The purpose of this experiment is to determine the enthalpy change for the displacement reaction:
By adding an excess of zinc powder to a measured amount of aqueous copper(II) sulfate, and measuring the temperature change over a period of time, you can then calculate the enthalpy change for the reaction.
- safety glasses
- measuring cylinder, 25 cm3
- pipette filler
- polystyrene cup with lid
- copper(II) sulphate solution, 1.00 mol dm-3
- weighing boat
- zinc powder
- thermometer, 0 – 100°C (0.2 °C graduations)
- Add 25.0 cm3 of the copper(II) sulphate solution into a polystyrene cup.
- Weigh about 6g of zinc powder in the weighing bottle. Since this is an excess, there is no need to be accurate.
- Put the thermometer through the hole in the lid, stir and record the temperature to the nearest 0.1°C every 30 seconds for 2 minutes.
- At precisely 3 minutes, add the zinc powder to the cup.
- Continue stirring and record the temperature every 30 seconds for an additional 6 minutes. Recording each value in the results table.
- Plot the temperature (y-axis) against time (x-axis).
- Extrapolate the curve to when the metal was added to the solution (3 minutes). This is to establish the theoretical maximum temperature rise.
- Calculate the enthalpy change for the quantities used, making the same assumptions as in the preceding exercise.
- Calculate the enthalpy change for one mole of Zn (s) and CuS04 (aq), and write the thermochemical equation for the reaction.
- Compare your result with the accepted value of -217 kJ mol-1 by calculating the percentage error in your answer:
- List some possible reasons for any difference between your value and the accepted value.