Chloride salts are soluble, except which of the following?

• A. Silver Chloride (AgCl)
• B. Sodium Chloride (NaCl)
• C. Potassium Chloride (KCl)
• D. Calcium Chloride (CaCl2)

Answer: (A)

Chloride salts generally dissolve because water is able to overcome the forces holding the ions together in the solid lattice, pulling Na+, K+, Ca2+ and Cl− apart and surrounding them with water molecules. Silver chloride behaves differently because its lattice energy is comparatively high—the Ag+ ion is small and highly charged, so the solid AgCl is quite stable. The energy released when water molecules hydrate the ions isn’t enough to break that lattice, so AgCl remains mostly undissolved. In fact, AgCl has a very small solubility product, meaning it dissolves only a tiny amount. The other chlorides listed—sodium chloride, potassium chloride, and calcium chloride—dissolve readily in water, so the exception is silver chloride.