{"id":906,"date":"2010-09-29T14:00:20","date_gmt":"2010-09-29T12:00:20","guid":{"rendered":"http:\/\/masterorganicchemistry.wordpress.com\/?p=906"},"modified":"2026-01-22T09:41:16","modified_gmt":"2026-01-22T15:41:16","slug":"how-to-use-a-pka-table","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2010\/09\/29\/how-to-use-a-pka-table\/","title":{"rendered":"How to Use a pKa Table"},"content":{"rendered":"<p><strong>A Key Skill &#8211; How To Use A pK<sub>a<\/sub> Table<\/strong><\/p>\n<p>Today we&#8217;ll talk about an incredibly important skill that might take some time to grasp but pays tremendous dividends. We&#8217;ll go through the exact details of how to use pK<sub>a<\/sub> values to tell if an acid base reaction is favorable or unfavorable.<\/p>\n<ul>\n<li>pK<sub>a<\/sub> is the negative logarithm of the acid dissociation constant, K<sub>a<\/sub>, which can be measured experimentally.<\/li>\n<li>pK<sub>a <\/sub>values have been measured for a large number of molecules and are largely related to the most acidic <strong>functional group<\/strong> present in the molecule. A pK<sub>a<\/sub> table is a useful complication of pK<sub>a<\/sub> values.<\/li>\n<li>A <strong>low<\/strong> value of pK<sub>a<\/sub> (e.g. -10) indicates a <strong>strong<\/strong> <strong>acid<\/strong>. A <strong>high<\/strong> value of pK<sub>a<\/sub> (e.g. 50) indicates a <strong>weak<\/strong> <strong>acid<\/strong>.<\/li>\n<li>Acid base reactions have four components: an <strong>acid<\/strong> and a <strong>base<\/strong> exchange a bond to H to give a <strong>conjugate acid<\/strong> and a <strong>conjugate base<\/strong>.<\/li>\n<li>Acid-base reactions can always be written as <strong>equilibria<\/strong>; that is,\u00a0 occurring in a forward or a reverse direction. The favored direction for an acid-base reaction is when a <strong>stronger acid <\/strong>and a<strong> stronger base\u00a0<\/strong>give a\u00a0<strong>weaker acid\u00a0<\/strong>and a\u00a0<strong>weaker base<\/strong>.<\/li>\n<li>One can tell which direction is favored by comparing the pK<sub>a<\/sub> of the acid and the conjugate acid. Formation of the weaker acid (i.e. molecule with the higher pK<sub>a<\/sub>) will be favored.<\/li>\n<li>These concepts can also be applied to other reactions you will learn about later on in the course (e.g. substitution reactions)<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-38708\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/0-summary-how-to-use-a-pka-table-instructions-how-to-identify-weakest-acid-how-to-estimate-equilibrium-constant-of-an-acid-base-reaction.gif\" alt=\"summary-how to use a pka table- instructions - how to identify weakest acid - how to estimate equilibrium constant of an acid base reaction\" width=\"640\" height=\"633\" \/><\/a><\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li><a href=\"#one\">The Acidity Constant K<sub>a<\/sub> and Its Negative Logarithm pK<sub>a<\/sub><\/a><\/li>\n<li><a href=\"#two\">The Four Components of an Acid Base Reaction<\/a><\/li>\n<li><a href=\"#three\">The Principle of Acid-Base Mediocrity<\/a><\/li>\n<li><a href=\"#four\">Using pK<sub>a<\/sub> values and the Principle of Acid-Base Mediocrity To Predict Acid-Base Reactions<\/a><\/li>\n<li><a href=\"#five\">How to Use pK<sub>a<\/sub> Values to Determine Basicity\u00a0<\/a><\/li>\n<li><a href=\"#six\">How to Use a pK<sub>a<\/sub> Table To Determine If An Acid-Base Reaction Is Favorable<\/a><\/li>\n<li><a href=\"#seven\">How To Determine The Acidity of Compounds That Aren&#8217;t On A pK<sub>a<\/sub> Chart<\/a><\/li>\n<li><a href=\"#eight\">Applying pK<sub>a<\/sub> In Substitution Reactions<\/a><\/li>\n<li><a href=\"#nine\">Summary<\/a><\/li>\n<li><a href=\"#notes\">Notes<\/a><\/li>\n<li><a href=\"#quiz\">Quiz Yourself!<\/a><\/li>\n<li><a href=\"#references\">(Advanced) References and Further Reading<\/a><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<hr \/>\n<h2><a id=\"one\"><\/a>1. The Acidity Constant Ka and Its Negative Logarithm pKa<\/h2>\n<p>Let&#8217;s review some key principles of acidity constants to make sure we&#8217;re all on the same page.<\/p>\n<p>The acidity constant, K<sub>a<\/sub>, is a measurement of the equilibrium between an acid, H-A and its dissociation to give H+ and its conjugate base, A(-). <span style=\"color: #993366;\"><em>(This value has to be measured experimentally)<\/em><\/span>.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-30586\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/1-what-is-the-acid-dissociation-constant-ka-and-what-is-the-equilibrium-expression.gif\" alt=\"what is the acid dissociation constant ka and what is the equilibrium expression\" width=\"640\" height=\"419\" \/><\/a><\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li style=\"list-style-type: none;\">\n<ul>\n<li>A <strong>strong acid<\/strong> has complete or nearly complete dissociation, so a <strong>large<\/strong> K<sub>a<\/sub>.<\/li>\n<li>A <strong>weak acid<\/strong> has incomplete dissociation, and a <strong>small<\/strong> K<sub>a<\/sub>.