The presence of the carboxyl (-COOH) functional group determines the unique physical and chemical properties of this family.

1. Physical Properties
   
   
   1. Boiling point
      
      

      Study the table below. The earlier section discussed how the boiling points of alcohols increase with size. Now, consider how boiling point increases within a homologous series of carboxylic acids. Study the last three columns of the table below.

      
      
      
      Fig. 1   Comparing  Boiling Points and Solubilities of Alcohols and Carboxylic Acids
      
      
      

      Methanoic acid has one carbon atom whereas pentanoic acid has five carbon atoms. In a pattern similar to the alcohols, the boiling point increases steadily as the size of the carboxylic acid increases. This trend is due to the fact that larger molecules possess a greater number of electrons and, therefore, display stronger London forces. The dipole-dipole forces and the hydrogen bonding remain approximately the same for all the acids shown.

      A carboxylic acid has a higher boiling point than does an alcohol with the same number of carbon atoms. This is partially due to the fact that the carboxyl group is more polar than the hydroxyl group is, resulting in stronger dipole-dipole forces.  Carboxylic acids also have more locations where hydrogen bonding can occur.
      
      

   2. Solubility
      
      

      As well as forming hydrogen bonds with each other, carboxylic acids can form hydrogen bonds with water molecules, which increases their solubility. In fact, carboxylic acids exhibit the same solubility pattern as alcohols do. The smaller carboxylic acids are the most soluble in water whereas the larger carboxylic acids are virtually insoluble. The more -CH2 groups added to the parent chain, the greater the non-polar part of the acid and the lower its solubility.

2. Chemical Properties
   

   
   The presence of the carboxyl group determines the chemical properties of this family. What reactions involve carboxylic acids? You will explore this question in Lesson 2.