rates of reaction

• What is a hypothesis in science?

  • A proposal that could explain a fact or observation
  • Must be testable
• What experiment is used to explore the effect of concentration on the rate of a reaction?

  The disappearing cross reaction
• What happens when sodium thiosulfate solution reacts with hydrochloric acid?

  It produces sulfur, which makes the solution go cloudy
• What is the term used to describe the cloudiness of a solution?

  Turbidity
• What is the method for the disappearing cross experiment?

  1. Measure 10 cm³ of sodium thiosulfate into a conical flask.
  2. Place the flask on a printed black cross.
  3. Add 10 cm³ of hydrochloric acid and swirl.
  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 measurements?

  A measurement is reproducible if it can be repeated by another person or using different techniques and still yield the same result
• What is a problem with the disappearing cross experiment related to human factors?

  Different people have different eyesight, affecting their ability to see the cross
• What is the second method for investigating the effect of concentration on reaction rate?

  • Measure the volume of gas produced by a reaction
  • Example: Reacting magnesium with hydrochloric acid to produce hydrogen gas
• What is the method for measuring the volume of gas produced in the magnesium and hydrochloric acid reaction?

  1. Measure 50 cm³ of hydrochloric acid into a conical flask.
  2. Attach the flask to a bong and delivery tube.
  3. Place the delivery tube in a water-filled container.
  4. Add a 3 cm strip of magnesium to the acid and start a stopwatch.
  5. Measure the volume of hydrogen gas every 10 seconds until no more gas is produced.
• What is the relationship between concentration and reaction rate as shown by the experiments?

  The greater the concentration of a chemical, the faster the reaction takes place
• What should you do when calculating mean values for concentrations in experiments?

  Do not include any anomalous results
• Why is it important to have reproducible results in experiments?

  • Ensures reliability of findings
  • Confirms that results are not due to random chance