Retrieval practice

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    Created by
    Shekinah Obare

    Cards (89)

    • In everyday language what is a "pure" substance?
      A substance that has had nothing added to it and is in its natural state.
    • Give an example of a "pure" substance that matches the everyday definition of pure.

      Pure milk.
    • In chemistry, what is a pure substance?
      A single element or compound, not mixed with any other substance.
    • Why is 100% pure orange juice not a chemically pure substance?
      It is a mixture of elements and compounds
    • How can pure substances be distinguished from impure ones?
      By measuring their melting/boiling points and comparing to known values.
    • Describe the melting and boiling points of pure substances.
      One specific temperature.
    • Describe the melting points of an impure substance. 

      Lower than the pure substance and has a range.
    • Describe the boiling point of an impure substance.
      Higher than the pure substance and has a range
    • What is a formulation?
      A useful product that is a complex mixture where each chemical in the mixture has a specific purpose and is present in precisely measured amounts.
    • How are formulations made?
      Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
    • Name 6 formulations.
      Fuels, cleaning agents, paints, medicines, alloys, fertilisers and processed foods.
    • How can you spot a formulation in an exam question?
      Because a table of ingredients with specific measured amounts of each is given.
    • What is chromatography?
      Separation of mixtures to identify their components.
    • Chromatography involves interactions between two phases, name them.
      Stationary phase and mobile phase.
    • In paper chromatography (TLC) what is the stationary phase?
      The chromatography paper
    • In paper chromatography (TLC) what is the mobile phase?
      The solvent.
    • Describe how chromatography works.
      The solvent moves through the paper. Different compounds have different solubilities in the solvent and different attractions to the paper. Different compounds are carried different distances.
    • What is the equation for calculating Rf?
      Rf = distance moved by solvent / distance moved by spot
    • What does a substance's Rf value depend on?
      How soluble it is in the solvent.
    • How is distance to solvent front measured?
      From the base line to the solvent front.
    • How is distance to spot measured?
      From the base line to the centre of the spot.
    • How can chromatography tell you the identity of a compound?
      Different compounds have different Rf values in different solvents.
    • How can chromatography test purity of a compound?
      A pure compound produces one spot in any solvent but mixtures separate into different spots depending on the solvent.
    • When running a chromatography, why must the base line be drawn in pencil?
      Because ink would run up the chromatography paper.
    • When running a chromatography, why must the compounds be soluble in the solvent?
      So the compounds can move up the paper and separate.
    • Why is a lid used in chromatography?
      To prevent the solvent evaporating away.
    • Why must the solvent level be below the base line in chromatography?
      To prevent the compounds dissolving into the solvent instead of moving up the paper.
    • Describe the test for hydrogen gas.
      Ignite the gas with a lit splint.
    • Describe the observation for the hydrogen gas test.
      A squeaky pop.
    • Describe the test for oxygen gas.
      Place a glowing splint into the gas.
    • Describe the observation for the oxygen gas test.
      The glowing splint relights.
    • Describe the test for carbon dioxide gas.
      Bubble the gas through limewater.
    • Describe the observation for the carbon dioxide gas test.
      Limewater turns cloudy.
    • What is the chemical name for limewater?
      Calcium hydroxide.
    • Describe the test for chlorine gas.
      Add damp litmus paper to the gas.
    • Describe the observation for the chlorine gas test.
      Damp litmus turns white in colour
    • Name two tests for positive ions.
      Flame test and NaOH test.
    • Describe the steps needed to carry out a flame test.
      Clean a nichrome wire loop in acid and hold in a blue Bunsen flame. Dip the wire into the compound and place back in the flame. Record the colour observed.
    • Which 5 ions are identified using a flame test?
      Li+, Na+, K+, Ca2+, Cu2
    • Which ion produces a crimson flame?
      Li+
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