1. 1:1
2. 1:2
3. 2:1
4. 4:1

1. In CuO + H₂ → Cu + H₂O, the reducing agent is: (1)

1. CuO
2. H₂
3. Cu
4. H₂O

1. Nitrogen flushing delays rancidity because it: (1)

1. increases the packet temperature
2. adds water to the food
3. limits contact between fats and oxygen
4. converts fats into proteins

For Questions 7-9 choose:

1. Both A and R are true, and R correctly explains A.
2. Both A and R are true, but R does not correctly explain A.
3. A is true, but R is false.
4. A is false, but R is true.

1. Assertion: A balanced equation obeys conservation of mass. Reason: The number of atoms of each element is equal on both sides. (1)

1. Assertion: Silver chloride turns grey in sunlight. Reason: Silver chloride combines with chlorine to form a grey compound. (1)

1. Assertion: CaO + H₂O → Ca(OH)₂ is a combination reaction. Reason: Two reactants form one product. (1)

Section B - Very short answers - 6 marks

1. Why must a magnesium ribbon be cleaned before burning? Write the balanced equation for its burning. (2)

1. State two differences between displacement and double displacement reactions. (2)

1. Why is respiration exothermic? Write the equation used in this chapter. (2)

Section C - Short answers - 6 marks

1. Green ferrous sulphate crystals are heated strongly. State two observations, name the reaction type and write the balanced decomposition equation. (3)

1. A student mixes lead nitrate and potassium iodide solutions. Write the observation and balanced equation. Explain why the reaction has two valid classifications. (3)

Section D - Long answer - 5 marks

1. Compare thermal, electrolytic and photochemical decomposition. For each, name the energy supplied and write one balanced equation. Finish by explaining why all three are decomposition reactions. (5)

Section E - Case-based question - 4 marks

1. Three unlabeled stations show the following results:

• Station P becomes warm when water is added to a white solid.
• Station Q changes from a blue solution to a pale-green solution when an iron nail is added.
• Station R contains an oily food sample that develops an unpleasant smell after long exposure to air.

(a) Name the white solid at Station P. (1)

(b) Classify the reaction at Station P. (1)

(c) Write the balanced equation for Station Q. (1)

(d) Name the process at Station R and state one way to slow it. (1)

1. Respiration releases energy when glucose reacts with oxygen, so it is exothermic. C₆H₁₂O₆(aq) + 6O₂(aq) → 6CO₂(aq) + 6H₂O(l) + Energy. Award one point for the explanation and one for the equation.

Section C

1. Any two source observations: green crystals first lose water/change colour; a brown solid forms; gases with the smell of burning sulphur are released. It is thermal decomposition. 2FeSO₄(s) →[Heat] Fe₂O₃(s) + SO₂(g) + SO₃(g). Award one point for two observations, one for type and one for the equation.

1. A yellow PbI₂ precipitate forms. Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq). It is double displacement because ions exchange partners, and precipitation because an insoluble solid forms. Award one point each for observation, equation and both linked classifications.

Section D

1. Award the five points below:

1. Thermal decomposition uses heat: CaCO₃(s) →[Heat] CaO(s) + CO₂(g).
2. Electrolytic decomposition uses electricity: 2H₂O(l) →[Electricity] 2H₂(g) + O₂(g).
3. Photochemical decomposition uses light: 2AgCl(s) →[Sunlight] 2Ag(s) + Cl₂(g).
4. The equations are balanced and show the conditions clearly.
5. In every case, one reactant breaks into two or more products.

Section E

• (a) Calcium oxide or quicklime, CaO.
• (b) Combination and exothermic.
• (c) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s).
• (d) Rancidity. Accept antioxidants, an airtight container or nitrogen flushing.