Tue February 07, 2012 By: Avijit Gupta

how does lattice enthalpy influence solubility of alkaline earth metal compounds in water?

Expert Reply
Wed February 08, 2012

As a general rule, for a salt to be able to dissolve in a particular solvent its solvation enthalpy must be greater than its lattice enthalpy so that the latter may be overcome by former.

Among alkaline earth metal hydroxides, the anion being common the cationic radius will influence the lattice enthalpy. Since lattice enthalpy decreases much more than the hydration enthalpy with increasing ionic size, the solubility increases as we go down the group. The solubility of alkaline earth metal carbonates and sulphates in water decrease down the group because the size of anions being much larger compared to cations, the lattice enthalpy will remain almost constant within a particular group. Since the hydration enthalpies decrease down the group solubility will decrease.

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