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What are carboxylic acids? • Carboxylic acids are compounds which contain a Carboxyl group. • The -COOH group is attached either to a hydrogen atom or to an alkyl group. Carboxylic acids Aliphatic Monocarboxylic Acid Aromatic Dicarboxylic Acid Polycarboxylic Acid Physical Properties • Boiling point The boiling points of carboxylic acids of similar size are higher than alcohols. The higher boiling points of the carboxylic acids are still caused by hydrogen bonding. In a pure carboxylic acid, hydrogen bonding can occur between two molecules of acid O H O C R R C O H O hydrogen bond between the fairly positive hydrogen atom and a lone pairon the fairly negative oxygen atom. There are 3 polar bonds: 1. C=O 2. C-O 3. O-H They cause reactivity high solubility in aqueous media • Carboxylic acid derivatives also contains a carboxyl group, but now there is an electronegative atom (oxygen, nitrogen, or a halogen) attached to the carboxyl carbon. This difference in structure leads to a major change in reactivity. Chemical Properties 1. Sodium Bicarbonate test (acidity test) General test for carboxylic acids O RCOH + NaHCO3 O RCO Na + H2O + CO2 bubbles Evolution of a carbon dioxide gas is a positive test for the presence of the carboxylic acid 2. Ferric Chloride test O RCOH + FeCl3 O (RCO)3Fe + 3NH3 Ammonium chloride Red Coloration Oxalic acid + Ammonium Oxalate Lime Green Benzoic acid Tan 3. Calcium Chloride test Ammonium acetate Clear Di acid + Ammonium salts White ppt