P2 rates of reaction

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

  How to carry out a practical investigation
• What is a hypothesis in science?

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

  Sodium thiosulfate with hydrochloric acid
• What does the solid sulfur produced in the reaction cause?

  It makes the solution go cloudy
• What is turbidity in scientific terms?

  Cloudiness of a solution
• What is the first step in the disappearing cross experiment method?

  Put 10 cm³ of sodium thiosulfate in a flask
• What do you do after swirling the solution in the disappearing cross experiment?

  Look down through the top of the flask
• When do you stop the stopwatch in the disappearing cross experiment?

  When you can no longer see the cross
• What should you do with anomalous results when calculating the mean?

  Do not include them in the calculation
• What does reproducibility mean in measurements?

  Results can be repeated with the same outcome
• Why might different people get different results in the disappearing cross experiment?

  Because of variations in eyesight
• What is the second method for measuring reaction rates discussed?

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

  Hydrogen gas
• What is the first step in the gas volume measurement method?

  Place 50 cm³ of hydrochloric acid in a flask
• What do you use to measure the volume of hydrogen gas produced?

  A measuring cylinder filled with water
• How often do you measure the volume of hydrogen gas during the experiment?

  Every 10 seconds
• What conclusion can be drawn from both experiments regarding concentration?

  Higher concentration leads to faster reactions
• Why is the finding about concentration reproducible?

  It is shown by two different experiments
• What are the steps in the disappearing cross experiment?

  1. Measure 10 cm³ sodium thiosulfate into a flask.
  2. Place the flask on a printed black cross.
  3. Add 10 cm³ hydrochloric acid and swirl.
  4. Start the stopwatch and observe the cross.
  5. Stop the clock when the cross is no longer visible.
  6. Repeat with lower concentrations and calculate mean values.
• What are the steps in measuring gas volume with magnesium and hydrochloric acid?

  1. Measure 50 cm³ hydrochloric acid into a 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.
  5. Start the stopwatch and measure gas volume every 10 seconds.
  6. Repeat with different concentrations of hydrochloric acid.