{"id":359,"date":"2017-10-24T16:17:32","date_gmt":"2017-10-24T16:17:32","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/?post_type=chapter&#038;p=359"},"modified":"2018-09-28T19:53:51","modified_gmt":"2018-09-28T19:53:51","slug":"bronsted-lowry-acids-and-bases","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/chapter\/bronsted-lowry-acids-and-bases\/","title":{"raw":"Br\u00f8nsted-Lowry Acids and Bases","rendered":"Br\u00f8nsted-Lowry Acids and Bases"},"content":{"raw":"<div class=\"elm-header\">\r\n<div class=\"elm-header-custom\">\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Objectives<\/h3>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div id=\"skills\">\r\n\r\nAfter completing this section, you should be able to\r\n<ol>\r\n \t<li>state the Br\u00f8nsted-Lowry definition of an acid and a base.<\/li>\r\n \t<li>identify the Br\u00f8nsted-Lowry acid and base in a given acid-base reaction.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Terms<\/h3>\r\n<div class=\"elm-header\"><\/div>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div>\r\n\r\nMake certain that you can define, and use in context, the key terms below.\r\n<ul>\r\n \t<li>acid (Br\u00f8nsted-Lowry)<\/li>\r\n \t<li>base (Br\u00f8nsted-Lowry)<\/li>\r\n \t<li>conjugate acid<\/li>\r\n \t<li>conjugate base<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox\">\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div id=\"note\">\r\n<h3 class=\"boxtitle\">Study Notes<\/h3>\r\nYou should be familiar with the Br\u00f8nsted-Lowry concept of acidity and the differences between strong and weak acids. You may wish to review this topic before proceeding.\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n\r\nIn 1923, chemists Johannes Br\u00f8nsted and Martin Lowry independently developed definitions of acids and bases based on compounds abilities to either donate or accept protons (H<sup>+<\/sup> ions). Here, acids are defined as being able to donate protons in the form of hydrogen ions; whereas bases are defined as being able to accept protons.\u00a0This took the <a title=\"Physical Chemistry\/Acids and Bases\/Acid\/Arrhenius Concept of Acids and Bases\" href=\"\/Physical_Chemistry\/Acids_and_Bases\/Acid\/Arrhenius_Concept_of_Acids_and_Bases\" rel=\"internal\">Arrhenius<\/a> definition one step further as water is no longer required to be present in the solution for acid and base reactions to occur.\r\n<div>\r\n<div id=\"section_1\">\r\n<h3 class=\"editable\">Br\u00f8nsted-Lowery Definition<\/h3>\r\n<p class=\"paragraph\">J.N. Br\u00f8nsted and T.M. Lowry independently developed the theory of proton donors and proton acceptors in acid-base reactions, coincidentally in the same region and during the\u00a0same year. The Arrhenius theory where acids and bases are defined by whether the molecule contains hydrogen and hydroxide ion is too limiting. The main effect of the Br\u00f8nsted-Lowry definition is to identify the proton (H<sup>+<\/sup>) transfer occurring in the acid-base reaction. This is best illustrated in the following equation:<\/p>\r\n\r\n<div>HA+Z\u21ccA\u2212+HZ+<\/div>\r\n<table style=\"margin: auto;border-spacing: 2px\" border=\"1\" cellpadding=\"0\">\r\n<tbody>\r\n<tr style=\"height: 16.9062px\">\r\n<td style=\"height: 16.9062px;width: 33%\">\u00a0<strong>Acid<\/strong><\/td>\r\n<td style=\"height: 16.9062px;width: 33%\">\u00a0<strong>Base<\/strong><\/td>\r\n<td style=\"height: 16.9062px;width: 34%\"><\/td>\r\n<\/tr>\r\n<tr style=\"height: 28px\">\r\n<td style=\"height: 28px;width: 33%\">\u00a0<strong>Donates hydrogen ions<\/strong><\/td>\r\n<td style=\"height: 28px;width: 33%\">\u00a0<strong>Accepts hydrogen ions.<\/strong><\/td>\r\n<td style=\"height: 28px;width: 34%\"><\/td>\r\n<\/tr>\r\n<tr style=\"height: 28px\">\r\n<td style=\"height: 28px\">\u00a0HCl<sup>+<\/sup><\/td>\r\n<td style=\"height: 28px\">\u00a0HOH \u2192<\/td>\r\n<td style=\"height: 28px\">H<sub>3<\/sub>O<sup>+<\/sup> + Cl<sup>-<\/sup><\/td>\r\n<\/tr>\r\n<tr style=\"height: 16px\">\r\n<td style=\"height: 16px\">\u00a0 HOH<sup>+<\/sup><\/td>\r\n<td style=\"height: 16px\">\u00a0 NH<sub>3<\/sub>\u2192<\/td>\r\n<td style=\"height: 16px\">\u00a0NH<sub>4<\/sub><sup>+<\/sup> + OH<sup>-<\/sup><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nThe determination of a substance as a Br\u00f8nsted-Lowery acid or base can only be done by observing the reaction. In the case of the HOH it is a base in the first case and an acid in the second case.