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

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

  2. 2.Sort each description by the kind of mixture it belongs to.

    Groups: Solution · Colloid · Suspension

    • Particles smaller than 1 nanometre
    • Particles you can see, which settle when left alone
    • Scatters a light beam and yet stays evenly spread
    • Lets a laser beam through with no visible path
    • Particles larger than 1000 nanometres
    • Particles between 1 and 1000 nanometres

  3. 3.Mustard oil and water have settled into two layers in this separating funnel. Tap the layer that comes out of the stopcock first.

    Write the number of the part.

    123

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

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

  5. 5.8 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.

  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.Brass is described as a homogeneous mixture of about 80 per cent copper and 20 per cent zinc. What is such a mixture called, and can it be separated physically?

    • a) A suspension, and filtration will separate it
    • b) A compound, and no method of any kind will separate it
    • c) An alloy, and physical methods cannot separate its components
    • d) A colloid, and centrifugation will separate it

  8. 8.A talcum powder is 4 per cent zinc oxide by mass. How much zinc oxide is there in 300 g of the powder, in g? Answer with a number.

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

  1. 1. 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
  2. 2. Particles smaller than 1 nanometre → Solution; Lets a laser beam through with no visible path → Solution; Particles between 1 and 1000 nanometres → Colloid; Scatters a light beam and yet stays evenly spread → Colloid; Particles larger than 1000 nanometres → Suspension; Particles you can see, which settle when left alone → Suspension
  3. 3. 2 — The lower layer
  4. 4. 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
  5. 5. 4
  6. 6. 20
  7. 7. c) An alloy, and physical methods cannot separate its components
  8. 8. 12