[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 together. Flammability As the number of carbon atoms in the carboxylic acid increases, the flammability of alcohols decreases. (more difficult to burn) Solubility Carboxylic acids are soluble in water, but as the number of carbon atoms increases, solubility in water decreases.

7 PRODUCTION OF CARBOXYLIC ACID 1) Oxidation of alcohol Ethanol C2H5OH can be converted to ethanoic acid C2H5COOH using oxidising agents. C2H5OH (aq) + O2 (g)  CH3COOH (aq) + H2O (l) * MAKING ETHANOIC ACID DARRELL ER (COPYRIGHTED) © PRODUCTION OF ETHANOIC ACID 1) Oxidation of alcohol

8 NAME OF SALT FORMED Carboxylic acids are weak acids and will be able to react with reactive metals, bases and carbonates. The name of the salt formed would be based on the carboxylic acid that is used and ends with ‘-ate’. WEAK ACID DARRELL ER (COPYRIGHTED) © Carboxylic acids are weak acids as they only partially dissociate in water to release a low concentration of H+ ions. CH3COOH (aq) ⇌ CH3COO- (aq) + H+ (aq) Reaction Products formed Potassium hydroxide + propanoic acid (base + acid) Potassium propanoate + water (salt + water) Calcium Carbonate + pentanoic acid (carbonate + acid) Calcium pentanoate + carbon dioxide gas (salt + CO2) Magnesium + ethanoic acid (metal + acid) Magnesium ethanoate + hydrogen gas (salt + hydrogen gas)

9 CARBOXYLIC ACID & ALCOHOL REACTION (ESTERIFICATION) Carboxylic acids and alcohols can react to form esters. carboxylic acid + alcohol ⇌ ester + water (sulfuric acid & warming) The first half of the ester’s name comes from the alcohol. The second half of the ester’s name comes from the carboxylic acid and ends with ‘-oate’. CHEMICAL REACTIONS DARRELL ER (COPYRIGHTED) © CHEMICAL REACTIONS OF CARBOXYLIC ACIDS 1) Esterification Real-life applications for esters - Used as artificial fruity flavourings to soft drinks and ice creams. - Used as solvents for organic compounds - Used as as solvents for glues and perfumes Organic compounds used to form the ester Alcohol Acid Name of ester Ethanol Propanoic acid Ethyl propanoate Propanol Butanoic acid Propyl butanoate

ALL ORGANIC COMPOUNDS Complete Combustion Incomplete Combustion ALKANE ALKENE ALCOHOL CARBOXYLIC ACID C - C Prefix Meth- 1 Eth- 2 Prop- 3 But- 4 Pent- 5 Hex- 6 Hep- 7 Oct- 8 Non- 9 Dec- 10 Catalytic Cracking (Al2O3 & SiO2, 600 °C) X + O2 (g) → CO2 (g) + 2H2O (l) CH4 (g) + Br2 (g) → CH3Br (g) + HBr (g) Substitution (UV light) Hydrogenation (200 °C & nickel) Bromination (Test for C=C bonds) Hydration (300 °C & 60 atm, Phosphoric(V) acid) LONG CHAIN ALKANE Addition Polymerisation (High temp & pressure) H2 gas (For Haber process) Fermentation (37°C, yeast & no O2) SUGAR C6H12O6 → 2 C2H5OH + 2 CO2 C = C -OH Oxidation (acidified aqueous potassium manganate(VII) / exposed to air) Esterification (warm, sulfuric acid) ESTER + H2O -COOH -COO- Condensation Polymerisation (elimination of water) C2H4 (g) + Br2 (aq) → C2H4Br2 (aq) DARRELL ER (COPYRIGHTED) © DARRELL ER (COPYRIGHTED) © X + O2 (g) → CO (g) + 2H2O (l) POLYMER O