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04153952\/180bronsted.gif\" alt=\"180bronsted.gif\" width=\"283px\" height=\"298px\" \/>\r\n\r\nTo determine whether a substance is an acid or a base, count the hydrogens on each substance before and after the reaction. If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions). If the number of hydrogens has increased that substance is the base (accepts hydrogen ions). These definitions are normally applied to the reactants on the left. If the reaction is viewed in reverse a new acid and base can be identified. The substances on the right side of the equation are called conjugate acid and conjugate base compared to those on the left. Also note that the original acid turns in the conjugate base after the reaction is over.\r\n\r\n<\/div>\r\n<div id=\"section_2\">\r\n<h3 class=\"editable\">Acids are Proton Donors and Bases are Proton Acceptors<\/h3>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<p class=\"paragraph\">For a reaction to be in equilibrium a transfer of electrons needs to occur. The acid will give an electron away and the base will receive the electron. Acids and Bases that work together in this fashion are called a <em class=\"italic\">conjugate pair<\/em> made up of <em class=\"italic\">conjugate acids<\/em> and <em class=\"italic\">conjugate bases<\/em>.HA+Z\u21ccA\u2212+HZ+<\/p>\r\n<p class=\"paragraph\">A stands for an Acidic compound and Z stands for a Basic compound<\/p>\r\n\r\n<ul>\r\n \t<li class=\"paragraph\">A Donates H to form HZ<sup class=\"superscript\">+<\/sup>.<\/li>\r\n \t<li class=\"paragraph\">Z Accepts H from A which forms HZ<sup class=\"superscript\">+<\/sup><\/li>\r\n \t<li class=\"paragraph\">A<sup class=\"superscript\">-<\/sup> becomes conjugate base of HA and in the reverse reaction it accepts a H from HZ to recreate HA in order to remain in equilibrium<\/li>\r\n \t<li class=\"paragraph\">HZ<sup class=\"superscript\">+<\/sup> becomes a conjugate acid of Z and in the reverse reaction it donates a H to A<sup class=\"superscript\">-<\/sup> recreating Z in order to remain in equilibrium<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div>\r\n<div id=\"section_3\">\r\n<div class=\"textbox examples\">\r\n<h3>Examples<\/h3>\r\n<div>\r\n<div id=\"section_3\">\r\n<h3 class=\"editable\">Questions<\/h3>\r\n<div class=\"editIcon\"><\/div>\r\n<ol>\r\n \t<li>Why is HA\u00a0an Acid?<\/li>\r\n \t<li>Why is A<sup>-<\/sup>\u00a0a Base?<\/li>\r\n \t<li class=\"paragraph\">How can A<sup class=\"superscript\">-<\/sup> be a base when HA was and Acid?<\/li>\r\n \t<li class=\"paragraph\">How can HZ<sup class=\"superscript\">+<\/sup> be an acid when Z used to be a Base?<\/li>\r\n \t<li class=\"paragraph\"><strong class=\"bold\">Now that we understand the concept, let's look at an an example with actual compounds!<\/strong>\r\n<div>HCl+H2O\u21ccH3O++Cl\u00af<\/div><\/li>\r\n<\/ol>\r\n<ul>\r\n \t<li class=\"paragraph\">HCL is the acid because it is donating a proton to H<sub>2<\/sub>O<\/li>\r\n \t<li class=\"paragraph\">H<sub>2<\/sub>O is the base because H<sub>2<\/sub>O is accepting a proton from HCL<\/li>\r\n \t<li class=\"paragraph\">H<sub>3<\/sub>O<sup class=\"superscript\">+<\/sup> is the conjugate acid because it is donating an acid to CL turn into it's conjugate acid H<sub>2<\/sub>O<\/li>\r\n \t<li class=\"paragraph\">Cl\u00af is the conjugate base because it accepts an H from H<sub>3<\/sub>O to return to it's conjugate acid HCl<\/li>\r\n<\/ul>\r\n<p class=\"paragraph\">How can H<sub>2<\/sub>O be a base? I thought it was neutral?