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<p>Not shown in the equation for K<sub>a<\/sub> is the solvent, which is generally assumed to be water for our purposes. <span style=\"color: #993366;\"><em>There are limits to using water as a solvent for K<sub>a<\/sub> measurements at extreme acidities and basicities<\/em><\/span>. [<a href=\"#noteone\"><span style=\"color: #ff0000;\">Note 1<\/span><\/a>]<\/p>\n<p>Can you tell which acid is stronger based on its K<sub>a<\/sub>?<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34790\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34790\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34790\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34790\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34790\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34790 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34790\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-nh21w\" data-id=\"nh21w\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2364-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2364-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>In order to get a better grasp on these numbers, we often take the <strong>negative<\/strong> <strong>logarithm<\/strong> of the acidity constant and call this <strong>pK<sub>a<\/sub><\/strong>.<\/p>\n<p>pK<sub>a<\/sub> = &#8211; log K<sub>a<\/sub><\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34791\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34791\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34791\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34791\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34791\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34791 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34791\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-zr9mp\" data-id=\"zr9mp\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2365-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2365-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li style=\"list-style-type: none;\">\n<ul>\n<li>The <strong>higher<\/strong> the pK<sub>a<\/sub>, the <strong>weaker<\/strong> the acid.<\/li>\n<li>The\u00a0<strong>lower<\/strong> the pK<sub>a<\/sub>, the <strong>stronger<\/strong> the acid.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<p>One of the strongest acids, H-I has a pK<sub>a<\/sub> of -10.<\/p>\n<p>Water has a pK<sub>a<\/sub> of 14. [<a href=\"#notetwo\"><span style=\"color: #ff0000;\">Note 2<\/span><\/a>]<\/p>\n<p>Alkanes have a pK<sub>a<\/sub> of about 50.<\/p>\n<p>[<span style=\"color: #ff0000;\"><a href=\"#notethree\">Note 3<\/a><span style=\"color: #000000;\">]<\/span><\/span><\/p>\n<h2><a id=\"two\"><\/a>2. The Four Components Of An Acid-Base Reaction<\/h2>\n<p>In an acid-base reaction, a bond is<strong> formed<\/strong> at <strong>H <\/strong>and a bond is <strong>broken<\/strong> at <strong>H<\/strong>.<\/p>\n<p>Every acid-base reaction has\u00a0<strong>four<\/strong> components.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-30587\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/5-the-four-components-of-an-acid-base-reaction-are-acid-base-conjugate-acid-and-conjugate-base.gif\" alt=\"the four components of an acid base reaction are acid base conjugate acid and conjugate base\" width=\"640\" height=\"241\" \/><\/a><\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li style=\"list-style-type: none;\">\n<ul>\n<li>The\u00a0<strong>acid<\/strong> (where the bond to H breaks),<\/li>\n<li>the\u00a0<strong>base<\/strong> (where the bond to H forms),<\/li>\n<li>the\u00a0<strong>conjugate acid<\/strong> (the species that results when the base forms the new bond to <strong>H<\/strong>)<\/li>\n<li>and the <strong>conjugate base<\/strong> (the species that results when the acid breaks its bond to\u00a0<strong>H<\/strong>).<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<p>This is drawn in the forward direction (left to right) but the\u00a0<strong>reverse\u00a0<\/strong>reaction (right to left) is also an acid-base reaction. We just flip around the identities.<\/p>\n<p>To see the reverse acid-base reaction, <a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/Supp-1-Reverse-of-acid-base-reaction.gif\" data-link=\"\" data-title=\"\" data-text=\"\">hover here<\/a> or click this <a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/Supp-1-Reverse-of-acid-base-reaction.gif\">link<\/a>.<\/p>\n<p>Note that by drawing something up as an acid-base reaction does <strong>not<\/strong> imply that it <strong>actually happens<\/strong> at a reasonable rate.<\/p>\n<p>That can only be determined through experiment.<\/p>\n<p>We&#8217;re just saying that the\u00a0<strong>pattern<\/strong> of an acid-base reaction is followed (i.e. form and break a bond at the same H).<\/p>\n<h2><a id=\"three\"><\/a>3. The Principle of Acid-Base Mediocrity<\/h2>\n<p>In what direction do you think acid-base reactions are favored?<\/p>\n<p>Do they spontaneously go from stronger acids to weaker acids, or do they go from weaker acids to stronger acids?<\/p>\n<p>What correlates more with your experience: does adding salt (NaCl) to water result in harmless salt water, or result in the exothermic formation of HCl gas and caustic NaOH?