Question

Explain why polar substances dissolve in water while nonpolar substances do not.

Short answer

The polar substances have weaker intermolecular forces of attraction. Hence they can be easily attracted to the water molecules, whereas the non-polar substances have stronger intermolecular forces of attraction; hence the attraction between solute and water molecule is less.

Step-by-step solution

Understanding polar & non-polar substances

Polar substances or molecules possess regions of positive and negative charge. For example, water, sodium chloride, etc.

Non-polar substances or molecules have no separation of charge, so there are no positive or negative poles are formed. For example, benzene, methane, etc.

Solubility

A substance's solubility depends on the solvent's nature and concentration.If the interaction of the solute particles with the solvent is greater, then the substance is said to be more soluble or strongly soluble.

Solubility of polar substances in water

Water is a "universal solvent," but this statement is partially true because most substances are water soluble, but some are insoluble in water.

The polar and ionic substances are easily dissolved in water because of their polar characteristics. If the solute is polar, then it attracts the water molecule through hydrogen bonding. The ions of polar substances are easily separated due to the water molecule's higher dielectric constant, weakening the attractive forces between oppositely charged ions.

Solubility of non-polar substances in water

The non-polar substances neither possess the partial positive nor partial negative region. Therefore the attraction between non-polar substances and water molecules is less. Hence they cannot dissolve in water.