Elements and Compounds

27 Grade 8 Integrated Science questions on Elements and Compounds, with worked marking schemes. 27 questions are available on this topic in full.

1. Question 1

   1 mark

   A learner in Nakuru examines a sample of table salt (sodium chloride) and a sample of pure copper wire. Which statement correctly classifies these two substances?

   A. Table salt is a compound while copper is an element

   B. Both table salt and copper are compounds

   C. Table salt is an element while copper is a compound

   D. Both table salt and copper are elements

   (1 mark)

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2. Question 2

   4 marks

   Differentiate between an element and a compound. Give one example of each.

   (4 marks)

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3. Question 3

   1 mark

   Elements are classified as metals and non-metals. Which of the following is a non-metal?

   A. Sulphur

   B. Copper

   C. Iron

   D. Aluminium

   (1 mark)

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4. Question 4

   4 marks

   Distinguish between an element and a compound, giving one example of each found in everyday life in Kenya.

   (4 marks)

   Marking scheme

   An element is a pure substance made of only one type of atom and cannot be broken down into simpler substances by chemical means (1 mark); example - copper/gold/oxygen (1 mark). A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio (1 mark); example - water/table salt/carbon dioxide (1 mark).

5. Question 5

   1 mark

   The chemical symbol for iron is:

   A. Ir

   B. Fe

   C. In

   D. Fr

   (1 mark)

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6. Question 6

   4 marks

   (a) State the difference between an element and a compound. (2 marks)

   (b) Common salt (sodium chloride) is formed when sodium reacts with chlorine. State whether sodium chloride is an element or a compound, and give a reason. (2 marks)

   (4 marks)

   Marking scheme

   (a) An element is a pure substance made up of only one type of atom and cannot be broken down into simpler substances by chemical means, while a compound is a pure substance formed when two or more different elements are chemically combined in a fixed ratio and can be broken down into its constituent elements by chemical means. (b) Sodium chloride is a compound. Reason: it is formed by the chemical combination of two different elements (sodium and chlorine) in a fixed ratio, and its properties differ from those of the elements that make it.

7. Question 7

   4 marks

   A learner is given samples of magnesium, oxygen and magnesium oxide.

   (a) State whether each of the following is an element or a compound:

   (i) magnesium (ii) magnesium oxide. (2 marks)

   (b) Explain one difference between an element and a compound. (2 marks)

   (4 marks)

   Marking scheme

   (a) (i) Magnesium is an element. (ii) Magnesium oxide is a compound. (1 mark each) (b) An element is made up of only one kind of atom and cannot be broken down into simpler substances by chemical means, whereas a compound is formed when two or more different elements combine chemically in a fixed ratio and can be broken down into its constituent elements by chemical means. (2 marks)

8. Question 8

   1 mark

   Which of the following is a compound?

   A. Iron

   B. Gold

   C. Oxygen

   D. Water

   (1 mark)

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9. Question 9

   1 mark

   During an experiment, a colourless gas relights a glowing splint. This element is most likely:

   A. Nitrogen

   B. Carbon dioxide

   C. Oxygen

   D. Hydrogen

   (1 mark)

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10. Question 10

    1 mark

    Metals are generally good conductors of

    A. magnetism only

    B. heat and electricity

    C. sound only

    D. light only

    (1 mark)

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11. Question 11

    1 mark

    A compound differs from a mixture because a compound

    A. can be separated by physical methods

    B. retains the properties of its components

    C. has its components chemically combined in fixed proportions

    D. can have varying composition

    (1 mark)

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12. Question 12

    4 marks

    (a) State the difference between an element and a compound. (2 marks)

    (b) Water is a compound made up of two elements. Name the two elements. (2 marks)

    (4 marks)

    Marking scheme

    (a) An element is a pure substance made up of only one type of atom and cannot be broken down into simpler substances by chemical means, while a compound is a pure substance formed when two or more different elements combine chemically in a fixed ratio and can be broken down into its elements by chemical means. (b) The two elements in water are hydrogen and oxygen.

