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Year 8 Science — Elements, compounds and mixtures

Tell an element from a compound from a mixture, and say which of them can be taken apart by physical means.

Name: ________________________

  1. 1.Could you separate the hydrogen and oxygen in water by a physical method such as filtering, evaporating or using a magnet?

    • a) Yes — a strong enough magnet pulls the hydrogen out
    • b) No — the elements in a compound are held too tightly for any physical method
    • c) Yes — evaporating the water leaves the oxygen behind
    • d) No — because water contains just one element to begin with

  2. 2.Elements divide into two families. Sort these into theirs.

    Groups: Metal · Non-metal

    • Iron
    • Aluminium
    • Oxygen
    • Carbon
    • Sulfur
    • Gold

  3. 3.Silicon and boron sit awkwardly between the two families of elements. What are such elements called?

    • a) Compounds
    • b) Alloys
    • c) Metalloids
    • d) Minerals

  4. 4.In water, what is the ratio of the number of hydrogen atoms to the number of oxygen atoms? Write it as a ratio.

  5. 5.A packet of ghee is labelled 'pure'. A scientist looks at it and calls it impure. Why the disagreement?

    • a) In science, pure means safe to eat, and the ghee is not
    • b) The scientist thinks the ghee has had something cheaper added to it
    • c) In science, pure means made of a single substance, while in everyday use it means unadulterated
    • d) In science, any substance sold in a packet counts as impure

  6. 6.Sort these substances into the three kinds the chapter names.

    Groups: Element · Compound · Mixture

    • Sulfur
    • Water
    • Brass
    • Air
    • Gold
    • Sodium chloride

  7. 7.Sugar heated in a boiling tube turns brown, then black, and droplets of water appear near the open end. What does that show about sugar?

    • a) It is an element, since carbon is left behind
    • b) It is a mixture of carbon and water stirred together
    • c) It is a metal, since it darkens on heating
    • d) It is a compound, made of carbon, hydrogen and oxygen

  8. 8.A pure substance is one of two things. Which pair is it?

    • a) A compound or a mixture
    • b) A metal or a non-metal
    • c) An element or a mixture
    • d) An element or a compound

Answer key — Year 8 Science — Elements, compounds and mixtures

  1. 1. b) No — the elements in a compound are held too tightly for any physical method
  2. 2. Iron → Metal; Aluminium → Metal; Gold → Metal; Carbon → Non-metal; Sulfur → Non-metal; Oxygen → Non-metal
  3. 3. c) Metalloids
  4. 4. 2:1
  5. 5. c) In science, pure means made of a single substance, while in everyday use it means unadulterated
  6. 6. Gold → Element; Sulfur → Element; Water → Compound; Sodium chloride → Compound; Air → Mixture; Brass → Mixture
  7. 7. d) It is a compound, made of carbon, hydrogen and oxygen
  8. 8. d) An element or a compound