Waterinsoluble

Waterinsoluble substances dissolve very little in water. As a qualitative term, water insolubility is defined for a given temperature by a very low solubility, often below about 0.01 g per 100 mL of water at room temperature, though thresholds vary.

Why some substances are water-insoluble: Ionic solids dissolve if hydration energy overcomes lattice energy; many ionic compounds have high lattice energy and low hydration energy, leading to low solubility. Nonpolar covalent molecules lack strong interactions with water and are dominated by hydrophobic forces, resulting in poor dissolution. Temperature can alter solubility: some solids become more soluble with heat, others less so, depending on the dissolution enthalpy.

Common examples: fats and oils (triglycerides), waxes, and many hydrocarbons are water-insoluble. Some inorganic solids, such as barium sulfate or calcium carbonate, are sparingly soluble in water. Solubility is often described as sparingly soluble or practically insoluble in water.

Implications and applications: Water insolubility affects the bioavailability of drugs, environmental transport, and industrial processing. Formulation strategies to improve solubility include creating salts or prodrugs, using co-solvents or surfactants, reducing particle size, and employing complexation or solid dispersions.

See also: hydrophobicity, solubility, amphiphile.