RP5 Rate Of Reaction

• Three ways of measuring the rate of a reaction

  • Observe how quickly a precipitate forms
  • Measure the change in mass
  • Measure the volume of gas given off
• How to calculate the rate of reaction

  Rate of Reaction = Amount of product formed or reactant used / Time
• How to measure the rate of reaction if a precipitate is produced

  1. Place piece of paper with a black cross below the reaction vessel and observe this cross through the solution

  2. Measure how long it takes for the cross to disappear
• How to measure the rate of reaction if the coloured reactants form a colourless solution

  Time how long it takes for the reactants to turn colourless
• Precipitate and colour change rate experiments

  • They are very subjective - people might disagree over the exact point when the mark disappears or the solution changes colour
• How to measure the rate of reaction when there is a change in mass

  1. Carry out the experiment on a mass balance:

  2. Measure initial mass

  3. Combine reactants

  4. Take measurements of the mass at regular intervals as the reactants react

  5. Rate = change in mass ÷ time
• How to measure the rate of reaction when a gas is given off

  1. Add reactants to a conical flask

  2. Immediately attach a gas syringe to the conical flask with a bung to ensure minimal gas escapes

  3. Take regular measurements of the volume of gas in the gas syringe

  4. Rate = total volume of gas produced ÷ time
• How to find the rate of reaction of a reaction after 30 seconds (Higher)

  1. Plot results on a graph

  2. X axis: time

  3. Y axis: amount of product formed or reactant used

  4. Draw a tangent at 30 seconds and calculate the gradient (change in y ÷ change in x) to calculate the rate of reaction
• How to investigate how HCl concentration affects the rate of reaction when magnesium is added

  1. Place the HCl in a conical flask

  2. Add the magnesium ribbon and quickly fit the bung and gas syringe

  3. Record volume of gas collected every 10 seconds

  4. Repeat with a different concentration of HCl

  5. Compare the rates for each concentration
• How to investigate how sodium thiosulfate concentration affects the rate of reaction when reacted with HCl

  1. Add 30cm3 of sodium thiosulfate to a conical flask

  2. Add 10 cm3 dilute HCl

  3. Measure the time it takes for the cross to disappear

  4. Repeat three times for mean time

  5. Repeat the experiment with different concentrations of sodium thiosulfate

  6. Compare the times for each experiment