Problem 3.3: Sodium chloride dissolves readily in water

From Chapter 3 Problem Set. Level 1: Conceptual Mastery.

Question

Sodium chloride dissolves readily in water while calcium carbonate dissolves reluctantly. Using the language of lattice energy and hydration energy, explain why.

Answer

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Sodium chloride has a manageable lattice cost, sufficient hydration payoff, and often favorable entropy. Dissolution is favored under normal conditions. Calcium carbonate has a much higher lattice cost because calcium and carbonate bind strongly in a stable crystal structure. Water can hydrate the separated ions, but the payoff is often conditional and not enough to overcome the strength of the lattice, especially as temperature, pH, calcium, alkalinity, and carbon dioxide shift the balance toward solid scale.