Required Practical 5: Rates of Reaction

• What should you be able to do by the end of the video?

  Describe a practical investigation
• What is a hypothesis in science?

  A testable proposal explaining observations
• What reaction is used in the disappearing cross experiment?

  Sodium thiosulfate with hydrochloric acid
• What product is formed in the disappearing cross reaction?

  Solid sulfur
• What does turbidity refer to in a solution?

  Cloudiness of the solution
• How do you start the disappearing cross experiment?

  Swirl the solution and start a stopwatch
• Why is reproducibility important in experiments?

  It ensures consistent results across trials
• What issue arises from different people's eyesight in the disappearing cross experiment?

  Results may vary due to visibility differences
• What is the second method for measuring reaction rates?

  Measuring the volume of gas produced
• What gas is produced when magnesium reacts with hydrochloric acid?

  Hydrogen gas
• How is hydrogen gas collected in the second method?

  Using an upturned measuring cylinder in water
• What does the result of both experiments indicate about concentration?

  Higher concentration leads to faster reactions
• What should you do with anomalous results when calculating a mean?

  Do not include them
• What are the steps in the disappearing cross experiment?

  1. Measure 10 cm³ sodium thiosulfate.
  2. Place in a conical flask over a black cross.
  3. Add 10 cm³ hydrochloric acid.
  4. Start stopwatch and observe cloudiness.
  5. Stop when the cross is no longer visible.
  6. Repeat with lower concentrations.
  7. Calculate mean values, excluding anomalies.
• What are the steps in the gas volume measurement experiment?

  1. Measure 50 cm³ hydrochloric acid.
  2. Attach conical flask to a bong and delivery tube.
  3. Place delivery tube in water-filled container.
  4. Add magnesium strip to hydrochloric acid.
  5. Start stopwatch and measure gas volume every 10 seconds.
  6. Repeat with different acid concentrations.