<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div id=\"section_4\">\r\n<h3 class=\"editable\">Answers<\/h3>\r\n[reveal-answer q=\"710341\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"710341\"]1. It has a proton that can be transferred\r\n\r\n2. It receives a proton from HA\r\n\r\n3. A- is a conjugate base because it is in need of a H in order to remain in equilibrium and return to HA\r\n\r\n4. HZ+ is a conjugate acid because it needs to donate or give away its proton in order to return to it's previous state of Z\r\n\r\n5. In the Br\u00f8nsted-Lowry Theory what makes a compound an element or a base is whether or not it donates or accepts protons. If the H2O was in a different problem and was instead donating an H rather than accepting an H it would be an acid![\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div id=\"section_5\">\r\n<h3 class=\"editable\">\u00a0Conjugate Acid\u2013Base Pairs<\/h3>\r\nWe discussed the concept of conjugate acid\u2013base pairs in Chapter 4, using the reaction of ammonia, the base, with water, the acid, as an example. In aqueous solutions, acids and bases can be defined in terms of the transfer of a proton from an acid to a base. Thus for every acidic species in an aqueous solution, there exists a species derived from the acid by the loss of a proton. These two species that differ by only a proton constitute a <a>conjugate acid\u2013base pair<\/a>. For example, in the reaction of\u00a0<em>HCl\u00a0<\/em>with water (Equation 16.1),\u00a0<em>HCl<\/em>\u00a0, the parent acid, donates a proton to a water molecule, the parent base, thereby forming <em>Cl<sup>-<\/sup><\/em>. Thus\u00a0<em>Cl<\/em>\u00a0and\u00a0<em>Cl<sup>-<\/sup><\/em>\u00a0constitute a conjugate acid\u2013base pair. By convention, we always write a conjugate acid\u2013base pair as the acid followed by its conjugate base. In the reverse reaction, the <em>Cl<\/em><sup>-<\/sup>\u00a0ion in solution acts as a base to accept a proton from\u00a0<em>H<sub>3<\/sub>O<sup>+<\/sup><\/em>, forming\u00a0<em>H<sub>2<\/sub>O<\/em>\u00a0and\u00a0<em>HCl.<\/em>\u00a0Thus <em>H<sub>3<\/sub>O<sup>+<\/sup><\/em>\u00a0and <em>H<sub>2<\/sub>O<\/em>\u00a0constitute a second conjugate acid\u2013base pair. In general, any acid\u2013base reaction must contain two conjugate acid\u2013base pairs, which in this case are\u00a0<em>HCl\/Cl<sup>-<\/sup><\/em>\u00a0and <em>H<sub>3<\/sub>O<sup>+<\/sup>\/H<sub>2<\/sub>O<\/em>.\r\n<blockquote><img class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04153955\/13307049a0af1fc2a8588ee638396963.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/13307049a0af1fc2a8588ee638396963.jpg\" width=\"528\" height=\"170\" \/>\r\n<p class=\"boxtitle\">Note<\/p>\r\nAll acid\u2013base reactions contain two conjugate acid\u2013base pairs.<\/blockquote>\r\nSimilarly, in the reaction of acetic acid with water, acetic acid donates a proton to water, which acts as the base. In the reverse reaction, <em>H<sub>3<\/sub>O<sup>+<\/sup><\/em>\u00a0is the acid that donates a proton to the acetate ion, which acts as the base. Once again, we have two conjugate acid\u2013base pairs: the parent acid and its conjugate base (<i>CH<sub>3<\/sub>CO<sub>2<\/sub>H\/CH<sub>3<\/sub>CO<sub>2<\/sub><sup>-<\/sup><\/i>) and the parent base and its conjugate acid (<em>H<sub>3<\/sub>O<sup>+<\/sup>\/H<sub>2<\/sub>O<\/em>).\r\n\r\n<img class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04153958\/0976fc4b1971263ab1f1bf651617f1a6.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/0976fc4b1971263ab1f1bf651617f1a6.jpg\" width=\"502\" height=\"165\" \/>\r\n\r\nIn the reaction of ammonia with water to give ammonium ions and hydroxide ions (Equation 16.3), ammonia acts as a base by accepting a proton from a water molecule, which in this case means that water is acting as an acid. In the reverse reaction, an ammonium ion acts as an acid by donating a proton to a hydroxide ion, and the hydroxide ion acts as a base. The conjugate acid\u2013base pairs for this reaction are <em>NH<sub>4<\/sub><sup>+<\/sup>\/NH<sub>3<\/sub><\/em>\u00a0and <em>H<sub>2<\/sub>O\/OH<sup>-<\/sup><\/em>. Some common conjugate acid\u2013base pairs are shown in Figure 2.7.1.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"550\"]<img class=\"internal\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04154001\/d74ff3bb2b8f11ddd4804cc71e8fcb32.