{"id":856,"date":"2018-03-20T16:18:15","date_gmt":"2018-03-20T16:18:15","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-orgbiochemistry\/?post_type=chapter&p=856"},"modified":"2018-10-02T20:08:43","modified_gmt":"2018-10-02T20:08:43","slug":"10-2-bronsted-lowry-definition-of-acids-and-bases","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroecc-orgbiochemistry\/chapter\/10-2-bronsted-lowry-definition-of-acids-and-bases\/","title":{"raw":"10.2 Br\u00f8nsted-Lowry Definition of Acids and Bases","rendered":"10.2 Br\u00f8nsted-Lowry Definition of Acids and Bases"},"content":{"raw":"
\r\n
<\/div>\r\n<\/div>\r\n
\r\n
\r\n

10.2<\/span> Br\u00f8nsted-Lowry Definition of Acids and Bases<\/h2>\r\n
\r\n
\r\n

Learning Objectives<\/h3>\r\n
    \r\n \t
  1. Recognize a compound as a Br\u00f8nsted-Lowry acid or a Br\u00f8nsted-Lowry base.<\/li>\r\n \t
  2. Illustrate the proton transfer process that defines a Br\u00f8nsted-Lowry acid-base reaction.<\/li>\r\n \t
  3. Identify the following in a reaction equation: Br\u00f8nsted-Lowry: acid, base, conjugate acid, conjugate base<\/li>\r\n<\/ol>\r\n<\/div>\r\nBr\u00f8nsted-Lowry View of Reaction of a Base with Water<\/strong><\/span>\r\n\r\nAmmonia (NH<\/span>3<\/sub>) increases the hydroxide ion concentration in aqueous solution by reacting with water rather than releasing hydroxide ions directly. In fact, the Arrhenius definitions of an acid and a base focus on hydrogen ions and hydroxide ions. Are there more fundamental definitions for acids and bases?<\/span>\r\n\r\n<\/div>\r\n

    In 1923, the Danish scientist Johannes Br\u00f8nsted and the English scientist Thomas Lowry independently proposed new definitions for acids and bases. Rather than considering both hydrogen and hydroxide ions, they focused on the hydrogen ion only. A Br\u00f8nsted-Lowry acid<\/span><\/span>\u00a0is a compound that supplies a hydrogen ion in a reaction<\/strong>. A Br\u00f8nsted-Lowry base<\/span><\/span>, conversely, is a compound that accepts a hydrogen ion in a reaction.<\/strong> Thus, the Br\u00f8nsted-Lowry definitions of an acid and a base focus on the movement of hydrogen ions in a reaction, rather than on the production of hydrogen ions and hydroxide ions in an aqueous solution.\u00a0 Reactions that involve weak acids and bases are also reversible, indicated by the double arrow, and the chemical that acts as the acid in the reverse reaction is identified as the conjugate acid<\/strong>, while the chemical that acts as the base in the reverse reaction is the conjugate base<\/strong>.<\/p>\r\n

    The reaction of ammonia in water demonstrates the Br\u00f8nsted-Lowry definitions of acid, base, conjugate acid, and conjugate base. Ammonia and water molecules are reactants, while the ammonium ion and the hydroxide ion are products:<\/p>\r\n

    NH3<\/sub>(aq) + H2<\/sub>O(\u2113) \u2192 NH4<\/sub>+<\/sup>(aq) + OH\u2212<\/sup>(aq)<\/span><\/span><\/p>\r\n

    What has happened in this reaction is that the original water molecule has donated a hydrogen ion to the original ammonia molecule, which in turn has accepted the hydrogen ion. We can illustrate this as follows:<\/p>\r\n\"\"\r\n

    Because the water molecule donates a hydrogen ion to the ammonia, it is the Br\u00f8nsted-Lowry acid, while the ammonia molecule\u2014which accepts the hydrogen ion\u2014is the Br\u00f8nsted-Lowry base. Thus, ammonia acts as a base in both the Arrhenius sense and the Br\u00f8nsted-Lowry sense.<\/p>\r\n \r\n

