioxide.

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: S2 Science: Combustion, Oxidation and Mass
Level	S2

02　Questions (10 items)

FoundationAbout how much of the air is oxygen?
FoundationHow do you test that a gas jar holds oxygen?
FoundationWhat sound and product are seen when hydrogen burns?
IntermediateWhy does the mass of steel wool increase when it rusts?
IntermediateWhy does salt water speed up rusting?
IntermediateWater rises inside a bell jar after a candle burns out. What does this show?
ChallengeAbout how much oxygen is in 250 cm³ of air?
ChallengeSteel wool goes from 5.00 g to 5.62 g on rusting. What is the gain and the percentage gain?
ChallengeHow much carbon dioxide forms when 8 g of methane burns completely?
Error redoRusting is said to be only water on the surface with no change in mass. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	About one fifth, that is 21 percent	Most of the rest is nitrogen, about four fifths.
2	Put a glowing splint in and it relights	Oxygen supports burning but does not burn itself, so a glowing splint relighting identifies it.
3	A pop sound, and water is formed	Hydrogen combines with oxygen to give water, so droplets appear on the inside of the tube.
4	Iron combines with oxygen to form iron oxide, so the oxygen adds mass	The extra mass comes from oxygen in the air, not from the mass of water.
5	Salt water conducts electricity, which speeds up electron transfer and so the oxidation	That is why iron near the sea or touched by sweaty hands rusts so quickly.
6	The oxygen inside has been used up, and the rise is about one fifth of the air, which is the oxygen	The rise measures the volume of oxygen used and confirms that oxygen is about one fifth of air.
7	About 52.5 cm³	Oxygen is 21 percent of the air, and 250 times 21 divided by 100 gives 52.5.
8	A gain of 0.62 g, which is 12.4 percent	The gain is oxygen, and 0.62 divided by 5.00 times 100 gives the percentage.
9	22 g	Methane and carbon dioxide are in the mass ratio 16 to 44, so 8 g of methane gives 22 g.
10	Rusting is a chemical change in which oxygen is added, so the mass rises and iron oxide forms	If it were only water, drying would restore the mass, but rust cannot be wiped away.

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.

For combustion and oxidation questions ask three things: whether the question is about conditions, observations or mass, how many reactants and products there are, and which gas entering or leaving explains any change in mass.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.