Required practical 7 - measuring the rate of reaction

Outline of the method for the Iodine clock:

• In a smaller beaker have H2O2

• In a larger beaker have H2SO4 + KI + Na2S2O3 + starch

• Mix the smaller beaker to the larger beaker, and start the stock watch immediately, stop the timer when the colour change turns blue-black

• Repeat the experiment by varying the concentration of KI and water - but everything else remains the same.

• Then in a separate table have the volume of KI and the rate (1/time)

• Then determine the rate order.

Practical considerations for Iodine clock:

• Use wet equipment: Any remaining water will dillute the concentration of the reactants and effect the rate of reaction

• Temperature changes: any changes in the temperature effects the rate of the reaction, so make sure to repeat all the experiments under constant temperature using water bath

• Colour change is subjective and reaction time of humans can effect the reading when they stop the stockwatch.

Outline the method: measuring rate using volume of gas

• Pour 40 cm cubed of HCl into a conical flask

• Clamp a syringe and the plunger is pushed all the way in

• Get a magnesium strip and place in the conical flask, and quickly place a bun and start stock watch

• As the gas is produced this will increase the pressure and push the plunger giving a reading on the volume of gas.

• Every 30 seconds record the volume of gas produced and record

• Repeat the experiements under same temperature, and pressure and surface area of magnesium ribbon but DIFFERENT concentration of hydrochloric acid.

• Plot a graph of volume of hydrogen produced on y-axis against time in seconds on x-axis for both concentrations of hydrochloric acid

• Draw a tangent at t = 0s and find gradient to find intial rate and compare these values to find the reaction order.

Other ways of measuring the rate of reaction:

• Measuring the mass lost

• Measuring pH

• Quenching: When a reaction mixture is sampled at different times, but cooling/ diluting or neutralising the reaction. Then titrating the solution to find the concentrations of reagent present

• colorimeter where the absorbance is proportional to the concentration of Iodine.