    Br\u00f8nsted-Lowry View of Reaction of an Acid with Water<\/strong><\/p>\r\n

    Understanding how an Arrhenius acid like hydrochloric acid is still an acid in the Br\u00f8nsted-Lowry sense requires understanding what really happens when HCl dissolves in water. Recall that the hydrogen atom<\/em> is a single proton surrounded by a single electron. The hydrogen ion <\/em>is formed by removing the electron, leaving a bare proton. Are there really bare protons floating around in aqueous solution?\u00a0 No. What really happens is that the H+<\/sup> ion attaches itself to H2<\/sub>O to make H3<\/sub>O+<\/sup>, which is called the hydronium ion<\/em>. For most purposes, H+<\/sup> and H3<\/sub>O+<\/sup> represent the same species, but writing H3<\/sub>O+<\/sup> instead of H+<\/sup> recognizes that there are no bare protons floating around in solution. Rather, these protons are actually attached to solvent molecules<\/p>\r\n

    With this in mind, how is HCl defined as an acid in the Br\u00f8nsted-Lowry sense? Consider what happens when HCl dissolves in H2<\/sub>O:<\/p>\r\n

    HCl + H2<\/sub>O(\u2113) \u2192 H3<\/sub>O+<\/sup>(aq) + Cl\u2212<\/sup>(aq)<\/span><\/span><\/p>\r\n

    HCl is a strong electrolyte\/strong acid, so there is no reverse arrow.\u00a0 Lewis electron dot diagrams show the movement of a proton:<\/p>\r\n\r\n

    \"image\"<\/div>\r\n

    Now we see that a hydrogen ion is transferred from the HCl molecule to the H2<\/sub>O molecule to make chloride ions and hydronium ions. As the hydrogen ion donor, HCl acts as a Br\u00f8nsted-Lowry acid; as a hydrogen ion acceptor, H2<\/sub>O is a Br\u00f8nsted-Lowry base. So HCl is an acid not just in the Arrhenius sense but also in the Br\u00f8nsted-Lowry sense. Moreover, by the Br\u00f8nsted-Lowry definitions, H2<\/sub>O is a base in the formation of aqueous HCl. So the Br\u00f8nsted-Lowry definitions of an acid and a base classify the dissolving of HCl in water as a reaction between an acid and a base\u2014although the Arrhenius definition would not have labeled H2<\/sub>O a base in this circumstance.<\/p>\r\n\r\n

    \r\n
    \r\n

    Note<\/h3>\r\n

    In the Br\u00f8nsted-Lowry sense, water can act as an acid or a base based on its actions in a particular reaction.\u00a0 <\/em>The H+<\/sup> ion always acts as an acid or a conjugate acid.\u00a0 The OH-<\/sup> ion always acts as a base or conjugate base.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n

    \r\n

    Example 3<\/h3>\r\n

    Aniline (C6<\/sub>H5<\/sub>NH2<\/sub>) is slightly soluble in water. It has a nitrogen atom that can accept a hydrogen ion from a water molecule just like the nitrogen atom in ammonia does. Write the chemical equation for this reaction and identify the Br\u00f8nsted-Lowry acid and base.<\/p>\r\n

    Solution<\/p>\r\n

    C6<\/sub>H5<\/sub>NH2<\/sub> and H2<\/sub>O are the reactants. When C6<\/sub>H5<\/sub>NH2<\/sub> accepts a proton from H2<\/sub>O, it gains an extra H and a positive charge and leaves an OH\u2212<\/sup> ion behind. The reaction is as follows:<\/p>\r\n

    C6<\/sub>H5<\/sub>NH2<\/sub>(aq) + H2<\/sub>O(\u2113) \u21c6 C6<\/sub>H5<\/sub>NH3<\/sub>+<\/sup>(aq) + OH\u2212<\/sup>(aq)<\/span><\/span><\/p>\r\n

