When boiled with concentrated aqueous alkali, fats and oils dissolve, but waxes do not. Explain the difference.

To explain the difference between the behavior of fats and oils versus waxes when boiled with concentrated aqueous alkali, it is important to understand their chemical structures.

Fats and oils, both known as triglycerides, are composed of glycerol molecules bonded to three fatty acid chains. Fatty acids are long hydrocarbon chains with a carboxyl group at one end. The presence of these carboxyl groups makes fats and oils acidic in nature. When boiled with concentrated aqueous alkali (such as sodium hydroxide), a process called saponification occurs.

During saponification, the alkali breaks the ester bonds between the glycerol and the fatty acid chains, resulting in the formation of soap molecules. The hydroxide ions of the alkali react with the carboxyl groups of the fatty acids to form water and soap.

Waxes, on the other hand, have a different chemical structure compared to fats and oils. Waxes are esters formed by the combination of long-chain fatty acids with long-chain alcohols. Unlike fats and oils, waxes do not have a carboxyl group, which means they are not acidic in nature. Therefore, waxes do not undergo saponification when boiled with concentrated aqueous alkali.

Instead, when waxes are boiled with alkali, they may form emulsions or suspensions due to the mechanical disruption caused by the alkali's agitation. However, since waxes are nonpolar compounds, they generally do not dissolve in water or aqueous solutions.

In summary, the difference in behavior when boiled with concentrated aqueous alkali lies in the chemical structures of fats and oils versus waxes. Fats and oils contain acidic carboxyl groups and undergo saponification, while waxes lack carboxyl groups and do not saponify.