Enthalpies of Solution & Hydration (Cambridge (CIE) A Level Chemistry): Exam Questions

This question focuses on the enthalpy of hydration of fluoride compounds.

i) Define the term enthalpy of hydration in relation to a fluoride ion.

ii) State whether the hydration of a fluoride ion is an exothermic or endothermic process. Explain your answer.

The enthalpy of hydration of the fluoride and chloride ions are -524 kJ mol^-1 and -364 kJ mol^-1.

Explain why the value for the enthalpy of hydration for the fluoride ion is more negative than that for the chloride ion.

Use the enthalpy values in Table 2.1 to suggest why there is a difference between the hydration values of calcium ions and sodium ions.

Table 2.1

The ionic compound calcium bromide, CaBr₂, is used in photography and medicine.

Explain, in terms of electrons, how it is formed from its atoms.

Table 3.1 below gives data for the ionic compound calcium bromide, CaBr₂. 

i) Define the term enthalpy of lattice formation.

[2]

Table 3.1 

ii) Using Table 3.1, calculate the enthalpy of hydration of the calcium ion.

enthalpy of hydration of the calcium ion = ........................ kJ mol^–1

 [2]

Potassium fluoride is also an ionic compound with a wide range of uses.

Use the data in Table 3.2 to calculate the enthalpy of solution of potassium fluoride. 

Table 3.2