    Because C6<\/sub>H5<\/sub>NH2<\/sub> accepts a proton, it is the Br\u00f8nsted-Lowry base. The H2<\/sub>O molecule, because it donates a proton, is the Br\u00f8nsted-Lowry acid.\u00a0 In the reverse reaction, C6<\/sub>H5<\/sub>NH3<\/sub>+<\/sup> donates an H+<\/sup>, so it is the conjugate acid.\u00a0 In the reverse reaction, OH\u2212<\/sup> accepts an H+<\/sup>, so it is the conjugate base.<\/span><\/span><\/p>\r\n\r\n<\/div>\r\n

    \r\n
    \r\n

    Skill-Building Exercise<\/h3>\r\n
      \r\n \t
    1. \r\n
      \r\n

      Caffeine (C8<\/sub>H10<\/sub>N4<\/sub>O2<\/sub>) is a stimulant found in coffees and teas. When dissolved in water, it can accept a proton from a water molecule. Write the chemical equation for this process and identify the Br\u00f8nsted-Lowry acid, base, conjugate acid, and conjugate base.<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

      \r\n
      \r\n

      To Your Health: Br\u00f8nsted-Lowry Acid-Base Reactions in Pharmaceuticals<\/h3>\r\n

      There are many interesting applications of Br\u00f8nsted-Lowry acid-base reactions in the pharmaceutical industry. For example, drugs often need to be water soluble for maximum effectiveness. However, many complex organic compounds are not soluble or are only slightly soluble in water. Fortunately, those drugs that contain proton-accepting nitrogen atoms (and there are a lot of them) can be reacted with dilute hydrochloric acid [HCl(aq)]. The nitrogen atoms\u2014acting as Br\u00f8nsted-Lowry bases\u2014accept the hydrogen ions from the acid to make an ion, which is usually much more soluble in water. The modified drug molecules can then be isolated as chloride salts:<\/p>\r\n

      RN(sl\u00a0aq)\u00a0+\u00a0H+(aq)\u00a0\u2192\u00a0RNH+(aq)\u00a0\u2192Cl\u2212(aq)\u00a0RNHCl(s) <\/span><\/p>\r\n

      where RN represents some organic compound containing nitrogen. The label (sl aq)<\/em> means \u201cslightly aqueous,\u201d indicating that the compound RN is only slightly soluble. Drugs that are modified in this way are called hydrochloride salts<\/em>. Examples include the powerful painkiller codeine, which is commonly administered as codeine hydrochloride. Acids other than hydrochloric acid are also used. Hydrobromic acid, for example, gives hydrobromide salts<\/em>. Dextromethorphan, an ingredient in many cough medicines, is dispensed as dextromethorphan hydrobromide.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n

      \r\n
      \r\n

      Concept Review Exercise<\/h3>\r\n
        \r\n \t
      1. \r\n
        \r\n

        Give the definitions of a Br\u00f8nsted-Lowry acid and a Br\u00f8nsted-Lowry base.<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n

        \r\n

        Answer<\/h3>\r\n
        \r\n
          \r\n \t
        1. \r\n
          \r\n

          A Br\u00f8nsted-Lowry acid is a proton donor, while a Br\u00f8nsted-Lowry base is a proton acceptor.<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n

          \r\n
          \r\n

          Key Takeaways<\/h3>\r\n
            \r\n \t
          • A Br\u00f8nsted-Lowry acid is a proton donor, and a Br\u00f8nsted-Lowry base is a proton acceptor.<\/li>\r\n \t
          • A Br\u00f8nsted-Lowry conjugate acid is a proton donor in the reverse reaction, and a Br\u00f8nsted-Lowry conjugate base is a proton acceptor in the reverse reaction.<\/li>\r\n \t
          • Br\u00f8nsted-Lowry acid-base reactions are essentially proton transfer reactions.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
            \r\n
            \r\n
            \r\n

