Physical and Chemical Changes
28 Grade 8 Integrated Science questions on Physical and Chemical Changes, with worked marking schemes. 28 questions are available on this topic in full.
Question 1
1 markWhich of the following processes is reversible?
A. Freezing water into ice
B. Burning paper
C. Rusting of iron
D. Cooking an egg
(1 mark)
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5 marks(a) State two differences between a physical change and a chemical change. (2 marks)
(b) Classify each of the following as a physical or a chemical change:
(i) melting of ice; (ii) burning of paper; (iii) rusting of iron. (3 marks)
(5 marks)
Marking scheme
(a) Differences (any two): A physical change does not form a new substance while a chemical change forms a new substance; a physical change is usually easily reversible while a chemical change is usually difficult to reverse; in a physical change only the physical state or appearance changes while in a chemical change the chemical composition changes. (b) (i) melting of ice - physical change; (ii) burning of paper - chemical change; (iii) rusting of iron - chemical change.
Question 3
4 marksGive two differences between physical changes and chemical changes.
(4 marks)
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Create a free account to see itQuestion 4
5 marks(a) Distinguish between a physical change and a chemical change. (2 marks)
(b) Classify each of the following as a physical change or a chemical change:
(i) Melting of candle wax
(ii) Burning of a piece of paper
(iii) Rusting of an iron nail (3 marks)
(5 marks)
Marking scheme
(a) A physical change is a change in which no new substance is formed and the change can usually be reversed (only the physical state, shape or size changes), while a chemical change is a change in which one or more new substances are formed and it is usually not easily reversible. (b) (i) Melting of candle wax - physical change. (ii) Burning of a piece of paper - chemical change. (iii) Rusting of an iron nail - chemical change.
Question 5
1 markA learner leaves a cup of water outside on a hot day and later finds the cup empty. Which type of change has taken place?
A. A chemical change, because the water was destroyed
B. A chemical change, because a new substance was formed
C. A physical change, because a gas was produced by reaction
D. A physical change, because only the state of the water changed
(1 mark)
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1 markDissolving salt in water is a
A. physical change
B. permanent change
C. nuclear change
D. chemical change
(1 mark)
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1 markWhen a candle burns, the change that takes place is
A. both physical and chemical
B. only physical
C. only chemical
D. neither physical nor chemical
(1 mark)
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Create a free account to see itQuestion 8
1 markWhich of the following is a common indicator that a chemical reaction has taken place?
A. Production of a gas with bubbling
B. Ice cubes floating on water
C. Change in the size of a piece of chalk when broken
D. A liquid taking the shape of its container
(1 mark)
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Create a free account to see itQuestion 9
1 markWhich of the following is a chemical change?
A. Cutting paper
B. Dissolving sugar in water
C. Rusting of iron
D. Melting butter
(1 mark)
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Create a free account to see itQuestion 10
1 markA physical change can be identified because
A. a new substance is always formed
B. no new substance is formed
C. it always produces heat
D. it cannot be reversed
(1 mark)
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Create a free account to see itQuestion 11
1 markWhen milk is left in the open for two days it becomes sour and forms curds. This is a chemical change MAINLY because:
A. A new substance with a different taste and texture is formed
B. The milk can easily be returned to its fresh state
C. The milk simply changed its temperature
D. Only the colour of the milk changed
(1 mark)
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Create a free account to see itQuestion 12
4 marksA learner melted some candle wax and later burnt a candle.
(a) State whether melting of candle wax is a physical or chemical change, and give a reason. (2 marks)
(b) Give two observations that show that a chemical change took place when the candle was burning. (2 marks)
(4 marks)
Marking scheme
(a) Melting of candle wax is a physical change because no new substance is formed; the wax only changes from solid to liquid and can be turned back into solid wax on cooling (it is reversible). (b) Any two of: light/heat (energy) was given out; a new substance (carbon dioxide and water vapour / soot) was formed; the wax was used up and the change could not be reversed; a flame and smoke were produced.
Question 13
1 markWhich one of the following changes is EASILY reversible?
A. Freezing of water into ice
B. Burning of charcoal
C. Baking of dough into bread
D. Cooking of raw meat
(1 mark)
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Create a free account to see itQuestion 14
1 markWhich set contains ONLY physical changes?
