Chapter 3 Practice Paper: Chemical Changes — mark scheme (print)

QuizQuipPractice Series

QQ/S2SCI/CH3

Secondary 2 · Lower Secondary Science (G2 / G3)

Mark scheme

Chemical Changes

Chapter 3 Practice Paper · Maximum mark: 30

Notes for markers

Award one mark for each point marked [1], up to the marks shown for the part.
Accept answers worded differently that show the same understanding.
Units are required where the answer line shows one. ecf: allow an error carried forward.

Section A: Multiple-choice questions[10 marks]

Question	Answer
1	ARust is a new substance, so the change is chemical.	1
2	CThe product is the substance named on the right of the arrow.	1
3	BHydrogen gives a pop with a lighted splint.	1
4	DNeutralisation: acid + alkali → salt + water.	1
5	AAcid turns blue litmus red. Alkali turns red litmus blue.	1
6	CCarbon dioxide turns limewater milky. A pop is hydrogen. A glowing splint relights in oxygen.	1
7	DThermal decomposition is breaking a compound down by heat.	1
8	BNo atoms enter or leave. They are rearranged, so the total mass stays the same.	1
9	ARusting is slow oxidation. Iron gains oxygen. Water is also needed.	1
10	CGreen means neutral. Strong acid is red. Strong alkali is purple.	1

Section B: Structured questions[20 marks]

Question	Answer and marking points	Marks
1(a)	Hydrogen [1]	1
1(b)	magnesium + hydrochloric acid → magnesium chloride + hydrogen Reactants named: magnesium and hydrochloric acid [1] Products named: magnesium chloride and hydrogen [1]	2
1(c)	Glowing splint relights [1]	1
1(d)	The gas turns limewater milky. Limewater turns milky [1]	1
	Total for Question 1	5
2(a)	hydrochloric acid + sodium hydroxide → sodium chloride + water Acid and alkali named [1] Salt and water named [1]	2
2(b)	Red, orange or yellow [1]	1
2(c)	Green [1]	1
2(d)	Neutralisation [1]	1
	Total for Question 2	5
3(a)	The atoms are rearranged into magnesium oxide. No atoms enter or leave the flask, so the total mass stays the same. Atoms are rearranged / a new substance forms [1] Nothing enters or leaves, so mass is conserved [1]	2
3(b)	Oxygen from the air joins with the magnesium. That oxygen was not in the beaker at the start, so the solid product has more mass. Oxygen from the air is added [1] The extra mass is the oxygen that combined [1]	2
3(c)	The atoms leave with the gas. They are not destroyed. The atoms leave with the gas / they are not destroyed [1]	1
	Total for Question 3	5
4(a)	Oxygen and water. Oxygen / air [1] Water [1]	2
4(b)	It keeps oxygen and water away from the iron. It is a barrier to oxygen and water [1]	1
4(c)	fuel + oxygen → carbon dioxide + water Fuel and oxygen as reactants [1] Carbon dioxide and water as products [1]	2
	Total for Question 4	5

— End of mark scheme —