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/d74ff3bb2b8f11ddd4804cc71e8fcb32.jpg\" width=\"550\" height=\"180\" \/> Figure 1.\u00a0The Relative Strengths of Some Common Conjugate Acid\u2013Base Pairs[\/caption]\r\n\r\n<\/div>\r\n<\/div>\r\n<img class=\"internal\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04154005\/eec51e5746bb3b13108029410ecf1f45.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/eec51e5746bb3b13108029410ecf1f45.jpg\" width=\"270\" height=\"620\" \/>\r\n\r\nThe strongest acids are at the bottom left, and the strongest bases are at the top right. The conjugate base of a strong acid is a very weak base, and, conversely, the conjugate acid of a strong base is a very weak acid.\r\n<div id=\"section_6\">\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<h3>Questions<\/h3>\r\n<ol>\r\n \t<li>Identify the Br\u00f8nsted-Lowry acids and bases in the reactions given below.\r\n<ol>\r\n \t<li>$\\ce{\\sf{CH3CH2O^- + H2O &lt;=&gt; CH3CH2OH + OH^- }}$<\/li>\r\n \t<li>$\\ce{\\sf{CH3CH2OH + H2SO4 &lt;=&gt; CH3CH2OH2+ + HSO4- }}$<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<div id=\"s61689\">\r\n<div id=\"section_24\">\r\n\r\n<b>2.\u00a0<\/b>\r\n\r\nIs the following molecule a Br\u00f8nsted acid or base?\r\n\r\nHSO<sub>4<\/sub><sup>\u2212<\/sup>\r\n\r\n<\/div>\r\n<div id=\"section_25\">\r\n<h3>Solutions<\/h3>\r\nAnswer:\r\n<ol>\r\n \t<li>\r\n<ol>\r\n \t<li><img src=\"https:\/\/chem.libretexts.org\/LibreTexts\/Athabasca_University\/Chemistry_350%3A_Organic_Chemistry_I\/Chapter_2%3A_Polar_Covalent_Bonds%3B_Acids_and_Bases\/\/LibreTexts\/Athabasca_University\/Chemistry_350:_Organic_Chemistry_I\/Chapter_2:_Polar_Covalent_Bonds;_Acids_and_Bases\/2.07_Acids_and_Bases:_The_Br\u00f8nsted-Lowry_Definition##fixme\" alt=\"acids and bases identified in ethoxide reaction with water\" \/><\/li>\r\n \t<li><img src=\"https:\/\/chem.libretexts.org\/LibreTexts\/Athabasca_University\/Chemistry_350%3A_Organic_Chemistry_I\/Chapter_2%3A_Polar_Covalent_Bonds%3B_Acids_and_Bases\/\/LibreTexts\/Athabasca_University\/Chemistry_350:_Organic_Chemistry_I\/Chapter_2:_Polar_Covalent_Bonds;_Acids_and_Bases\/2.07_Acids_and_Bases:_The_Br\u00f8nsted-Lowry_Definition##fixme\" alt=\"acids and bases identified in ethanol reaction with sulfuric acid\" \/><\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<strong>S2.7.1<\/strong>\r\n\r\nIt can be both, consider the following schemes:\r\n\r\n<img class=\"internal default\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04154008\/2.7.png\" alt=\"\" width=\"591\" height=\"92\" \/>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_7\">\r\n<h3 class=\"editable\">Contributors<\/h3>\r\n<ul>\r\n \t<li><a class=\"external\" title=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" href=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" target=\"_blank\" rel=\"external nofollow noopener\">Dr. Dietmar Kennepohl<\/a> FCIC (Professor of Chemistry, <a class=\"external\" title=\"http:\/\/www.athabascau.ca\/\" href=\"http:\/\/www.athabascau.ca\/\" target=\"_blank\" rel=\"external nofollow noopener\">Athabasca University<\/a>)<\/li>\r\n \t<li><a title=\"Organic_Chemistry_With_a_Biological_Emphasis\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\" rel=\"internal\">Organic Chemistry With a Biological Emphasis <\/a>by\u00a0<a class=\"external\" title=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" href=\"http:\/\/facultypages.morris.umn.edu\/%7Esoderbt\/\" target=\"_blank\" rel=\"external nofollow noopener\">Tim Soderberg<\/a>\u00a0(University of Minnesota, Morris)<\/li>\r\n \t<li>Prof. Steven Farmer (<a class=\"external\" title=\"http:\/\/www.sonoma.edu\" href=\"http:\/\/www.sonoma.edu\" target=\"_blank\" rel=\"external nofollow noopener\">Sonoma State University<\/a>)<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"elm-header\">\n<div class=\"elm-header-custom\">\n<div class=\"textbox learning-objectives\">\n<h3>Objectives<\/h3>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div id=\"skills\">\n<p>After completing this section, you should be able to<\/p>\n<ol>\n<li>state the Br\u00f8nsted-Lowry definition of an acid and a base.