Question

How is the trend in the solubilities of fluorides and hydroxides different from that of sulphates of the alkaline earth metals?

Answer 1

Hydroxides of Alkali Earth MetalsThe hydroxides of Ca, Sr & Ba are obtained either by treating the metal with cold water or by reacting the corresponding oxides with water. The reaction of these oxides with H2O is also sometimes called as slaking.M + 2H2O  →  M (OH)2 + H2 ( M = Ca, Sr, Ba)MO + H2O → M (OH)2 (M = Ca, Sr, Ba)                            Be(OH)2 and Mg(OH)2 being insoluble are obtained from suitable metal ion solutions by precipitation with OH- ions.BeCI2 + 2NaOH → Be (OH)2 ↓ + 2NaCI               MgSO4 + 2NaOH → Mg (OH)2 ↓ + Na2SO4  

Answer 2

Hey dear,

● Answer -
- Going down the group, atomic radius of alkaline earth metals increase.
- This is followed by decrease in lattice energy but hydration enthalpy of cation is unchanged.
- Therefore, solubility of sulphates of alkaline earth metals increases down the group.
- On the other hand, solubility of hydroxides & fluorides decreases down the group.


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