            Exercises<\/h3>\r\n
              \r\n \t
            1. \r\n
              \r\n

              Label each chemical as a Br\u00f8nsted-Lowry acid, base, conjugate acid, or conjugate base.<\/p>\r\n

              HCl(aq) + NH3<\/sub>(aq) \u2192 NH4<\/sub>+<\/sup>(aq) + Cl\u2212<\/sup>(aq)<\/span><\/span><\/p>\r\n\r\n<\/div><\/li>\r\n \t

            2. \r\n
              \r\n

              Label each chemical as a Br\u00f8nsted-Lowry acid, base, conjugate acid, or conjugate base<\/p>\r\n

              H2<\/sub>O(\u2113) + N2<\/sub>H4<\/sub>(aq) \u21c6 N2<\/sub>H5<\/sub>+<\/sup>(aq) + OH\u2212<\/sup>(aq)<\/span><\/span><\/p>\r\n\r\n<\/div><\/li>\r\n \t

            3. \r\n
              \r\n

              Explain why a Br\u00f8nsted-Lowry acid can be called a proton donor.<\/p>\r\n\r\n<\/div><\/li>\r\n \t

            4. \r\n
              \r\n

              Explain why a Br\u00f8nsted-Lowry base can be called a proton acceptor.<\/p>\r\n\r\n<\/div><\/li>\r\n \t

            5. \r\n
              \r\n

              Write the chemical equation of the reaction of ammonia in water and label the acid, base, conjugate acid, and conjugate base.<\/p>\r\n\r\n<\/div><\/li>\r\n \t

            6. \r\n
              \r\n

              Write the chemical equation of the reaction of methylamine (CH3<\/sub>NH2<\/sub>) in water and label the acid, base, conjugate acid, and conjugate base.<\/p>\r\n\r\n<\/div><\/li>\r\n \t

            7. \r\n
              \r\n

              Demonstrate that the dissolution of HNO3<\/sub> in water is actually a Br\u00f8nsted-Lowry acid-base reaction by describing it with a chemical equation and labeling the Br\u00f8nsted-Lowry acid and base.<\/p>\r\n\r\n<\/div><\/li>\r\n \t

            8. \r\n
              \r\n

              Identify the acid, base, conjugate acid, and conjugate base in the following chemical equation:<\/p>\r\n

              C3<\/sub>H7<\/sub>NH2<\/sub>(aq) + H3<\/sub>O+<\/sup>(aq) \u21c6 C3<\/sub>H7<\/sub>NH3<\/sub>+<\/sup>(aq) + H2<\/sub>O(\u2113)<\/span><\/span><\/p>\r\n\r\n<\/div><\/li>\r\n \t

            9. \r\n
              \r\n

              Write the chemical equation for the reaction that occurs when cocaine hydrochloride (C17<\/sub>H22<\/sub>ClNO4<\/sub>) dissolves in water and donates a proton to a water molecule. (When hydrochlorides dissolve in water, they separate into chloride ions and the appropriate cation.)<\/p>\r\n\r\n<\/div><\/li>\r\n \t

            10. \r\n
              \r\n

              If codeine hydrobromide has the formula C18<\/sub>H22<\/sub>BrNO3<\/sub>, what is the formula of the parent compound codeine?<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

              \r\n
              \r\n
              \r\n
              \r\n

              Answers<\/h3>\r\n<\/div>\r\n
              \r\n
              \r\n

              1. HCl: Br\u00f8nsted-Lowry acid; NH3<\/sub>: Br\u00f8nsted-Lowry base; NH4<\/sub>+<\/sup> conjugate acid; Cl-<\/sup> conjugate base<\/p>\r\n\r\n<\/div>\r\n

              <\/div>\r\n
              \r\n

              3. A Br\u00f8nsted-Lowry acid gives away an H+<\/sup> ion\u2014nominally, a proton\u2014in an acid-base reaction.<\/p>\r\n\r\n<\/div>\r\n