<\/li>\n<li>identify the Br\u00f8nsted-Lowry acid and base in a given acid-base reaction.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Terms<\/h3>\n<div class=\"elm-header\"><\/div>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div>\n<p>Make certain that you can define, and use in context, the key terms below.<\/p>\n<ul>\n<li>acid (Br\u00f8nsted-Lowry)<\/li>\n<li>base (Br\u00f8nsted-Lowry)<\/li>\n<li>conjugate acid<\/li>\n<li>conjugate base<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox\">\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div id=\"note\">\n<h3 class=\"boxtitle\">Study Notes<\/h3>\n<p>You should be familiar with the Br\u00f8nsted-Lowry concept of acidity and the differences between strong and weak acids. You may wish to review this topic before proceeding.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<p>In 1923, chemists Johannes Br\u00f8nsted and Martin Lowry independently developed definitions of acids and bases based on compounds abilities to either donate or accept protons (H<sup>+<\/sup> ions). Here, acids are defined as being able to donate protons in the form of hydrogen ions; whereas bases are defined as being able to accept protons.\u00a0This took the <a title=\"Physical Chemistry\/Acids and Bases\/Acid\/Arrhenius Concept of Acids and Bases\" href=\"\/Physical_Chemistry\/Acids_and_Bases\/Acid\/Arrhenius_Concept_of_Acids_and_Bases\" rel=\"internal\">Arrhenius<\/a> definition one step further as water is no longer required to be present in the solution for acid and base reactions to occur.<\/p>\n<div>\n<div id=\"section_1\">\n<h3 class=\"editable\">Br\u00f8nsted-Lowery Definition<\/h3>\n<p class=\"paragraph\">J.N. Br\u00f8nsted and T.M. Lowry independently developed the theory of proton donors and proton acceptors in acid-base reactions, coincidentally in the same region and during the\u00a0same year. The Arrhenius theory where acids and bases are defined by whether the molecule contains hydrogen and hydroxide ion is too limiting. The main effect of the Br\u00f8nsted-Lowry definition is to identify the proton (H<sup>+<\/sup>) transfer occurring in the acid-base reaction. This is best illustrated in the following equation:<\/p>\n<div>HA+Z\u21ccA\u2212+HZ+<\/div>\n<table style=\"margin: auto;border-spacing: 2px\" cellpadding=\"0\">\n<tbody>\n<tr style=\"height: 16.9062px\">\n<td style=\"height: 16.9062px;width: 33%\">\u00a0<strong>Acid<\/strong><\/td>\n<td style=\"height: 16.9062px;width: 33%\">\u00a0<strong>Base<\/strong><\/td>\n<td style=\"height: 16.9062px;width: 34%\"><\/td>\n<\/tr>\n<tr style=\"height: 28px\">\n<td style=\"height: 28px;width: 33%\">\u00a0<strong>Donates hydrogen ions<\/strong><\/td>\n<td style=\"height: 28px;width: 33%\">\u00a0<strong>Accepts hydrogen ions.<\/strong><\/td>\n<td style=\"height: 28px;width: 34%\"><\/td>\n<\/tr>\n<tr style=\"height: 28px\">\n<td style=\"height: 28px\">\u00a0HCl<sup>+<\/sup><\/td>\n<td style=\"height: 28px\">\u00a0HOH \u2192<\/td>\n<td style=\"height: 28px\">H<sub>3<\/sub>O<sup>+<\/sup> + Cl<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<tr style=\"height: 16px\">\n<td style=\"height: 16px\">\u00a0 HOH<sup>+<\/sup><\/td>\n<td style=\"height: 16px\">\u00a0 NH<sub>3<\/sub>\u2192<\/td>\n<td style=\"height: 16px\">\u00a0NH<sub>4<\/sub><sup>+<\/sup> + OH<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The determination of a substance as a Br\u00f8nsted-Lowery acid or base can only be done by observing the reaction. In the case of the HOH it is a base in the first case and an acid in the second case.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04153952\/180bronsted.gif\" alt=\"180bronsted.gif\" width=\"283px\" height=\"298px\" \/><\/p>\n<p>To determine whether a substance is an acid or a base, count the hydrogens on each substance before and after the reaction. If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions). If the number of hydrogens has increased that substance is the base (accepts hydrogen ions). These definitions are normally applied to the reactants on the left. If the reaction is viewed in reverse a new acid and base can be identified. The substances on the right side of the equation are called conjugate acid and conjugate base compared to those on the left. Also note that the original acid turns in the conjugate base after the reaction is over.