PbCl₂ is actually only sparingly soluble in water, not highly soluble—this is a common misconception. At room temperature, only about 10 grams dissolves per liter of water, making it one of the least soluble common chloride salts.
When PbCl₂ does dissolve, it dissociates into Pb²⁺ and Cl⁻ ions. The limited solubility occurs because the lattice energy (energy required to break apart the ionic crystal) is high due to the small size and high charge density of the Pb²⁺ ion. However, water's polarity and hydrogen-bonding ability provide enough hydration energy to overcome this lattice energy—but only partially.
Temperature significantly affects PbCl₂ solubility in an unusual way: it actually increases with temperature, unlike most ionic salts. At 100°C, about 37 grams per liter can dissolve. This inverse temperature behavior for cold water is due to complex interactions between the hydration process and crystal formation dynamics.
The key factors determining solubility are: (1) water's polar nature, which stabilizes separated ions; (2) the hydration energy of Pb²⁺ and Cl⁻ ions; and (3) the opposing lattice energy of the solid crystal. For PbCl₂, the lattice energy is strong enough that water alone cannot dissolve significant amounts, resulting in low but measurable solubility rather than high solubility.