 Ionic solid (NaCl) |
 Metallic solid (Cu) |
 Covalent network solid (SiO2) |
 Molecular solid (I2) |
It is difficult to predict, with certainty, the solubility of a given substance in a particular solvent.
However it is possible to make educated guesses based on general guidelines which also give insight into the nature of the dissolving process in terms of the ions, atoms and molecules present in the solute and the solvent.
However it is possible to make educated guesses based on general guidelines which also give insight into the nature of the dissolving process in terms of the ions, atoms and molecules present in the solute and the solvent.
Solvents can be classified as polar (H2O) or non-polar (CCl4, CH3CH2CH2CH2CH2CH3).
A general solubility guideline is that like dissolves like. This implies that
polar substances dissolve in polar solvents AND
non-polar substances dissolve in non-polar solvents
non-polar substances dissolve in non-polar solvents
Polar substances are
molecular substances where there is an assymmetric distribution of electrons leading to partial negative and positive charges AND
ionic solids where the particles are charged.
Nonpolar substances exist as molecules where the electron distribution is uniform or nearly so (as it is in non-polar solvents or I2).ionic solids where the particles are charged.
In general, covalent network solids and metallic solids are insoluble in either polar or non-polar solvents.
The insolubility is due to the strong attractive forces between the particles in the lattice of metallic and covalent network solids.
It should be noted that the solutions in this module are those where it is possible to recover both the solute and the solvent by, for example, evaporation of the solvent.
Dissolving may also occur due to a reaction between the substance and the solvent. Some metals and some nonpolar molecular substances dissolve in aqueous acid (or even in water) because they react with water to form a different chemical species that has a higher solubility. In these cases when the solvent is evaporated, the solute is not the same as the substance that dissolved.