What factors affect the solubilty of a substance?

Answer 1

Solubility is a complex and not fully understood phenomenon.

• Firstly it is explained by the type of bonds in the solute (the substance that is dissolving) compared to the type of bonds in the solvent (the substance that the solute dissolves into).

A polar solvent will dissolve solutes that have some polarity in the bonds or are charged in some way. Water has polar oxygen to hydrogen bonds, O-H, so it will dissolve sugar (O-H) or alcohol (O-H) or table salt (Na+ - Cl-) but not oil (no positive - negative centers). Petrol/gasoline has no polar bonds so it will dissolve oil, grease or wax.

• Secondly, the existing bonds in the solute have to break and form new bonds with the solute. There has to be some 'advantage' in terms of energy for the solute to dissolve.
• In addition, the temperature will affect solubility. It is not the case that an increase in temperature always increases solubility.
• Whether there are any other dissolved substances present - 'the common ion effect'.
• Pressure can affect solubility although this is virtually insignificant when it comes to liquids and solids.

Although the terms - soluble, and insoluble are in common usage, it is all about the degree of solubility. Insoluble means that the salt is less soluble than about 1 g per 100 g of solvent. Heavy metal salts would be in this category but need to be avoided by all living things.