Solubility

Three interactions involved in solubility are the intermolecular forces between: - solute molecules - solvent molecules - solute and solvent molecules

When all 3 types of IMFs are about the same strength the solute dissolves freely in the solvent. E.g. Wax mixes freely with cyclohexane because all the IMFs involved are London forces.

Hydrocarbons do not dissolve in water Hydrocarbons do not dissolve in water. The non-polar molecules can separate easily, but the strong H-bonds between water molecules act as a barrier, keeping out molecules that cannot form H-bonds. This is also true for polar molecules such as halogenoalkanes.

Small alcohols are miscible with water Small alcohols are miscible with water. The longer the hydrocarbon chain the less miscible the alcohol in water. Why is this?

Why does salt dissolve in water? The value of the lattice energy for sodium chloride shows that a large amount of energy is needed to separate the ions from a crystal.

Ions are strongly hydrated by polar water molecules Ions are strongly hydrated by polar water molecules. Water molecules cluster round the ions and bind to them. The energy released when this happens is enough to compensate for the energy needed to overcome the ionic bonding between ions.

Why are some salts insoluble in water?

Practical 2.2

Homework: Define: solute, solvent, solution, saturated solution, solubility Write up your practical in your booklet Revise for test