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

Marble chips react with dilute hydrochloric acid to produce carbon dioxide gas.

The rate of this reaction can be changed by changing the size of the marble chips.

Describe how you could investigate what effect using smaller marble chips has on the rate of this reaction. Predict and explain the effect of using smaller marble chips on the reaction rate. [6 marks]

Your answer should include the following:

  • measure volume of acid/stated volume
  • measure mass of marble chips/stated mass
  • add acid to marble or marble to acid in a suitable container, eg flask, beaker, boiling tube, test tube
  • collect the gas in a gas syringe/measuring cylinder over water or bubble gas through limewater/bubble gas through water
  • measure the amount/volume of carbon dioxide or count the bubbles/fixed volume of carbon dioxide
  • measure mass/mass loss (on a balance)
  • time/measure how long the reaction takes
  • repeat experiment with different size marble chips
  • use the same mass of marble chips
  • use the same volume/concentration/mass of acid/same acid
  • crush the marble/use powdered marble

Results:

  • smaller chips (of marble) have a more vigorous
  • reaction/produce more fizzing/bubbles
  • smaller chips take less time to react/produce a certain volume of gas/have a certain mass loss
  • smaller chips have a larger surface area
  • smaller chips react faster
  • larger surface gives a faster reaction

[6]

Sample question 2 - Foundation

Question

Hydrochloric acid reacts with magnesium metal to produce hydrogen gas:

Magnesium + hydrochloric acid → magnesium chloride + hydrogen

Describe how you could use magnesium ribbon, and a solution of hydrochloric acid, to show that decreasing the concentration of the hydrochloric acid changes the rate of this reaction. [6 marks]

Your answer should include the following:

Method:

  • dilute the acid...
  • to make different concentrations
  • add magnesium to acid...
  • in suitable container
  • equal volumes of the acids
  • equal lengths of magnesium

Observations:

  • observe/count bubbles
  • highest concentration magnesium reacts, lowest concentration magnesium does not react
  • time how long it takes for the magnesium to disappear
  • measure volume gas produced
  • measure decrease in mass

Analysis:

  • formed bubbles faster
  • magnesium disappears faster
  • gas produced faster
  • mass lost faster

[6]

Sample question 3 - Higher

Question

A student investigated the rate of reaction between zinc and dilute sulfuric acid:

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

The student carried out two experiments, using the same mass of zinc and the same sized pieces of zinc. The results are shown in the table.

Experiment 1Experiment 2
Concentration of sulfuric acid0.5 mol dm-31.5 mol dm-3
Temperature20°C40°C
Rate of reactionSlowFast

Evaluate these results, explaining the reasons why the rate of reaction in Experiment 2 is faster than the rate of reaction in Experiment 1.

In your answer you should refer to the frequency and energy of collisions between particles. [6 marks]

General points:

  • reactions occur when particles collide
  • more frequent collisions cause higher rate of reaction
  • mass and size of zinc pieces stay the same so no effect on rate of reaction
  • because surface area stays the same
  • two factors have been altered in the same experiment
  • cannot be certain of effect of each

Concentration:

  • experiment 2 higher/triple concentration of acid
  • so more particles (in same volume)
  • so more frequent collisions between particles
  • more successful collisions

Temperature:

  • experiment 2 higher temperature
  • particles move faster
  • particles have more energy
  • so more frequent collisions between particles (so increased rate)
  • more successful collisions
  • so more energetic collisions between particles
  • more particles have enough energy to react (activation energy) when they collide

[6]

Sample question 4 - Higher

Question

Reactions can occur when particles collide.

Rates of reactions can be altered by changing conditions.

Explain how the rate of reaction between a solid and a liquid is altered by reducing the size of the pieces of solid and by increasing the temperature of the liquid. [6 marks]

Your answer should include the following:

Smaller pieces of solid:

  • of same mass
  • have larger surface area to volume ratios
  • so more frequent collisions
  • so higher rate of reaction

Higher temperature:

  • particles move faster
  • more frequent collisions
  • particles have more energy
  • more collisions have required energy to react/activation energy
  • more collisions successful
  • higher rate of reaction

[6]