Q12.68P - Chemistry: Molecular Nature Of Matter And Change

Question

For what types of substances are water a good solvent? For what types is it a poor solvent? Explain.

Step-by-Step Solution

Answer

Polar compounds respond well to water as a solvent. For non-polar substances, water is a poor solvent. This is because of the strong-strong interactions for the like molecules i.e., polar-polar interactions between the polar molecules and dispersion forces between the non-polar molecules.

Polar and non-polar compounds

Compounds that have the polar functional group present like, $\mathbf{-}\mathbf{OH}\mathbf{,}\mathbf{-}{\mathbf{NH}}_2$ , etc. are polar compounds that have some electronegativity difference between the bonded atoms. Non-polar compounds do not have such electronegativity differences and are bonded to each other by sharing of electrons.

Like dissolves like formula

The polar compounds due to more interaction with polar solvents such as dipolar interactions, H-bonding, etc. dissolves in polar solvents like water.

Non-polar compounds do not have such strong intermolecular interactions thus weak London dispersion forces are in the picture. Hence, the non-polar compounds strongly interact with their counterparts i.e. non-polar solvents like hexane.

Water is good for polar compounds

Thus, due to the above interactions, polar water is a better solvent for polar compounds and a poor solvent for non-polar compounds.