[CHEM] Chapter 11.5 - Carboxylic Acids

1 DARRELL ER (COPYRIGHTED) © TOPIC 11.5: CARBOXYLIC ACIDS DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT MASTERY EXAM WEIGHTAGE • Key component of Organic Chemistry • Important build up to ‘Macromolecules’ • Know how to draw your –COOH functional group • Understand how esterification works and the conditions needed • Heavy overall weightage • Entire Organic Chemistry portion accounts for 15- 20% of each year’s Chemistry paper DARRELL ER (COPYRIGHTED) ©

3 CARBOXYLIC ACIDS HOMOLOGOUS SERIES FUNCTIONAL GROUP GENERAL FORMULA KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

4 CARBOXYLIC ACIDS Carboxylic acids have a general formula: CnH2n+1COOH. Functional group Carboxylic acids contain the -COOH functional group (carboxyl group). Isomerism Carboxylic acid molecules that contain at least four carbon atoms will display isomerism. Isomers have the same molecular formula and similar chemical properties. However, isomers have different physical properties such as different melting and boiling points and densities. DARRELL ER (COPYRIGHTED) © Name Carbon atoms Molecular Formula Full Structural Formula Condensed structural formula Methanoic acid 1 HCOOH HCOOH Ethanoic acid 2 CH3COOH CH3COOH Propanoic acid 3 C2H5COOH CH3CH2COOH Butanoic acid 4 C3H7COOH CH3 CH2CH2COOH

5 CARBOXYLIC ACIDS PHYSICAL PROPERTIES PRODUCTION OF ETHANOIC ACID ESTERIFICATION KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

6 PHYSICAL PROPERTIES DARRELL ER (COPYRIGHTED) © Physical property Reasoning Melting and boiling points As the number of carbon atoms in the carboxylic acids increases, the melting and boiling points of carboxylic acids increases as well. As the number of carbon atoms in a carboxylic acid increases, the size of the molecules are bigger and have stronger intermolecular forces of attraction between each other. As such, more heat energy is needed to overcome the intermolecular forces of attraction between the carboxylic acid molecules. Hence, larger carboxylic acid containing more carbon atoms will have higher melting and boiling points. Volatility As the number of carbon atoms in the carboxylic acid increases, the volatility of carboxylic acid decreases. (similar to m.p. & b.p.) With a higher relative molecular mass, there would be stronger intermolecular forces of attraction between the carboxylic acid molecules. As such, more heat energy is needed to overcome the intermolecular forces of attraction between the carboxylic acid molecules. Density As the number of carbon atoms in the carboxylic acid increases, the density of carboxylic acid increases. Viscosity As the number of carbon atoms in the carboxylic acid increases, the viscosity of carboxylic acid decreases. (more difficult to flow) Carboxylic acids with longer hydrocarbon chains flow less easily as they tend to get stuck toget