What is the trend for the solubility of Group 2 sulfates in water as you move down the group?

What is the trend for the solubility of Group 2 sulfates in water as you move down the group?

• A. Solubility decreases down the group
• B. Solubility increases down the group
• C. Solubility remains constant down the group
• D. Solubility varies irregularly down the group

Answer: (B)

Solubility depends on the balance between lattice energy of the solid and the hydration energy released when the ions are solvated in water. As you move down Group 2, the cation gets larger, so its hydration energy becomes less exothermic (water binds less strongly to the ion). While lattice energy also changes with size, the decrease in hydration energy dominates for Group 2 sulfates. This makes the dissolution process less favorable overall, so the sulfates become less soluble as you go down the group. In practice, BeSO4 and MgSO4 are relatively soluble, while CaSO4 is only sparingly soluble and SrSO4 and BaSO4 are very sparingly or practically insoluble.

Solubility depends on the balance between lattice energy of the solid and the hydration energy released when the ions are solvated in water. As you move down Group 2, the cation gets larger, so its hydration energy becomes less exothermic (water binds less strongly to the ion). While lattice energy also changes with size, the decrease in hydration energy dominates for Group 2 sulfates. This makes the dissolution process less favorable overall, so the sulfates become less soluble as you go down the group. In practice, BeSO4 and MgSO4 are relatively soluble, while CaSO4 is only sparingly soluble and SrSO4 and BaSO4 are very sparingly or practically insoluble.