Science 8 · Unit 2: Properties of materials · Cambridge Lower Secondary Science Stage 8

Questions

1. 1. What is paper chromatography used for?

   • measuring temperature
   • separating a mixture of soluble substances like dyes
   • making solutions stronger
   • separating sand from water
   Check

2. 2. Why is the spot placed above the solvent level?

   • to make it dry faster
   • it doesn't matter
   • so it doesn't dissolve straight into the solvent in the beaker
   • so the paper is heavier
   Check

3. 3. Why is the start line drawn in pencil, not ink?

   • Ink is too expensive.
   • Pencil doesn't dissolve and separate.
   • Pencil is darker.
   • Pencil makes the solvent move faster.
   Check

4. 4. How does chromatography separate substances?

   • Substances travel different distances as the solvent moves up the paper.
   • They are boiled away.
   • Magnets pull them apart.
   • Heavy substances sink.
   Check

5. 5. A substance gives only one spot. What does this show?

   • It is a pure substance.
   • It is insoluble.
   • It is a solvent.
   • It is a mixture.
   Check

6. 6. The petal liquid gives three spots. Is it pure or a mixture?

   • pure
   • a mixture
   Check

7. 7. What is the picture of the separated spots called?

   • a graph only
   • a thermometer
   • a filtrate
   • a chromatogram
   Check

8. 8. How can the scientist tell if a drink contains a banned colouring?

   • the drink tastes odd
   • a spot doesn't match any permitted colouring
   • the water turns cold
   • the spot is very large
   Check

9. 9. Why should the scientist do further tests on an unmatched dye?

   • It is water.
   • It is definitely safe.
   • The paper is broken.
   • It might be a banned or harmful chemical.
   Check

10. 10. Sofia's petal spot didn't move with water as the solvent. Why?

    • The water was too cold.
    • The paper was too long.
    • The spot was too dry.
    • The substances are insoluble in water.
    Check

11. 11. What should Sofia try next?

    • a pen line
    • a different solvent, such as ethanol
    • a bigger spot
    • more water
    Check

12. 12. Why did Sofia let each drop dry before adding another?

    • to make the paper heavier
    • to change the colour
    • to keep the spot small and concentrated
    • to stop the solvent moving
    Check

13. 13. What is the solvent front?

    • the bottom of the beaker
    • how far the solvent has travelled up the paper
    • the darkest spot
    • the start line
    Check

14. 14. Two spots at the same height in different samples suggest what?

    • Both are insoluble.
    • They may be the same substance.
    • They are definitely different.
    • Neither has a solvent.
    Check

15. 15. Black ink separates on chromatography paper. Which coloured ink is carried furthest up the paper?

    • the most soluble one
    • the one with the biggest spot
    • the least soluble one
    • the darkest one
    Check

16. 16. Why is ethanol used instead of water to make a chromatogram of the green pigment in spinach?

    • Ethanol moves more slowly.
    • The green pigment doesn't dissolve in water.
    • Water would turn the pigment red.
    • Ethanol is cheaper than water.
    Check

17. 17. Why is the paper taken out before the solvent reaches the top?

    • so the solvent evaporates faster
    • so the paper doesn't get dry
    • so the spots don't run off the end
    • so the pencil line dissolves
    Check