rp7

• What is the title of Required Practical 7 in AQA Chemistry A-level?

  Measuring the rate of reaction
• What is the initial rate method used in the iodine clock experiment?

  It measures the rate of reaction using iodine
• What are the reactants in the iodine clock experiment?

  Hydrogen peroxide and iodide ions
• What is the role of thiosulfate ions in the iodine clock experiment?

  They remove iodine as it forms
• What are the steps in the iodine clock experiment method?

  1. Rinse burette with potassium iodide.
  2. Transfer hydrogen peroxide to a beaker.
  3. Add sulfuric acid to a beaker.
  4. Add distilled water to the beaker.
  5. Add starch solution to the beaker.
  6. Add potassium iodide solution to the mixture.
  7. Add sodium thiosulfate solution to the mixture.
  8. Stir and add hydrogen peroxide, starting the timer.
  9. Stop timer when mixture turns blue-black.
  10. Rinse and dry the beaker.
  11. Repeat with different potassium iodide concentrations.
  12. Plot graph of initial rate versus concentration.
• Why is it important to rinse the burette with potassium iodide before use?

  To ensure accurate measurement of solutions
• What should be done to the beaker before adding hydrogen peroxide?

  It should be clean and dry
• What is the purpose of adding starch solution in the iodine clock experiment?

  It indicates the presence of iodine by turning blue-black
• How much potassium iodide solution is added to the mixture?

  5.0 cm​3
• What is the significance of repeating the experiment with different concentrations of potassium iodide?

  To determine the order of reaction
• What improvement can be made to minimize human error in timing during the iodine clock experiment?

  Use a colorimeter
• What is the first step in the continuous monitoring method?

  Add hydrochloric acid to a conical flask
• What should be done after adding magnesium ribbon to the conical flask in the continuous monitoring method?

  Place the bung firmly and start the timer
• How often should the volume of hydrogen gas be recorded in the continuous monitoring method?

  Every 15 seconds
• Why is measuring the initial rate preferred in reactions?

  Because concentrations are known at the start
• What are the methods for following the reaction in the experiments?

  • Colorimeter: Measures absorbance related to concentration.
  • Quenching: Samples are taken and stopped by cooling or diluting.
  • Measuring mass lost.
  • Measuring pH.
• What is the purpose of plotting a graph of volume of hydrogen produced against time?

  To analyze the reaction rate at different concentrations
• What should be done to each line of best fit on the graph?

  Draw a tangent at time t = 0 s
• How can the initial rate of each reaction be deduced from the graph?

  By calculating the gradient of each tangent
• What is a limitation of a typical gas syringe in the continuous monitoring method?

  It only measures 100 cm​3 of gas
• Why is it important to calculate reactant quantities carefully in the continuous monitoring method?

  To avoid exceeding the gas syringe capacity
• What happens if one reactant is kept in large excess?

  It appears not to affect the rate
• What is the purpose of quenching in reaction monitoring?

  To stop the reaction for analysis
• How can aliquots be used in the quenching method?

  They can be sampled without disturbing the reaction
• What is one method of measuring the reaction rate besides gas collection?

  Measuring pH
• What is required to calculate the exact concentration of iodine using a colorimeter?

  A calibration graph
• What is the relationship between absorbance and concentration in the colorimeter method?

  Absorbance is proportional to concentration