13. Question 13

    1 mark

    The chemical formula of carbon dioxide is CO₂. This means it contains

    A. one carbon atom and one oxygen atom

    B. one carbon atom and two oxygen atoms

    C. two carbon atoms and two oxygen atoms

    D. two carbon atoms and one oxygen atom

    (1 mark)

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14. Question 14

    1 mark

    A student is given water, oxygen gas, carbon dioxide and gold. Which of these is an element?

    A. Gold

    B. Water

    C. Both water and carbon dioxide

    D. Carbon dioxide

    (1 mark)

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15. Question 15

    3 marks

    State three properties of metals.

    (3 marks)

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16. Question 16

    4 marks

    A Grade 8 class was given three substances: pure copper, oxygen gas and water.

    (a) Classify each substance as an element or a compound. (3 marks)

    (b) State one reason why water is classified as a compound. (1 mark)

    (4 marks)

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17. Question 17

    1 mark

    Which of the following symbols correctly represents the element sodium?

    A. N

    B. S

    C. So

    D. Na

    (1 mark)

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18. Question 18

    1 mark

    When magnesium ribbon is burned in air during a laboratory activity, it forms a white powder. The white powder produced is best described as:

    A. An element (oxygen)

    B. A compound (magnesium oxide)

    C. A mixture of magnesium and oxygen

    D. An element (magnesium)

    (1 mark)

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19. Question 19

    4 marks

    Common salt (sodium chloride) is a compound used in most Kenyan homes.

    (a) Name the two elements that combine to form common salt. (2 marks)

    (b) Explain why the properties of common salt differ from the properties of the elements that form it. (2 marks)

    (4 marks)

    Marking scheme

    (a) Sodium and chlorine (2 marks, 1 each). (b) When elements combine chemically to form a compound, they lose their individual properties and the new compound has entirely new properties (1 mark); e.g. sodium is a reactive metal and chlorine is a poisonous gas, but the salt formed is a safe, edible solid (1 mark).

20. Question 20

    1 mark

    Which of the following is a characteristic that distinguishes a compound from a mixture?

    A. A compound can be separated by physical means such as filtration

    B. A compound retains the individual properties of its components

    C. A compound can be formed by simply mixing substances together

    D. A compound has a fixed ratio of its combining elements

    (1 mark)

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21. Question 21

    1 mark

    The smallest particle of an element that still retains the properties of that element is called:

    A. An atom

    B. A compound

    C. A molecule of a compound

    D. A mixture

    (1 mark)

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22. Question 22

    1 mark

    An element is a substance that

    A. is made up of two or more elements

    B. cannot be broken down into simpler substances by chemical means

    C. is always a liquid

    D. can be separated by filtration

    (1 mark)

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23. Question 23

    1 mark

    The chemical symbol for sodium is

    A. Na

    B. Sd

    C. So

    D. No

    (1 mark)

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24. Question 24

    6 marks

    State three differences between a compound and a mixture.

    (6 marks)

    Marking scheme

    Any three differences, 2 marks each (1 for the compound side, 1 for the mixture side): Compound formed by chemical combination / mixture formed by physical mixing; Compound has elements in a fixed ratio / mixture in any ratio; Compound cannot be separated by physical means / mixture can be separated physically; Compound has properties different from its components / mixture retains component properties.

25. Question 25

    4 marks

    (a) State the difference between an element and a compound. (2 marks)

    (b) Water is a compound made up of hydrogen and oxygen. Give two reasons why water is classified as a compound and not a mixture. (2 marks)

    (4 marks)

    Marking scheme

    (a) An element is a pure substance made up of only one type of atom and cannot be broken down into simpler substances by chemical means, while a compound is a pure substance formed when two or more different elements combine chemically in a fixed ratio. (b) (i) The hydrogen and oxygen in water are chemically combined (joined by chemical bonds), not just physically mixed. (ii) The hydrogen and oxygen are combined in a fixed ratio (2:1) and cannot be separated by physical means such as filtering; the properties of water are completely different from those of hydrogen and oxygen.

26. Question 26

    1 mark

    Which of the following is an element?

    A. Water

    B. Carbon dioxide

    C. Salt

    D. Copper

    (1 mark)

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27. Question 27

    1 mark

    Which pair below consists ONLY of elements?

    A. Water and salt

    B. Oxygen and sugar

    C. Carbon dioxide and hydrogen

    D. Hydrogen and oxygen

    (1 mark)

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