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How To Set Up GCSE Chemistry Required Practical – Rates of Reaction – Activity 1

How To Set Up GCSE Chemistry Required Practical – Rates of Reaction – Activity 1

In this short video, Emma Dent shows how to demonstrate the AQA Required Practical – Rates of Reaction – Activity 1.

In this experiment, we are investigating how changes in the concentration of reactants affect the rate of reaction. This is typically explored using the reaction between sodium thiosulfate and hydrochloric acid, with the formation of a sulphur precipitate leading to a change in visibility that indicates the reaction progress.

This practical demonstrates first-hand collision theory, which is a concept in chemistry that explains how reaction rates are influenced by the frequency and energy of collisions between reactant molecules. Students can determine how changes in reactant concentration affect the rate of a chemical reaction. The formation of the sulphur precipitate in this experiment serves as a visual cue for measuring reaction progress.



You will need:

  • 40g/dm3 Sodium thiosulfate solution
  • Hydrochloric acid solution (1 M)
  • Distilled water (for dilution)
  • Conical flasks (100 mL or 250 mL)
  • Measuring cylinders or burettes for accurate measurement
  • Stopwatch or timer
  • White paper with a clear mark or a black cross
  • Safety equipment (safety goggles, lab coat, gloves)
  • Pipettes or burettes for precise measurements (optional but helpful)
  • Stirring rod or magnetic stirrer (optional).



  1. Measure 10 cm³ of sodium thiosulfate solution into a conical flask. Add 40 cm³ of water to dilute it. The final concentration should be 8 g/cm³.
  2. Place the conical flask on a flat surface with a black cross underneath.
  3. Use another measuring cylinder (or wash the previous one) to easurme 10 cm³ of dilute hydrochloric acid.
  4. Quickly add the acid to the conical flask, immediately start the stopwatch or timer and gently swirl the flask.
  5. Look down through the top of the flask and watch the cross. Stop the stopwatch or timer when the cross becomes invisible. Record the time taken for the reaction and do two more repeats for this concentration.
  6. Clean the equipment and repeat steps 1-6 changing the concentration of sodium thiosulphate each time as below:
    20 ml sodium thiosulfate + 30 ml water (concentration 16 g/dm3)
    30 ml sodium thiosulfate + 20 ml water (concentration 24 g/dm3)
    40 ml sodium thiosulfate + 10 ml water (concentration 32 g/dm3)
    50 ml sodium thiosulfate + no water (concentration 40 g/dm3).
  7. Plot your data and draw a smooth curved line of best fit

All health and safety measures are the responsibility of the teacher doing the demonstration. A thorough risk assessment should be carried out and guidance procedures followed. It is suggested that you practice before demonstration in front of a class.


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