Req practicals P2

• 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 does the cloudiness in the disappearing cross experiment indicate?

  The formation of solid sulfur in the solution
• What is turbidity in scientific terms?

  Cloudiness of a 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 based on visibility of the cross
• 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 the volume of hydrogen gas measured in the second method?

  Using an upturned measuring cylinder in water
• What do you do every 10 seconds during the gas measurement experiment?

  Measure the volume of hydrogen gas produced
• What conclusion can be drawn from both experiments regarding concentration?

  Higher concentration leads to faster reactions
• Why can the finding about concentration be considered reproducible?

  It is confirmed by two different experiments
• 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. Swirl and start the stopwatch.
  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 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 acid and start stopwatch.
  5. Measure hydrogen gas volume every 10 seconds.
  6. Repeat with different acid concentrations.