<\/p>\n<\/div>\n<div id=\"section_2\">\n<h3 class=\"editable\">Acids are Proton Donors and Bases are Proton Acceptors<\/h3>\n<\/div>\n<\/div>\n<div>\n<p class=\"paragraph\">For a reaction to be in equilibrium a transfer of electrons needs to occur. The acid will give an electron away and the base will receive the electron. Acids and Bases that work together in this fashion are called a <em class=\"italic\">conjugate pair<\/em> made up of <em class=\"italic\">conjugate acids<\/em> and <em class=\"italic\">conjugate bases<\/em>.HA+Z\u21ccA\u2212+HZ+<\/p>\n<p class=\"paragraph\">A stands for an Acidic compound and Z stands for a Basic compound<\/p>\n<ul>\n<li class=\"paragraph\">A Donates H to form HZ<sup class=\"superscript\">+<\/sup>.<\/li>\n<li class=\"paragraph\">Z Accepts H from A which forms HZ<sup class=\"superscript\">+<\/sup><\/li>\n<li class=\"paragraph\">A<sup class=\"superscript\">&#8211;<\/sup> becomes conjugate base of HA and in the reverse reaction it accepts a H from HZ to recreate HA in order to remain in equilibrium<\/li>\n<li class=\"paragraph\">HZ<sup class=\"superscript\">+<\/sup> becomes a conjugate acid of Z and in the reverse reaction it donates a H to A<sup class=\"superscript\">&#8211;<\/sup> recreating Z in order to remain in equilibrium<\/li>\n<\/ul>\n<\/div>\n<div>\n<div id=\"section_3\">\n<div class=\"textbox examples\">\n<h3>Examples<\/h3>\n<div>\n<div id=\"section_3\">\n<h3 class=\"editable\">Questions<\/h3>\n<div class=\"editIcon\"><\/div>\n<ol>\n<li>Why is HA\u00a0an Acid?<\/li>\n<li>Why is A<sup>&#8211;<\/sup>\u00a0a Base?<\/li>\n<li class=\"paragraph\">How can A<sup class=\"superscript\">&#8211;<\/sup> be a base when HA was and Acid?<\/li>\n<li class=\"paragraph\">How can HZ<sup class=\"superscript\">+<\/sup> be an acid when Z used to be a Base?<\/li>\n<li class=\"paragraph\"><strong class=\"bold\">Now that we understand the concept, let&#8217;s look at an an example with actual compounds!<\/strong>\n<div>HCl+H2O\u21ccH3O++Cl\u00af<\/div>\n<\/li>\n<\/ol>\n<ul>\n<li class=\"paragraph\">HCL is the acid because it is donating a proton to H<sub>2<\/sub>O<\/li>\n<li class=\"paragraph\">H<sub>2<\/sub>O is the base because H<sub>2<\/sub>O is accepting a proton from HCL<\/li>\n<li class=\"paragraph\">H<sub>3<\/sub>O<sup class=\"superscript\">+<\/sup> is the conjugate acid because it is donating an acid to CL turn into it&#8217;s conjugate acid H<sub>2<\/sub>O<\/li>\n<li class=\"paragraph\">Cl\u00af is the conjugate base because it accepts an H from H<sub>3<\/sub>O to return to it&#8217;s conjugate acid HCl<\/li>\n<\/ul>\n<p class=\"paragraph\">How can H<sub>2<\/sub>O be a base? I thought it was neutral?<\/p>\n<\/div>\n<\/div>\n<div>\n<div id=\"section_4\">\n<h3 class=\"editable\">Answers<\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q710341\">Show Answer<\/span><\/p>\n<div id=\"q710341\" class=\"hidden-answer\" style=\"display: none\">1. It has a proton that can be transferred<\/p>\n<p>2. It receives a proton from HA<\/p>\n<p>3. A- is a conjugate base because it is in need of a H in order to remain in equilibrium and return to HA<\/p>\n<p>4. HZ+ is a conjugate acid because it needs to donate or give away its proton in order to return to it&#8217;s previous state of Z<\/p>\n<p>5. In the Br\u00f8nsted-Lowry Theory what makes a compound an element or a base is whether or not it donates or accepts protons. If the H2O was in a different problem and was instead donating an H rather than accepting an H it would be an acid!