RP7: Measuring the rate of reaction

• What is the reaction rate?


  The reaction rate is the change in reactants or products per unit of time. If the reactants are in solution, the rate will be change in concentration per second and the units: mol dm–3 s–1.
• What is continuous monitoring?


  By recording the amount of product or reactant you have at regular time intervals
• What to use the measure volume of a gas?

  Gas syringe
• Formula to work out rate of reaction


  Change in y/ change in X
• What to do if the gradient is a curve?

  Tangent
• The standard method for continuous monitoring reaction

  1. Add 50 cm3​ o​f known con HCL to a conical flask.
  2. Set up the gas syringe
  3. Add a 6 cm strip of magnesium ribbon to the conical flask, place the bung firmly on top of flask and start timer. Swirl the flask every few seconds.
  4. Record the volume of hydrogen gas collected every 15 seconds for 2.5 minutes.
  5. Alter the concentration of HCl and repeat steps (1) to (4).
• In an experiment to determine the rate of a reaction, the volume of gas produced in the reaction was measured at regular intervals for several minutes.

  (a) State one experimental condition that must be kept constant 


  Temperature
• State one condition, other than temperature and pressure, that would need to be kept constant in this investigation.


  Mass of magnesium
• Which one method could the student use for removing soluble impurities from the sample of magnesium hydroxide that has been separated?


  Wash with water
• Problems with continuous monitoring method


  Some gas may escape

  Mg strips may be different masses/ SA affecting rate of reaction
• How would you analyse the data from a continuous monitoring experiment?

  1. Plot a graph of hydrogen gas (y-axis) against HCL concentration (x-axis). Draw line of best fit
  2. Draw a tangent at t= 0s for each line
  3. Calculate gradient to find rate
  4. Compare rate values