Required Practical 5

• What are the steps in the sample method for the concentration rate of reaction required investigation?

  1. Set up the equipment.
  2. Add hydrochloric acid to the flask and swirl.
  3. Start the timer.
  4. Watch the cross through the flask.
  5. Stop the timer when the cross is no longer visible.
  6. Repeat with a different concentration of hydrochloric acid.
• What is the independent variable in the investigation?


  The concentration of the acid
• What is the dependent variable in the investigation?


  The time it takes for the cross to 'disappear'
• What correlation is expected between the concentration of the acid and the time taken for the cross to disappear?

  There should be a correlation where higher acid concentration results in a shorter time for the cross to disappear
• How does the concentration of the acid affect the rate of reaction?

  The higher the concentration of the acid, the faster the rate of reaction
• What safety precautions must be taken during the investigation?

  Eye protection must be used due to corrosive acid
• Why must the temperature be kept below 50°C during the investigation?

  To prevent gas produced from triggering an asthma attack
• What are the potential hazards and risks associated with the investigation?

  • Corrosive acid can damage eyes
  • Produced gas can trigger asthma attacks
  • Temperature must be kept below 50°C
• What is a hypothesis in scientific terms?

  • A proposal that could explain a fact or observation
  • Must be testable
• What is the disappearing cross reaction used for?

  To explore the effect of concentration on the rate of a reaction
• What term do scientists use to describe the cloudiness of a solution?

  Turbidity
• What is the method for the disappearing cross experiment using sodium thiosulfate and hydrochloric acid?

  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 potential problem with the disappearing cross experiment?


  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. Use an upturned measuring cylinder filled with water over the delivery tube.
  5. Add a 3 cm strip of magnesium and start the stopwatch.
  6. Measure the volume of hydrogen gas every 10 seconds until the reaction stops.
• What conclusion can be drawn from both experiments regarding concentration and reaction rate?


  The greater the concentration of a chemical in a reaction, the faster the reaction takes place
• Why can the finding about concentration and reaction rate be considered reproducible?


  Because it is shown by two different experiments
• Why does the solution go cloudy in the disappearing cross experiment?

  The solution goes cloudy because a precipitate is formed
• Name the equipment

  Stopwatch

  
• Name the equipment

  Flask

  
• Name the acid used in this investigation

  Hydrochloric acid

  
• Name the label

  cross

  
• Name the sulfate used

  Sodium thiosulfate

  
• What is the purpose of the required practical on concentration? (rate of reaction?)


  To investigate how changes in concentration affect the rates of

  reactions