<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div id=\"section_5\">\n<h3 class=\"editable\">\u00a0Conjugate Acid\u2013Base Pairs<\/h3>\n<p>We discussed the concept of conjugate acid\u2013base pairs in Chapter 4, using the reaction of ammonia, the base, with water, the acid, as an example. In aqueous solutions, acids and bases can be defined in terms of the transfer of a proton from an acid to a base. Thus for every acidic species in an aqueous solution, there exists a species derived from the acid by the loss of a proton. These two species that differ by only a proton constitute a <a>conjugate acid\u2013base pair<\/a>. For example, in the reaction of\u00a0<em>HCl\u00a0<\/em>with water (Equation 16.1),\u00a0<em>HCl<\/em>\u00a0, the parent acid, donates a proton to a water molecule, the parent base, thereby forming <em>Cl<sup>&#8211;<\/sup><\/em>. Thus\u00a0<em>Cl<\/em>\u00a0and\u00a0<em>Cl<sup>&#8211;<\/sup><\/em>\u00a0constitute a conjugate acid\u2013base pair. By convention, we always write a conjugate acid\u2013base pair as the acid followed by its conjugate base. In the reverse reaction, the <em>Cl<\/em><sup>&#8211;<\/sup>\u00a0ion in solution acts as a base to accept a proton from\u00a0<em>H<sub>3<\/sub>O<sup>+<\/sup><\/em>, forming\u00a0<em>H<sub>2<\/sub>O<\/em>\u00a0and\u00a0<em>HCl.<\/em>\u00a0Thus <em>H<sub>3<\/sub>O<sup>+<\/sup><\/em>\u00a0and <em>H<sub>2<\/sub>O<\/em>\u00a0constitute a second conjugate acid\u2013base pair. In general, any acid\u2013base reaction must contain two conjugate acid\u2013base pairs, which in this case are\u00a0<em>HCl\/Cl<sup>&#8211;<\/sup><\/em>\u00a0and <em>H<sub>3<\/sub>O<sup>+<\/sup>\/H<sub>2<\/sub>O<\/em>.<\/p>\n<blockquote><p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04153955\/13307049a0af1fc2a8588ee638396963.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/13307049a0af1fc2a8588ee638396963.jpg\" width=\"528\" height=\"170\" \/><\/p>\n<p class=\"boxtitle\">Note<\/p>\n<p>All acid\u2013base reactions contain two conjugate acid\u2013base pairs.<\/p><\/blockquote>\n<p>Similarly, in the reaction of acetic acid with water, acetic acid donates a proton to water, which acts as the base. In the reverse reaction, <em>H<sub>3<\/sub>O<sup>+<\/sup><\/em>\u00a0is the acid that donates a proton to the acetate ion, which acts as the base. Once again, we have two conjugate acid\u2013base pairs: the parent acid and its conjugate base (<i>CH<sub>3<\/sub>CO<sub>2<\/sub>H\/CH<sub>3<\/sub>CO<sub>2<\/sub><sup>&#8211;<\/sup><\/i>) and the parent base and its conjugate acid (<em>H<sub>3<\/sub>O<sup>+<\/sup>\/H<sub>2<\/sub>O<\/em>).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04153958\/0976fc4b1971263ab1f1bf651617f1a6.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/0976fc4b1971263ab1f1bf651617f1a6.jpg\" width=\"502\" height=\"165\" \/><\/p>\n<p>In the reaction of ammonia with water to give ammonium ions and hydroxide ions (Equation 16.3), ammonia acts as a base by accepting a proton from a water molecule, which in this case means that water is acting as an acid. In the reverse reaction, an ammonium ion acts as an acid by donating a proton to a hydroxide ion, and the hydroxide ion acts as a base. The conjugate acid\u2013base pairs for this reaction are <em>NH<sub>4<\/sub><sup>+<\/sup>\/NH<sub>3<\/sub><\/em>\u00a0and <em>H<sub>2<\/sub>O\/OH<sup>&#8211;<\/sup><\/em>. Some common conjugate acid\u2013base pairs are shown in Figure 2.7.1.<\/p>\n<div style=\"width: 560px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"internal\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04154001\/d74ff3bb2b8f11ddd4804cc71e8fcb32.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/d74ff3bb2b8f11ddd4804cc71e8fcb32.jpg\" width=\"550\" height=\"180\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1.\u00a0The Relative Strengths of Some Common Conjugate Acid\u2013Base Pairs<\/p>\n<\/div>\n<\/div>\n<\/div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04154005\/eec51e5746bb3b13108029410ecf1f45.jpg\" alt=\"File:Wikitexts\/UC_Davis\/UCD_Chem_2B\/UCD_Chem_2B:_Larsen\/Unit_III:_Acids_and_Bases\/16.2:_A_Qualitative_Description_of_Acid\u2013Base_Equilibria\/eec51e5746bb3b13108029410ecf1f45.jpg\" width=\"270\" height=\"620\" \/><\/p>\n<p>The strongest acids are at the bottom left, and the strongest bases are at the top right. The conjugate base of a strong acid is a very weak base, and, conversely, the conjugate acid of a strong base is a very weak acid.