Required Practical 5:Rates of Reaction

• What is a hypothesis in scientific terms?

  It is a proposal that could explain a fact or observation and must be testable.
• What is the purpose of the disappearing cross reaction experiment?

  • To explore the effect of concentration on the rate of a reaction
  • To observe the cloudiness (turbidity) produced by the reaction
• What happens when sodium thiosulfate reacts with hydrochloric acid?

  It produces sulfur, making the solution go cloudy.
• What is the method for conducting the disappearing cross experiment?

  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 and swirl the solution.
  4. Start a stopwatch and observe the solution.
  5. Stop the clock when the cross is no longer visible.
  6. Repeat with lower concentrations and calculate mean values.
• What is reproducibility in scientific measurements?

  It means the measurement can be repeated with consistent results.
• What is a potential issue with the disappearing cross experiment related to human factors?

  Different eyesight among individuals can lead to inconsistent results.
• What is the second method for investigating the effect of concentration on reaction rate?

  • Measure the volume of gas produced by a reaction.
  • Use magnesium and hydrochloric acid to produce hydrogen gas.
• What is the method for measuring the volume of gas produced in the second experiment?

  1. Place 50 cm³ of hydrochloric acid in a conical flask.
  2. Attach a delivery tube to the flask.
  3. Submerge the delivery tube in water with an upturned measuring cylinder.
  4. Add magnesium and start the stopwatch.
  5. Measure the volume of hydrogen gas every 10 seconds.
• What conclusion can be drawn from both experiments regarding concentration and reaction rate?

  Greater concentration leads to faster reaction rates.
• Why is it important that the finding about concentration and reaction rate is reproducible?

  • It confirms the reliability of the results.
  • It strengthens the validity of the scientific conclusion.