Calorimetry experiments for determining the enthalpy changes of reactions
5 marks · HardDescribe how you would carry out a calorimetry experiment to determine the enthalpy change of a displacement reaction between magnesium and copper(II) sulfate solution in a school laboratory. Your answer should refer to apparatus, measurements, and how you would ensure reliable results.
State the main pieces of apparatus you would use for this experiment.
Describe the basic procedure for mixing the reactants and measuring the temperature change.
Suggest two ways to improve the reliability or accuracy of the results in this experiment.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) polystyrene cup, thermometer, measuring cylinder, balance, beaker, stirring rod · must show polystyrene cup/cup, thermometer, measuring cylinder, balance, stirring rod
(b) Add a known volume of copper(II) sulfate solution to the polystyrene cup. Measure and record the initial temperature. Add a known mass of magnesium. Stir the mixture and record the maximum temperature reached after the reaction. · must show record initial temperature, add magnesium to solution, stir, record maximum temperature
(c) Suggestions include: (1) Repeat the experiment and use the average value. (2) Insulate the cup or use a lid to reduce heat loss. (3) Stir the mixture well to ensure uniform temperature. · must show repeat and average readings, insulate or use lid, stir thoroughly
Common mistakes: Not mentioning stirring; Not measuring initial/final temperatures; Not shielding from drafts
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States appropriate main apparatus (e.g., polystyrene cup, thermometer, measuring cylinder, balance, stirring rod).
M1 (b) · 1 mark · Describes adding the copper(II) sulfate solution and recording the initial temperature.
M2 (b) · 1 mark · Describes adding magnesium, stirring, and measuring the maximum temperature.
B2 (c) · 1 mark · Suggests one way to improve reliability or accuracy (e.g., repeat and average, insulate cup, use lid, stir well).
B3 (c) · 1 mark · Suggests a second, different way to improve reliability or accuracy.
Worked solution
a) Apparatus: polystyrene cup, thermometer, measuring cylinder, balance, beaker, stirring rod.
b) Procedure: Add a known volume of copper(II) sulfate solution to the polystyrene cup and record its initial temperature. Weigh a known mass of magnesium, add it to the solution, and stir with the stirring rod. Measure and record the maximum temperature reached after the reaction is complete.
c) Two ways to improve reliability or accuracy: - Repeat the experiment several times and calculate an average. - Use a lid on the cup or further insulate the setup to reduce heat loss to the surroundings.