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Lattice enthalpy

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Question 2

A researcher plans to determine the standard enthalpy change of hydration of calcium ions, ΔhydH(Ca2+)\Delta_{\text{hyd}}H(\text{Ca}^{2+})Δhyd​H(Ca2+). From data tables, the researcher finds the following information:

  • Lattice enthalpy of calcium chloride, ΔLEH(CaCl2)=−2258 kJ mol−1\Delta_{\text{LE}}H(\text{CaCl}_2) = -2258\text{ kJ mol}^{-1}ΔLE​H(CaCl2​)=−2258 kJ mol−1
  • Enthalpy change of hydration of chloride ions, ΔhydH(Cl−)=−363 kJ mol−1\Delta_{\text{hyd}}H(\text{Cl}^-) = -363\text{ kJ mol}^{-1}Δhyd​H(Cl−)=−363 kJ mol−1

The researcher carries out an experiment to determine the enthalpy change of solution of calcium chloride using the following method:

  1. Weigh a bottle containing anhydrous calcium chloride.
  2. Weigh a polystyrene cup.
  3. Add water to the polystyrene cup and record its initial temperature.
  4. Add the calcium chloride, stir thoroughly, and record the maximum temperature reached.
  5. Weigh the empty bottle and weigh the polystyrene cup with the final solution.

Experimental Readings:

  • Mass of bottle + calcium chloride = 28.34 g28.34\text{ g}28.34 g
  • Mass of empty bottle = 19.46 g19.46\text{ g}19.46 g
  • Mass of polystyrene cup = 25.12 g25.12\text{ g}25.12 g
  • Mass of polystyrene cup + final solution = 130.12 g130.12\text{ g}130.12 g
  • Initial temperature of water = 21.2∘C21.2^{\circ}\text{C}21.2∘C
  • Maximum temperature of final solution = 35.6∘C35.6^{\circ}\text{C}35.6∘C

Calculate the enthalpy change of solution of calcium chloride and determine the enthalpy change of hydration of calcium ions. Show your working, including an energy cycle linking the energy changes.

Assume that the specific heat capacity, ccc, of the solution is 4.18 J g−1 K−14.18\text{ J g}^{-1}\text{ K}^{-1}4.18 J g−1 K−1 and the molar mass of CaCl2\text{CaCl}_2CaCl2​ is 111.0 g mol−1111.0\text{ g mol}^{-1}111.0 g mol−1.

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Markscheme

Lattice enthalpy Questions

  1. A Level
  2. /Chemistry
  3. /Lattice enthalpy

7 exam-style questions on OCR A A Level Chemistry Lattice enthalpy. Each one has a worked solution and a mark scheme showing where the marks go.

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