<\/p>\n<div id=\"section_6\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<h3>Questions<\/h3>\n<ol>\n<li>Identify the Br\u00f8nsted-Lowry acids and bases in the reactions given below.\n<ol>\n<li>$\\ce{\\sf{CH3CH2O^- + H2O &lt;=&gt; CH3CH2OH + OH^- }}$<\/li>\n<li>$\\ce{\\sf{CH3CH2OH + H2SO4 &lt;=&gt; CH3CH2OH2+ + HSO4- }}$<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<div id=\"s61689\">\n<div id=\"section_24\">\n<p><b>2.\u00a0<\/b><\/p>\n<p>Is the following molecule a Br\u00f8nsted acid or base?<\/p>\n<p>HSO<sub>4<\/sub><sup>\u2212<\/sup><\/p>\n<\/div>\n<div id=\"section_25\">\n<h3>Solutions<\/h3>\n<p>Answer:<\/p>\n<ol>\n<li>\n<ol>\n<li><img decoding=\"async\" src=\"https:\/\/chem.libretexts.org\/LibreTexts\/Athabasca_University\/Chemistry_350%3A_Organic_Chemistry_I\/Chapter_2%3A_Polar_Covalent_Bonds%3B_Acids_and_Bases\/\/LibreTexts\/Athabasca_University\/Chemistry_350:_Organic_Chemistry_I\/Chapter_2:_Polar_Covalent_Bonds;_Acids_and_Bases\/2.07_Acids_and_Bases:_The_Br\u00f8nsted-Lowry_Definition##fixme\" alt=\"acids and bases identified in ethoxide reaction with water\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/chem.libretexts.org\/LibreTexts\/Athabasca_University\/Chemistry_350%3A_Organic_Chemistry_I\/Chapter_2%3A_Polar_Covalent_Bonds%3B_Acids_and_Bases\/\/LibreTexts\/Athabasca_University\/Chemistry_350:_Organic_Chemistry_I\/Chapter_2:_Polar_Covalent_Bonds;_Acids_and_Bases\/2.07_Acids_and_Bases:_The_Br\u00f8nsted-Lowry_Definition##fixme\" alt=\"acids and bases identified in ethanol reaction with sulfuric acid\" \/><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<p><strong>S2.7.1<\/strong><\/p>\n<p>It can be both, consider the following schemes:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal default\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/04154008\/2.7.png\" alt=\"\" width=\"591\" height=\"92\" \/><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_7\">\n<h3 class=\"editable\">Contributors<\/h3>\n<ul>\n<li><a class=\"external\" title=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" href=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" target=\"_blank\" rel=\"external nofollow noopener\">Dr. Dietmar Kennepohl<\/a> FCIC (Professor of Chemistry, <a class=\"external\" title=\"http:\/\/www.athabascau.ca\/\" href=\"http:\/\/www.athabascau.ca\/\" target=\"_blank\" rel=\"external nofollow noopener\">Athabasca University<\/a>)<\/li>\n<li><a title=\"Organic_Chemistry_With_a_Biological_Emphasis\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\" rel=\"internal\">Organic Chemistry With a Biological Emphasis <\/a>by\u00a0<a class=\"external\" title=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" href=\"http:\/\/facultypages.morris.umn.edu\/%7Esoderbt\/\" target=\"_blank\" rel=\"external nofollow noopener\">Tim Soderberg<\/a>\u00a0(University of Minnesota, Morris)<\/li>\n<li>Prof. Steven Farmer (<a class=\"external\" title=\"http:\/\/www.sonoma.edu\" href=\"http:\/\/www.sonoma.edu\" target=\"_blank\" rel=\"external nofollow noopener\">Sonoma State University<\/a>)<\/li>\n<\/ul>\n<\/div>\n<\/div>\n","protected":false},"author":311,"menu_order":1,"template":"","meta":{"_candela_citation":"[]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-359","chapter","type-chapter","status-publish","hentry"],"part":20,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/359","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":5,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/359\/revisions"}],"predecessor-version":[{"id":2227,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/359\/revisions\/2227"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/parts\/20"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/359\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/media?parent=359"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=359"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/contributor?post=359"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/license?post=359"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}