What does the term enthalpy change of hydration, $\Delta H^{\circ}_{\text{hyd}}$, mean?
Write an equation to show the $\Delta H^{\circ}_{\text{hyd}}$ of the $\text{Mg}^{2+}$ ion.
Suggest a reason why $\Delta H^{\circ}_{\text{hyd}}$ of the $\text{Mg}^{2+}$ ion is greater than $\Delta H^{\circ}_{\text{hyd}}$ of the $\text{Ca}^{2+}$ ion.
Suggest why it is impossible to determine the enthalpy change of hydration of the oxide ion, $\text{O}^{2-}$.
The enthalpy change of solution for $\text{MgCl}_2$, $\Delta H^{\circ}_{\text{sol}}(\text{MgCl}_2(s))$, is represented by the following equation: $\text{MgCl}_2(s) + \text{aq} \rightarrow \text{Mg}^{2+}(aq) + 2\text{Cl}^-(aq)$. Describe the simple apparatus you could use, and the measurements you would make, in order to determine a value for $\Delta H^{\circ}_{\text{sol}}(\text{MgCl}_2(s))$ in the laboratory.
By constructing relevant thermochemical cycles, use the above data to calculate a value for $\Delta H^{\circ}_{\text{sol}}(\text{MgCl}_2(s))$.
By constructing relevant thermochemical cycles, use the above data to calculate a value for $\Delta H^{\circ}_{\text{hyd}}(\text{Cl}^-(g))$.
Describe and explain how the solubility of magnesium sulfate compares to that of barium sulfate.