              <\/div>\r\n
              \r\n

              5. NH3<\/sub> + H2<\/sub>O \u21c6 NH4<\/sub>+<\/sup> + OH\u2212<\/sup>; NH3<\/sub>: Br\u00f8nsted-Lowry base; H2<\/sub>O: Br\u00f8nsted-Lowry acid; NH4<\/sub>+<\/sup> conjugate acid; OH-<\/sup> conjugate base<\/p>\r\n\r\n<\/div>\r\n

              <\/div>\r\n
              \r\n

              7. HNO3<\/sub> + H2<\/sub>O \u2192 H3<\/sub>O+<\/sup> + NO3<\/sub>\u2212<\/sup>; HNO3<\/sub>: Br\u00f8nsted-Lowry acid; H2<\/sub>O: Br\u00f8nsted-Lowry base; H3<\/sub>O+<\/sup> conjugate acid; OH-<\/sup> conjugate base<\/p>\r\n\r\n<\/div>\r\n

              <\/div>\r\n
              \r\n

              9. C17<\/sub>H22<\/sub>NO4+<\/sub> + H2<\/sub>O \u21c6 H3<\/sub>O+<\/sup> + C17<\/sub>H21<\/sub>NO4<\/sub><\/p>\r\n\r\n<\/div>\r\n

              <\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
              <\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"
              \n
              <\/div>\n<\/div>\n
              \n
              \n

              10.2<\/span> Br\u00f8nsted-Lowry Definition of Acids and Bases<\/h2>\n
              \n
              \n

              Learning Objectives<\/h3>\n
                \n
              1. Recognize a compound as a Br\u00f8nsted-Lowry acid or a Br\u00f8nsted-Lowry base.<\/li>\n
              2. Illustrate the proton transfer process that defines a Br\u00f8nsted-Lowry acid-base reaction.<\/li>\n
              3. Identify the following in a reaction equation: Br\u00f8nsted-Lowry: acid, base, conjugate acid, conjugate base<\/li>\n<\/ol>\n<\/div>\n

                Br\u00f8nsted-Lowry View of Reaction of a Base with Water<\/strong><\/span><\/p>\n

                Ammonia (NH<\/span>3<\/sub>) increases the hydroxide ion concentration in aqueous solution by reacting with water rather than releasing hydroxide ions directly. In fact, the Arrhenius definitions of an acid and a base focus on hydrogen ions and hydroxide ions. Are there more fundamental definitions for acids and bases?<\/span><\/p>\n<\/div>\n

                In 1923, the Danish scientist Johannes Br\u00f8nsted and the English scientist Thomas Lowry independently proposed new definitions for acids and bases. Rather than considering both hydrogen and hydroxide ions, they focused on the hydrogen ion only. A Br\u00f8nsted-Lowry acid<\/span><\/span>\u00a0is a compound that supplies a hydrogen ion in a reaction<\/strong>. A Br\u00f8nsted-Lowry base<\/span><\/span>, conversely, is a compound that accepts a hydrogen ion in a reaction.<\/strong> Thus, the Br\u00f8nsted-Lowry definitions of an acid and a base focus on the movement of hydrogen ions in a reaction, rather than on the production of hydrogen ions and hydroxide ions in an aqueous solution.\u00a0 Reactions that involve weak acids and bases are also reversible, indicated by the double arrow, and the chemical that acts as the acid in the reverse reaction is identified as the conjugate acid<\/strong>, while the chemical that acts as the base in the reverse reaction is the conjugate base<\/strong>.<\/p>\n

                The reaction of ammonia in water demonstrates the Br\u00f8nsted-Lowry definitions of acid, base, conjugate acid, and conjugate base. Ammonia and water molecules are reactants, while the ammonium ion and the hydroxide ion are products:<\/p>\n

                NH3<\/sub>(aq) + H2<\/sub>O(\u2113) \u2192 NH4<\/sub>+<\/sup>(aq) + OH\u2212<\/sup>(aq)<\/span><\/span><\/p>\n

