Question

What are 3 interactions that affect solubility, and how they affect solubility?

Answer 1

The interactions or the forces that operate between the solute molecules and the solvent molecules help to improve the solubility of the solute in the solvent. There are three main types of interactions that act to increase the solubility of the solute in the solvent.

a) Ion-dipole or dipole-dipole interactions:

A polar solvent like water, H₂O or an aqueous acid like HCl exists as a dipole,.i.e, there is polarization in the molecule with one of the atoms being positively polarized and the other one negatively polarized (for example, in H₂O, the H and O atoms are positively and negatively polarized). When an ionic compound like NaCl is dissolved in water, the solid compound (NaCl) decomposes into opposite ions. The positive ions (Na⁺) are stabilized by solvation with the negative pole of the solvent (O end) while the negative ions (Cl^-) are stabilized by solvation with the positive end of the solvent (H end). The above is an example of ion-dipole interaction.

Dipole-dipole interactions operate between a polar solvent like H₂O and a polar (non-ionic) molecule like HCl gas (HCl gas doesn’t ionize).

b) Hydrogen Bonding Interactions:

Hydrogen bonds are formed between a solvent containing X-H (X = N, O or F) group and a molecule containing X (X = N, O or F). For example, sugar, C₆H₁₂O₆ solubilizes in water due to hydrogen bonding interactions.

c) Dispersion forces:

Dispersion forces act between non-polar molecules. A non-polar solute like benzene can dissolve in a non-polar solvent like hexane due to dispersion forces.