Unit – II A
Solution of Solids or Liquids in Liquids:
A solution of Solids in Liquids:
- Dissolution of any substance in a liquid to form solution is governed by the basic principle that the solute-solvent interaction is either similar or greater than solute-solute and solvent-solvent interaction.
- Let us consider dissolution of an ionic solid in water. There is an interionic attraction between the ions of solid. In this case, the cations and anions of the solid get attracted by the opposite ends of water dipoles.
- If the ion-dipole interaction forces are stronger than interionic attraction, the ions are pulled out of crystal lattice and they pass into solution. Formed ions are called hydrated ions.
- Molecular solids dissolve in water on account of their capacity to form hydrogen bonds with water molecules.
- The energy required to dismantle 1 mol of the crystal lattice is called lattice energy (ΔLH). The energy released during hydration is called hydration energy (ΔHydroH).
A solution of Liquids in Liquids:
When two liquids are mixed, there are three possibilities.
- The two components are almost immiscible. It happens when one liquid is polar and other in non-polar. e.g. a mixture of water and benzene.
- The miscibility of the component may be partial. This happens when the intermolecular attraction of one liquid is different from the intermolecular attraction of other liquid. e.g. a mixture of water and ether.
- The two components may be completely miscible. It happens when the two liquids have the same nature. Either both are polar (e.g. a mixture of alcohol and water) or both are non-polar (e.g. a mixture of benzene and hexane).
Characteristics of miscible liquids:
- They are chemically alike.
- Both have same nature.
- The dipole-dipole interaction is stronger.
- Molecular sizes of liquids are approximately same.