                What has happened in this reaction is that the original water molecule has donated a hydrogen ion to the original ammonia molecule, which in turn has accepted the hydrogen ion. We can illustrate this as follows:<\/p>\n

                \"\"<\/p>\n

                Because the water molecule donates a hydrogen ion to the ammonia, it is the Br\u00f8nsted-Lowry acid, while the ammonia molecule\u2014which accepts the hydrogen ion\u2014is the Br\u00f8nsted-Lowry base. Thus, ammonia acts as a base in both the Arrhenius sense and the Br\u00f8nsted-Lowry sense.<\/p>\n

                 <\/p>\n

                Br\u00f8nsted-Lowry View of Reaction of an Acid with Water<\/strong><\/p>\n

                Understanding how an Arrhenius acid like hydrochloric acid is still an acid in the Br\u00f8nsted-Lowry sense requires understanding what really happens when HCl dissolves in water. Recall that the hydrogen atom<\/em> is a single proton surrounded by a single electron. The hydrogen ion <\/em>is formed by removing the electron, leaving a bare proton. Are there really bare protons floating around in aqueous solution?\u00a0 No. What really happens is that the H+<\/sup> ion attaches itself to H2<\/sub>O to make H3<\/sub>O+<\/sup>, which is called the hydronium ion<\/em>. For most purposes, H+<\/sup> and H3<\/sub>O+<\/sup> represent the same species, but writing H3<\/sub>O+<\/sup> instead of H+<\/sup> recognizes that there are no bare protons floating around in solution. Rather, these protons are actually attached to solvent molecules<\/p>\n

                With this in mind, how is HCl defined as an acid in the Br\u00f8nsted-Lowry sense? Consider what happens when HCl dissolves in H2<\/sub>O:<\/p>\n

                HCl + H2<\/sub>O(\u2113) \u2192 H3<\/sub>O+<\/sup>(aq) + Cl\u2212<\/sup>(aq)<\/span><\/span><\/p>\n

                HCl is a strong electrolyte\/strong acid, so there is no reverse arrow.\u00a0 Lewis electron dot diagrams show the movement of a proton:<\/p>\n

                \"image\"<\/div>\n

                Now we see that a hydrogen ion is transferred from the HCl molecule to the H2<\/sub>O molecule to make chloride ions and hydronium ions. As the hydrogen ion donor, HCl acts as a Br\u00f8nsted-Lowry acid; as a hydrogen ion acceptor, H2<\/sub>O is a Br\u00f8nsted-Lowry base. So HCl is an acid not just in the Arrhenius sense but also in the Br\u00f8nsted-Lowry sense. Moreover, by the Br\u00f8nsted-Lowry definitions, H2<\/sub>O is a base in the formation of aqueous HCl. So the Br\u00f8nsted-Lowry definitions of an acid and a base classify the dissolving of HCl in water as a reaction between an acid and a base\u2014although the Arrhenius definition would not have labeled H2<\/sub>O a base in this circumstance.<\/p>\n

                \n
                \n

                Note<\/h3>\n

                In the Br\u00f8nsted-Lowry sense, water can act as an acid or a base based on its actions in a particular reaction.\u00a0 <\/em>The H+<\/sup> ion always acts as an acid or a conjugate acid.\u00a0 The OH–<\/sup> ion always acts as a base or conjugate base.<\/p>\n<\/div>\n<\/div>\n

                \n

                Example 3<\/h3>\n

                Aniline (C6<\/sub>H5<\/sub>NH2<\/sub>) is slightly soluble in water. It has a nitrogen atom that can accept a hydrogen ion from a water molecule just like the nitrogen atom in ammonia does. Write the chemical equation for this reaction and identify the Br\u00f8nsted-Lowry acid and base.<\/p>\n