<\/p>\n<p><strong>Acid base reactions spontaneously proceed in a direction that gives weaker acids from stronger acids<\/strong><\/p>\n<p>I like to call this The Principle of Acid-Base Mediocrity. [<span style=\"color: #ff0000;\"><a href=\"#notefour\">Note 4<\/a><span style=\"color: #000000;\">]<\/span><\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-30588\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/6-the-favored-direction-for-an-acid-base-reaction-is-one-where-a-stronger-acid-combines-with-a-stronger-base-and-a-weaker-acid-and-a-weaker-base.gif\" alt=\"the favored direction for an acid base reaction is one where a stronger acid combines with a stronger base and a weaker acid and a weaker base\" width=\"640\" height=\"427\" \/><\/a><\/p>\n<p>How do we know which acid is stronger and which is weaker? By identifying the <strong>acid<\/strong> and the <strong>conjugate acid<\/strong>, and <strong>comparing their two pK<sub>a<\/sub> values<\/strong>!<\/p>\n<p>Acid base reactions will favor formation of the acid with the higher pK<sub>a<\/sub> value. It&#8217;s not completely unlike how areas of high pressure will flow to areas of low pressure.<\/p>\n<h2><a id=\"four\"><\/a>4. Using pKa values and the Principle of Acid-Base Mediocrity To Predict Acid-Base Reactions<\/h2>\n<p>With these two mental tools &#8211; the higher the pK<sub>a<\/sub>, the weaker the acid, and the Principle Of Acid Base Mediocrity, we are all set to use <strong>pK<sub>a<\/sub> values<\/strong> to <strong>predict<\/strong> the directions of acid-base reactions.<\/p>\n<p>The acid-base reaction that results in a compound with a lower pK<sub>a<\/sub> going to a higher pK<sub>a<\/sub> will be favored.<\/p>\n<p>The compound with the <strong>lower<\/strong> <strong>pK<sub>a<\/sub> <\/strong>will be the <strong>stronger<\/strong> acid and the compound with the <strong>higher<\/strong> <strong>pK<sub>a<\/sub><\/strong> will be the <strong>weaker<\/strong> acid.<\/p>\n<p>Ready for some quizzes?<\/p>\n<p>Let&#8217;s start with an acid base reaction involving a terminal alkyne (pK<sub>a<\/sub> 25) and acetic acid (pK<sub>a<\/sub> 4)<\/p>\n<p>[<div class=\"wq-quiz-wrapper\" data-id=\"34792\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34792\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34792\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34792\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34792\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34792 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34792\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-lakvh\" data-id=\"lakvh\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2367-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2367-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper --><\/p>\n<p>Now let&#8217;s look at water (pK<sub>a<\/sub> 14) and acetic acid (pK<sub>a<\/sub> 4)<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34793\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34793\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34793\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34793\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34793\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34793 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34793\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-6uycx\" data-id=\"6uycx\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2368-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2368-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>Note that each unit of difference in pK<sub>a<\/sub> indicates an order of magnitude difference in acidity.<\/p>\n<p>We can get a rough idea of the position of the equilibrium by measuring the difference in pK<sub>a<\/sub> values.<\/p>\n<p>So the acid-base reaction in the quiz above favors water (pK<sub>a<\/sub> 14) by about 10 orders of magnitude (10<sup>10<\/sup>) over acetic acid (pK<sub>a<\/sub> 4). That means there are roughly 10 billion molecules of water for every molecule of acetic acid.<\/p>\n<p>This quiz asks you to calculate the ratio of each acid present at equilibrium.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34794\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34794\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34794\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34794\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34794\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34794 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34794\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-1qpc6\" data-id=\"1qpc6\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2369-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2369-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>A good rule of thumb is that a difference in pK<sub>a<\/sub> of more than 10 pK<sub>a<\/sub> units will represent an <strong>irreversible<\/strong> acid-base reaction for the purposes of carrying out a chemical reaction. [<a href=\"#notefive\"><span style=\"color: #ff0000;\">Note 5<\/span><\/a>]<\/p>\n<p>So acetate ion (the conjugate base of acetic acid, pK<sub>a<\/sub> 4) is perfectly capable of deprotonating water (pK<sub>a<\/sub> 14) but the equilibrium will be very unfavorable (a difference of 10 pK<sub>a<\/sub> units).<\/p>\n<p>It&#8217;s unreasonable to expect that acetate ion will be able to deprotonate a ketone like acetone (pK<sub>a<\/sub> 17) to any significant extent.