3.8 Solubility

Solubility and Dissolution

Solubility is the maximum amount of solute that dissolves in a solvent at a given temperature to form a saturated solution. Dissolution occurs when solute-solvent attractions overcome solute-solute and solvent-solvent attractions. "Like dissolves like": polar/ionic solutes dissolve in polar solvents (like water) via ion-dipole or dipole-dipole forces, while nonpolar solutes dissolve in nonpolar solvents via London dispersion forces.

Ionic Compounds in Water

When an ionic solid dissolves, water molecules surround and stabilize ions through ion-dipole interactions, called hydration. Dissolution depends on the balance between lattice energy (energy holding the ionic solid together) and the energy of hydration (energy released as ions are surrounded by water). If hydration energy sufficiently offsets lattice energy, the compound is soluble.

Factors Affecting Solubility

Temperature generally increases solubility of solids in liquids, but gas solubility in liquids decreases as temperature rises. Pressure significantly affects gas solubility (Henry's Law): higher pressure increases gas solubility in liquids. Molecular size and polarity also matter—larger nonpolar molecules dissolve better in nonpolar solvents.

Key terms

Solubility

The maximum amount of solute that dissolves in a solvent at a given temperature to form a saturated solution.

"Like dissolves like"

Polar/ionic solutes dissolve best in polar solvents; nonpolar solutes dissolve best in nonpolar solvents.

Hydration

The process where water molecules surround and stabilize dissolved ions through ion-dipole interactions.

Lattice energy vs. hydration energy

An ionic compound dissolves when the energy released from hydration sufficiently offsets the lattice energy holding the solid together.

Effect of temperature and pressure on gas solubility

Gas solubility in liquids decreases as temperature rises but increases with higher pressure (Henry's Law).

Try an AP-style question

Which is most soluble in water?

1. C₆H₁₄
2. CCl₄
3. CH₃OH
4. CH₄