                Solution<\/p>\n

                C6<\/sub>H5<\/sub>NH2<\/sub> and H2<\/sub>O are the reactants. When C6<\/sub>H5<\/sub>NH2<\/sub> accepts a proton from H2<\/sub>O, it gains an extra H and a positive charge and leaves an OH\u2212<\/sup> ion behind. The reaction is as follows:<\/p>\n

                C6<\/sub>H5<\/sub>NH2<\/sub>(aq) + H2<\/sub>O(\u2113) \u21c6 C6<\/sub>H5<\/sub>NH3<\/sub>+<\/sup>(aq) + OH\u2212<\/sup>(aq)<\/span><\/span><\/p>\n

                Because C6<\/sub>H5<\/sub>NH2<\/sub> accepts a proton, it is the Br\u00f8nsted-Lowry base. The H2<\/sub>O molecule, because it donates a proton, is the Br\u00f8nsted-Lowry acid.\u00a0 In the reverse reaction, C6<\/sub>H5<\/sub>NH3<\/sub>+<\/sup> donates an H+<\/sup>, so it is the conjugate acid.\u00a0 In the reverse reaction, OH\u2212<\/sup> accepts an H+<\/sup>, so it is the conjugate base.<\/span><\/span><\/p>\n<\/div>\n

                \n
                \n

                Skill-Building Exercise<\/h3>\n
                  \n
                1. \n
                  \n

                  Caffeine (C8<\/sub>H10<\/sub>N4<\/sub>O2<\/sub>) is a stimulant found in coffees and teas. When dissolved in water, it can accept a proton from a water molecule. Write the chemical equation for this process and identify the Br\u00f8nsted-Lowry acid, base, conjugate acid, and conjugate base.<\/p>\n<\/div>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n

                  \n
                  \n

                  To Your Health: Br\u00f8nsted-Lowry Acid-Base Reactions in Pharmaceuticals<\/h3>\n

                  There are many interesting applications of Br\u00f8nsted-Lowry acid-base reactions in the pharmaceutical industry. For example, drugs often need to be water soluble for maximum effectiveness. However, many complex organic compounds are not soluble or are only slightly soluble in water. Fortunately, those drugs that contain proton-accepting nitrogen atoms (and there are a lot of them) can be reacted with dilute hydrochloric acid [HCl(aq)]. The nitrogen atoms\u2014acting as Br\u00f8nsted-Lowry bases\u2014accept the hydrogen ions from the acid to make an ion, which is usually much more soluble in water. The modified drug molecules can then be isolated as chloride salts:<\/p>\n

                  RN(sl\u00a0aq)\u00a0+\u00a0H+(aq)\u00a0\u2192\u00a0RNH+(aq)\u00a0\u2192Cl\u2212(aq)\u00a0RNHCl(s) <\/span><\/p>\n

                  where RN represents some organic compound containing nitrogen. The label (sl aq)<\/em> means \u201cslightly aqueous,\u201d indicating that the compound RN is only slightly soluble. Drugs that are modified in this way are called hydrochloride salts<\/em>. Examples include the powerful painkiller codeine, which is commonly administered as codeine hydrochloride. Acids other than hydrochloric acid are also used. Hydrobromic acid, for example, gives hydrobromide salts<\/em>. Dextromethorphan, an ingredient in many cough medicines, is dispensed as dextromethorphan hydrobromide.<\/p>\n<\/div>\n<\/div>\n

                  \n
                  \n

                  Concept Review Exercise<\/h3>\n
                    \n
                  1. \n
                    \n

                    Give the definitions of a Br\u00f8nsted-Lowry acid and a Br\u00f8nsted-Lowry base.<\/p>\n<\/div>\n<\/li>\n<\/ol>\n<\/div>\n

                    \n

                    Answer<\/h3>\n
                    \n
                      \n
                    1. \n
                      \n

                      A Br\u00f8nsted-Lowry acid is a proton donor, while a Br\u00f8nsted-Lowry base is a proton acceptor.<\/p>\n<\/div>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n

                      \n
                      \n

                      Key Takeaways<\/h3>\n