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Year 9 Science — Mixtures, concentration and separation

Tell solutions, suspensions and colloids apart, work out a concentration as a percentage, and choose the right method for pulling a given mixture apart.

Name: ________________________

Before you start

Three beakers, and what the laser beam does in each of them.

123
  1. 1. Salt in water — the beam crosses unseen
  2. 2. Chalk powder in water — the beam shows, and the powder settles
  3. 3. Milk in water — the beam shows, and nothing settles

Shine the light in from the side and watch from a right angle. The path you can see is light being scattered off particles big enough to scatter it.

  1. 1.Match each separation method to the mixture it is meant for.

    • Distillation
    • Separating funnel
    • Sublimation
    • Paper chromatography
    • Centrifugation
    • A solid that sublimes mixed with one that does not
    • The coloured components of an ink or a dye
    • Two immiscible liquids
    • Two miscible liquids with different boiling points
    • Heavier particles from a lighter liquid

  2. 2.25 mL of juice concentrate is made up with water to 250 mL of drink. What is the volume by volume percentage of concentrate? Answer with a number.

  3. 3.A black ink spot is put on a paper strip and the strip is dipped so the water level starts below the spot. The water rises and the spot spreads into several coloured bands. Why do the bands separate?

    • a) The heavier colours sink while the lighter ones rise
    • b) The components travel up the paper at different speeds
    • c) Water dissolves some colours and destroys the others
    • d) The paper reacts with each colour to make a new one

  4. 4.8 g of glucose is dissolved in water and made up to 200 mL of solution. What is the mass by volume percentage? Answer with a number.

  5. 5.A saturated solution of a solid is made at 60 °C and then cooled slowly to 40 °C. What happens?

    • a) Some of the solid separates out, because less of it can stay dissolved at the lower temperature
    • b) Nothing changes, because solubility does not depend on temperature
    • c) More of the solid dissolves, because cooling makes room for it
    • d) The solvent boils away and leaves the solid behind

  6. 6.20 g of sugar is dissolved in 80 g of water. What is the mass by mass percentage of the solution? Answer with a number.

  7. 7.A mixture of crushed camphor and sand is heated gently under an inverted funnel, and a white solid appears on the inside of the funnel. What has happened?

    • a) The camphor turned straight to vapour and then back to solid, while the sand stayed put
    • b) The two solids reacted to make a new white compound
    • c) The camphor melted, boiled and then condensed as a liquid
    • d) The sand melted and rose as a vapour, leaving the camphor behind

  8. 8.Put the steps of growing copper sulfate crystals in order, starting from Warm the water with the solid, stirring, until no more will dissolve.

    • Filter off the crystals and rinse them with cold water
    • Filter the hot saturated solution to take out insoluble impurities
    • Cover the filtrate and leave it to cool slowly, undisturbed
    • Leave the crystals to dry on a watch glass
    • Warm the water with the solid, stirring, until no more will dissolve

Answer key — Year 9 Science — Mixtures, concentration and separation

  1. 1. Distillation → Two miscible liquids with different boiling points; Separating funnel → Two immiscible liquids; Sublimation → A solid that sublimes mixed with one that does not; Paper chromatography → The coloured components of an ink or a dye; Centrifugation → Heavier particles from a lighter liquid
  2. 2. 10
  3. 3. b) The components travel up the paper at different speeds
  4. 4. 4
  5. 5. a) Some of the solid separates out, because less of it can stay dissolved at the lower temperature
  6. 6. 20
  7. 7. a) The camphor turned straight to vapour and then back to solid, while the sand stayed put
  8. 8. 1. Warm the water with the solid, stirring, until no more will dissolve 2. Filter the hot saturated solution to take out insoluble impurities 3. Cover the filtrate and leave it to cool slowly, undisturbed 4. Filter off the crystals and rinse them with cold water 5. Leave the crystals to dry on a watch glass