A. Digesting food, dissolving salt, breaking glass
B. Rusting of iron, burning of wood, melting of ice
C. Souring of milk, boiling of water, cooking of an egg
D. Melting of butter, tearing of paper, freezing of water
(1 mark)
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Create a free account to see itQuestion 15
1 markA chemical change is characterised by all of the following EXCEPT
A. formation of a new substance
B. the substance retaining its original form
C. production of gas or heat
D. colour change
(1 mark)
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Create a free account to see itQuestion 16
1 markA nail left in the rain for several weeks turns reddish-brown and flaky. This change is BEST described as:
A. Condensation, a chemical change
B. Evaporation, a physical change
C. Rusting, a chemical change
D. Melting, a physical change
(1 mark)
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Create a free account to see itQuestion 17
1 markWhich of the following observations is the BEST evidence that a chemical change has occurred?
A. Formation of a new substance with different properties
B. Change in the shape of the material
C. Dissolving of sugar in water
D. Change from solid to liquid on heating
(1 mark)
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Create a free account to see itQuestion 18
4 marksA cook boils water and also fries an egg on the same jiko.
(a) Identify which activity is a physical change and which is a chemical change.
(b) Explain your answer for the frying of the egg.
(4 marks)
Marking scheme
(a) Boiling water - physical change (1); Frying an egg - chemical change (1). (b) Frying the egg is a chemical change because a new substance is formed - the egg changes permanently (the clear part becomes solid and white) and the change cannot be reversed back to a raw egg (2).
Question 19
4 marksClassify the following as physical or chemical changes:
(a) Boiling water
(b) Souring of milk
(c) Breaking a glass
(d) Digestion of food
(4 marks)
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Create a free account to see itQuestion 20
1 markA student burns a piece of paper and is left with ash. Why is burning classified as a chemical change?
A. The paper can easily be turned back into paper
B. No heat was involved in the process
C. The ash is a new substance and the change cannot be reversed
D. The paper only changed its shape
(1 mark)
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Create a free account to see itQuestion 21
4 marksA learner records four events during a science lesson: (i) an ice cube melting, (ii) a matchstick burning, (iii) sugar dissolving in tea, (iv) iron nails rusting. Classify each event as a physical or chemical change.
(4 marks)
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4 marksRusting of iron is a common problem in Kenyan homes and farms.
(a) State the two conditions necessary for iron to rust.
(b) Suggest two methods a farmer can use to prevent farm tools from rusting.
(4 marks)
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3 marksState three signs (indicators) that can be used to tell that a chemical change has taken place.
(3 marks)
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1 markBurning of wood is an example of a
A. temporary change
B. physical change
C. reversible change
D. chemical change
(1 mark)
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Create a free account to see itQuestion 25
5 marks(a) Distinguish between a physical change and a chemical change. (2 marks)
(b) Classify each of the following as a physical or a chemical change:
(i) melting of candle wax (ii) rusting of iron (iii) burning of paper. (3 marks)
(5 marks)
Marking scheme
(a) A physical change is a change in which no new substance is formed and is usually reversible (only the state, shape or size of the substance changes), while a chemical change is a change in which one or more new substances are formed and is usually not easily reversible. (2 marks) (b) (i) Melting of candle wax - physical change. (ii) Rusting of iron - chemical change. (iii) Burning of paper - chemical change. (1 mark each)
Question 26
3 marksDuring an experiment, a learner heated a blue copper(II) sulphate crystal (hydrated copper sulphate). It turned white and water droplets formed on the cooler parts of the test tube. When water was later added to the white solid, it turned blue again.
(a) State whether the heating of the blue crystals is a physical or chemical change, giving a reason. (2 marks)
(b) State one observation that shows the change can be reversed. (1 mark)
(3 marks)
Marking scheme
(a) It is a chemical change. Reason: heating drives off the water of crystallisation, which is chemically combined in the crystals, forming a new substance (white anhydrous copper(II) sulphate) that is different from the blue hydrated copper(II) sulphate. (It is, however, a reversible chemical change.) (b) When water is added to the white anhydrous solid, it turns blue again, returning to the original blue colour/substance (the hydrated copper(II) sulphate is reformed).
Question 27
1 markMelting of ice is an example of a
A. biological change
B. chemical change
C. nuclear change
D. physical change
(1 mark)
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6 marks(a) State two differences between a physical change and a chemical change.
(b) Give one example of each type of change from everyday life in your home.
(6 marks)
Marking scheme
(a) Two differences (2 marks each = 4): Physical change - no new substance formed / usually reversible / only physical properties such as state, shape or size change; Chemical change - a new substance is formed / usually irreversible / new properties, may involve energy change, colour change, gas or precipitate. (b) One example of a physical change e.g. melting ice, dissolving salt (1); one example of a chemical change e.g. cooking food, burning charcoal, rusting (1).
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