The questions below are all on calorimetry. Each page has only one question on it, and the mark scheme for each question is on the page that immediately follows. A printable copy of the questions can be found here.
Question 19
A 5.00 g sample of potassium chloride was added to 50.0 g of water initially at 20.0 °C. The mixture was stirred and as the potassium chloride dissolved, the temperature of the solution decreased.
(a) Describe the steps you would take to determine an accurate minimum temperature that is not influenced by heat from the surroundings.
(4)
(b) The temperature of the water decreased to 14.6 °C.
Calculate a value, in kJ mol−1, for the enthalpy of solution of potassium chloride.
You should assume that only the 50.0 g of water changes in temperature and that the specific heat capacity of water is 4.18 J K−1 g−1.
Give your answer to the appropriate number of significant figures.
(4)
(c) The enthalpy of solution of calcium chloride is −82.9 kJ mol−1.
The enthalpies of hydration for calcium ions and chloride ions are −1650 and −364 kJ mol−1, respectively.
Use these values to calculate a value for the lattice enthalpy of dissociation of calcium chloride.
(2)
(d) Explain why your answer to part (c) is different from the lattice enthalpy of dissociation for magnesium chloride.
(2)
(Total 12 marks)