A quick note on solvents

This seems just the right moment to refresh your understanding of the different types off solvent so that you can confidently explain why ionic compounds dissolve so easily in water (a polar protic solvent) but are not so keen on DMSO (apolar aprotic solvent).

Almost all of the chemical reactions we study take place in a solvent, often water, and the choice of solvent can have a significant effect on the rate and the products of a reaction. 

Many ionic compounds dissolve readily in water (a polar solvent) to form aqueous solutions but this is certainly not the case for all and no ionic compound will dissolve in a non-polar solvent. Wax will dissolve in hexane (a non-polar solvent) but not in water or ethanol.  Clearly the types of interactions that are possible between solute and solvent are key. 

Polar solvents that are capable of forming hydrogen bonds between themselves, and ion-dipole bonds with anions and cations are more formally known as polar ‘protic’ solvents – water and ethanol are good examples.

Polar ‘aprotic’ solvents such as DMSO (dimethylsulfoxide) typically have an oxygen or nitrogen atom with a lone pair of electrons that allows them to interact with cations, but  they don’t have a highly 𝛿+ hydrogen atom so are unable to form hydrogen bonds with anions.

Non-polar solvents such as hexane have neither 𝛿+ hydrogen atoms or dipoles so are very poor at solvating ions. They are able to form extensive instantaneous dipole – induced dipole intermolecular forces / London forces with other non-polar molecules and are good solvent choices for hydrocarbons. 

Leave a Reply

Your email address will not be published. Required fields are marked *