Six-mark questions

Six-mark questions are extended open response questions. These require longer answers than the structured questions. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.

To gain full marks, you need to:

  • support explanations using scientific knowledge and understanding
  • use appropriate scientific words and terms
  • write clearly and link ideas in a logical way
  • maintain a sustained line of reasoning, rather than getting lost or bogged down

Six-mark questions often use these command words:

  • Describe - you need to give an account but no reason
  • Explain - you must give reasons or explanations
  • Devise - you must plan or invent a procedure using your scientific knowledge and understanding
  • Evaluate - you must review information, including identifying strengths and weaknesses, and make a supported conclusion

Six-mark questions may be synoptic questions. These questions bring together ideas from two or more topics. For example, a question about fertilisers could include ideas about covalent substances, acids and alkalis, chemical calculations, and effects on the environment.

The answers shown here give marking points as bullet points. You do not usually need to include all of them to gain six marks, but you do need to write in full sentences, linking them logically and clearly.

Edexcel questions courtesy of Pearson Education Ltd.

Sample question 1 - Foundation

Question

Describe the experimental procedure to carry out a titration to find the exact volume of sulfuric acid needed to neutralise 25.0 cm3 of sodium hydroxide solution and obtain pure, dry crystals of sodium sulfate. [6 marks]

Your answer should include the following:

  • Rinse the pipette with alkali and the burette with acid.
  • Measure alkali using a pipette into suitable container, eg flask/beaker and place flask on a white tile.
  • Add a few drops of indicator/suitable named indicator, eg methyl orange/phenolphthalein.
  • Fill the burette with acid and read volume of acid in the burette.
  • Add acid from the burette to the flask slowly, swirling the flask until indicator just changes colour.
  • Read the volume of acid in the burette at the end of titration.
  • Repeat experiment until you get concordant results.
  • Mix the same volume of alkali with the volume of acid determined from the titration but do not add indicator.
  • Pour neutralised solution into an evaporating basin then heat solution/leave the water to evaporate until pure salt crystals are left.
  • Dry crystals using absorbent paper/warm oven.

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Sample question 2 - Higher

Question

Barium sulfate is prepared by reacting barium chloride with sodium sulfate. The barium sulfate is formed as a precipitate.

Describe an experiment to prepare a pure, dry sample of barium sulfate, starting with barium chloride crystals and sodium sulfate crystals. [6 marks]

Your answer should include the following:

Reactants:

  • dissolve reactants barium chloride and sodium sulfate (in water)
  • mix reactants/solutions together
  • a precipitate of barium sulfate forms
  • stir to mix
  • use of appropriate apparatus beakers, flasks, stirring rods

Separating the product:

  • filter the mixture
  • use of filter funnel and paper

Making pure dry salt:

  • solid/precipitate of barium sulfate stays in filter paper
  • wash solid/precipitate with water
  • dry in oven/leave to dry/in a warm place

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Sample question 3 - Foundation

Question

Soluble salts of metals can be made by reacting one of the metal’s insoluble compounds with the appropriate acid.

Describe a plan for an experiment to prepare pure, dry crystals of magnesium sulfate, MgSO4, by reacting a suitable insoluble magnesium compound with a suitable acid.

You may include equations in your description if you wish. [6 marks]

Your answer should include the following:

  • Suitable acid: sulfuric acid.
  • Suitable substance: magnesium oxide/magnesium carbonate/magnesium hydroxide/magnesium.
  • Equation for reaction:
    • MgO + H2SO4 → MgSO4 + H2O
    • or Mg[OH]2 + H2SO4 → MgSO4 + 2H2O
    • or MgCO3 + H2SO4 → MgSO4 + H2O + CO2
    • or Mg + H2SO4 → MgSO4 + H2
  • Warm acid solution.
  • Add solid reactant to acid until in excess solid remains (oxide and hydroxide)/add solid a little at a time until there are no more bubbles (carbonate and metal).
  • Filter off the excess solid, pour remaining solution into an evaporating basin.
  • Heat the solution/leave the water to evaporate until pure salt crystals form and then dry salt crystals with absorbent paper/leave to dry.

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Sample question 4 - Higher

Question

Electrolysis of acidified water can produce hydrogen and oxygen.

The apparatus available for the electrolysis is:

  • water containing some dilute sulfuric acid
  • two carbon rods
  • a suitable container for the electrolysis reaction
  • a suitable source of electricity
  • test tubes

Describe how the apparatus can be set up to electrolyse the acidified water, and collect the gases produced. Include a description and the results of the test that could be carried out to identify where each gas is formed.

You may use a diagram to help your answer. [6 marks]

Your answer should include the following:

Experiment set up:

  • acidified water in container
  • carbon rods under surface of water/acid
  • carbon rods attached to electrical supply
  • dc supply used
  • electrodes identified as positive and negative
  • test tubes filled with water/acid upside down over electrodes to collect gases.

About the gases:

  • hydrogen formed at negative electrode
  • hydrogen formed at negative electrode
  • test with lighted splint
  • squeaky pop (with air)/burns
  • oxygen formed at positive electrode
  • test with glowing splint
  • splint relights
  • twice as much hydrogen as oxygen produced

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