{"id":1556,"date":"2018-03-21T15:26:02","date_gmt":"2018-03-21T15:26:02","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-orgbiochemistry\/chapter\/physical-properties-of-carboxylic-acids\/"},"modified":"2018-11-07T21:19:35","modified_gmt":"2018-11-07T21:19:35","slug":"physical-properties-of-carboxylic-acids","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroecc-orgbiochemistry\/chapter\/physical-properties-of-carboxylic-acids\/","title":{"raw":"15.4 Physical Properties of Carboxylic Acids","rendered":"15.4 Physical Properties of Carboxylic Acids"},"content":{"raw":"
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Learning Objectives<\/h3>\r\n
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  1. Compare the boiling points of carboxylic acids with alcohols of similar molar mass.<\/li>\r\n \t
  2. Compare the solubilities of carboxylic acids in water with the solubilities of comparable alkanes and alcohols in water.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

    Many carboxylic acids are colorless liquids with disagreeable odors. The carboxylic acids with 5 to 10 carbon atoms all have \u201cgoaty\u201d odors (explaining the odor of Limburger cheese). These acids are also produced by the action of skin bacteria on human sebum (skin oils), which accounts for the odor of poorly ventilated locker rooms. The acids with more than 10 carbon atoms are waxlike solids, and their odor diminishes with increasing molar mass and resultant decreasing volatility.<\/p>\r\n

    Carboxylic acids exhibit strong hydrogen bonding between molecules, forming dimers in the gas phase, as shown below. \u00a0 They therefore have high boiling points compared to other substances of comparable molar mass: the entity that actually enters the gas phase, carboxylic acid dimer, is actually twice as large as the carboxylic acid molecule!<\/p>\r\n\r\n\r\n[caption id=\"attachment_3532\" align=\"aligncenter\" width=\"300\"]\"\" Carboxylic Acid dimer, public domain image[\/caption]\r\n

    The carboxyl group readily engages in hydrogen bonding with water molecules (Figure 15.3 \"Hydrogen Bonding between an Acetic Acid Molecule and Water Molecules\"<\/a>). The acids with one to four carbon atoms are completely miscible with water. Solubility decreases as the carbon chain length increases because dipole forces become less important and dispersion forces become more predominant. Hexanoic acid [CH3<\/sub>(CH2<\/sub>)4<\/sub>COOH] is barely soluble in water (about 1.0 g\/100 g of water). Palmitic acid [CH3<\/sub>(CH2<\/sub>)14<\/sub>COOH], with its large nonpolar hydrocarbon component, is essentially insoluble in water. The larger carboxylic acids generally are soluble in such organic solvents as ethanol, toluene, and diethyl ether.<\/p>\r\n\r\n

    \r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1545\"]\"image\" Figure 15.3 Hydrogen Bonding between an Acetic Acid Molecule and Water Molecules.\u00a0Carboxylic acids of low molar mass are quite soluble in water.[\/caption]\r\n\r\n<\/div>\r\n \r\n

    Table 15.2 \"Physical Constants of Carboxylic Acids\"<\/a> lists some physical properties for selected carboxylic acids. The first six are homologs. Notice that the boiling points increase with increasing molar mass, but the melting points show no regular pattern.<\/p>\r\n\r\n

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    Table 15.2<\/span> Physical Constants of Carboxylic Acids<\/th>\r\n<\/tr>\r\n
    Condensed Structural Formula<\/th>\r\nName of Acid<\/th>\r\nMelting Point (\u00b0C)<\/th>\r\nBoiling Point (\u00b0C)<\/th>\r\nSolubility (g\/100 g of Water)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
    HCOOH<\/td>\r\nformic acid<\/td>\r\n8<\/td>\r\n100<\/td>\r\nmiscible<\/td>\r\n<\/tr>\r\n
    CH3<\/sub>COOH<\/td>\r\nacetic acid<\/td>\r\n17<\/td>\r\n118<\/td>\r\nmiscible<\/td>\r\n<\/tr>\r\n
    CH3<\/sub>CH2<\/sub>COOH<\/td>\r\npropionic acid<\/td>\r\n\u201322<\/td>\r\n141<\/td>\r\nmiscible<\/td>\r\n<\/tr>\r\n
    CH3<\/sub>(CH2<\/sub>)2<\/sub>COOH<\/td>\r\nbutyric acid<\/td>\r\n\u20135<\/td>\r\n163<\/td>\r\nmiscible<\/td>\r\n<\/tr>\r\n
    CH3<\/sub>(CH2<\/sub>)3<\/sub>COOH<\/td>\r\nvaleric acid<\/td>\r\n\u201335<\/td>\r\n187<\/td>\r\n5<\/td>\r\n<\/tr>\r\n
    CH3<\/sub>(CH2<\/sub>)4<\/sub>COOH<\/td>\r\ncaproic acid<\/td>\r\n\u20133<\/td>\r\n205<\/td>\r\n1.1<\/td>\r\n<\/tr>\r\n
    C6<\/sub>H5<\/sub>COOH<\/td>\r\nbenzoic acid<\/td>\r\n122<\/td>\r\n249<\/td>\r\n0.29<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/div>\r\n
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    Concept Review Exercises<\/h3>\r\n
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      Which compound has the higher boiling point\u2014butanoic acid (molar mass 88) or 2-pentanone (molar mass 86)? Explain.<\/p>\r\n\r\n<\/div><\/li>\r\n \t

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      Would you expect butyric acid (butanoic acid) to be more or less soluble than 1-butanol in water? Explain.<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n

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      [reveal-answer q=\"399027\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"399027\"]<\/p>\r\n\r\n

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      1. Butyric acidhas the higher boiling point\u00a0 because of hydrogen bonding, in particular the reciprocal hydrogen bonding that forms dimers.\u00a0 There is no intermolecular hydrogen bonding in 2-pentanone.<\/li>\r\n \t
      2. Butanoic acid is more soluble than 1-butanol because butanoic acid has more extensive hydrogen bonding. [\/hidden-answer]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
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        Key Takeaways<\/h3>\r\n<\/div>\r\n
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