Rates of reaction

• Hypothesis


  A proposal that could explain a fact or observation, and must be testable
• Disappearing cross reaction


  1. Use measuring cylinder to put 10 cm3 sodium thiosulfate solution into conical flask

  2. Place conical flask on printed black cross

  3. Add 10 cm3 hydrochloric acid

  4. Swirl solution and start stopwatch

  5. Look down through top of flask until solution turns cloudy, stop clock

  6. Repeat with lower concentrations of sodium thiosulfate

  7. Calculate mean values, excluding anomalous results
• Reproducibility


  A measurement is reproducible if it can be repeated by another person or using a different technique/equipment and still get the same result
• Measuring volume of gas produced

  1. Use measuring cylinder to place 50 cm3 hydrochloric acid into conical flask

  2. Attach conical flask to bung and delivery tube

  3. Place delivery tube into water-filled container

  4. Place upturned measuring cylinder filled with water over delivery tube

  5. Add 3 cm strip of magnesium to hydrochloric acid and start stopwatch

  6. Measure volume of hydrogen gas in measuring cylinder every 10 seconds until no more gas given off

  7. Repeat with different concentrations of hydrochloric acid
• The greater the concentration of a chemical in a reaction, the faster the reaction takes place
• This finding is reproducible as it is shown by two different experiments