Hydrated copper(II) sulfate, CuSO4⋅5H2O, is sometimes used in instant hot packs. A student conducts three independent calorimetry trials to measure the enthalpy of dissolution of this salt. In each trial, 3.00 g of CuSO4⋅5H2O is added to 100.0 g of water initially at 22.5 °C in a polystyrene cup. Assume the specific heat capacity of the resulting solution equals that of pure water and that heat losses to the surroundings other than the cup are negligible. The cup has negligible heat capacity.
Data Table (temperature in °C):
Trial | Final temperature
1 | 26.7
2 | 26.2
3 | 27.0
(a) For Trial 1, determine the heat released or absorbed by the solution and state its sign.
(b) Using Trial 1, calculate the molar enthalpy of dissolution for CuSO4⋅5H2O.
(c) Compute the average molar enthalpy of dissolution from all three trials.
(d) The accepted literature value is −76kJ mol−1. Calculate the percent error of the student’s average result.
(e) Identify two specific experimental limitations that could account for any discrepancy between the student’s average value and the literature value.