Rates of Reaction - The disappearing cross reaction

• What are some factors that affect rate of reaction?


  Temperature

  reactant concentrations

  presence or absence of a catalyst
• What is the first step in the Disappearing Cross Reaction method?

  Use a measuring cylinder to put 10 cm³ of sodium thiosulfate solution into a conical flask.
• Why is the conical flask placed on a printed black cross?

  To observe when the cross becomes no longer visible due to the cloudiness of the solution.
• How much hydrochloric acid is added to the conical flask?

  10 cm³ of hydrochloric acid.
• What should you do after adding hydrochloric acid to the conical flask?

  Swirl the solution and start a stopwatch.
• What indicates that the reaction has occurred in the Disappearing Cross Reaction?

  The solution turns cloudy, making the cross no longer visible.
• When should you stop the stopwatch during the experiment?

  When the cross is no longer visible.
• What should you do after completing the experiment once?

  Carry out the experiment again using lower concentrations of sodium thiosulfate solution.
• What is the next step after repeating the experiment with different concentrations?

  Calculate mean values for each concentration of sodium thiosulfate solution, excluding anomalies.
• What is the overall process of the Disappearing Cross Reaction?

  1. Measure 10 cm³ of sodium thiosulfate solution into a conical flask.
  2. Place the flask on a printed black cross.
  3. Add 10 cm³ of hydrochloric acid to the flask.
  4. Swirl the solution and start the stopwatch.
  5. Observe the solution until the cross is no longer visible.
  6. Stop the stopwatch and record the time.
  7. Repeat with lower concentrations of sodium thiosulfate.
  8. Calculate mean values for each concentration, excluding anomalies.
• What is a negative of this experiment?

  People have different eye sight so the cross may be visible to others for longer - making the results inaccurate
• What does this experiment show?

  Greater the concentration - faster reaction takes place

  This is shown by two different experiments having the same results (reproductible)