<\/p>\n<h2><a id=\"five\"><\/a>5. pKa Values Are Also A Guide To Basicity<\/h2>\n<p>pK<sub>a<\/sub> values are also a useful guide to basicity, but maybe not in the way that you&#8217;d normally think.<\/p>\n<p>There&#8217;s one common misconception that needs to get cleared up.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34795\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34795\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34795\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34795\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34795\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34795 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34795\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-38whb\" data-id=\"38whb\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2370-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2370-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>It&#8217;s true that the <strong>higher<\/strong> the <strong>pK<sub>a<\/sub><\/strong>, the <strong>weaker<\/strong> the <strong>acid<\/strong>.<\/p>\n<p>Does that mean that the <strong>higher<\/strong> the <strong>pK<sub>a<\/sub><\/strong>, the <strong>stronger<\/strong> the <strong>base<\/strong>?<\/p>\n<p><strong>No!\u00a0<\/strong><\/p>\n<p>In order for a species to act as a base, it has to have a lone pair of electrons that could reasonably remove a proton. That&#8217;s not the case for alkanes (pK<sub>a<\/sub> = 50), alkenes (pK<sub>a<\/sub> = 42), or ammonium salts (pK<sub>a<\/sub> = 10) and many others.<\/p>\n<p>Instead, it&#8217;s true that the<strong> higher the pK<sub>a<\/sub>, the stronger the<\/strong>\u00a0<strong>conjugate base<\/strong>.<\/p>\n<p>You <strong>can<\/strong> use pK<sub>a<\/sub> values to predict the strength of the base that will result when a proton (H+) is removed.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34796\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34796\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34796\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34796\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34796\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34796 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34796\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-2ovw8\" data-id=\"2ovw8\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2371-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2371-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>Here is another quick quiz:<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34797\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34797\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34797\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34797\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34797\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34797 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34797\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-xudtj\" data-id=\"xudtj\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2372-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2372-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<h2><a id=\"six\"><\/a>6. How To Use a pKa table<\/h2>\n<p>The ultimate guide to acidity is a pK<sub>a<\/sub> table, which represents a collection of <strong>actual measurements<\/strong> of the acidity of various molecules.<\/p>\n<p>A typical pK<sub>a<\/sub> table covers the acidity of species ranging from hydroiodic acid H-I (pK<sub>a<\/sub> = -9) to alkanes (pK<sub>a<\/sub> = 50)\u00a0 representing about <strong>60 orders of magnitude<\/strong> in reactivity. [<a href=\"#notesix\"><span style=\"color: #ff0000;\">Note 6<\/span><\/a>]<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-30589\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/13-a-short-pka-table-with-ranked-acids-and-also-a-ranking-of-the-basicity-of-the-conjugate-bases.gif\" alt=\"a short pka table with ranked acids and also a ranking of the basicity of the conjugate bases\" width=\"640\" height=\"644\" \/><\/a><\/p>\n<p>Using a pK<sub>a<\/sub> table, you can apply the Principle of Acid-Base Mediocrity and examine any random acid base reaction, once you have identified the main functional group.<\/p>\n<p>It&#8217;s very powerful.<\/p>\n<p>For example, will CH<sub>3<\/sub>CH<sub>2<\/sub>S(-), the conjugate base of ethanethiol \u00a0deprotonate hydrogen gas (H<sub>2<\/sub>) to give H(-) ?<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34798\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34798\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34798\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34798\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34798\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34798 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34798\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-q5m0u\" data-id=\"q5m0u\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2373-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2373-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>To figure this out, we draw out the four components of our acid base reaction. We then look on our pK<sub>a<\/sub> table for the pK<sub>a<\/sub> of a <strong>thiol<\/strong> and H<sub>2<\/sub> . The pK<sub>a<\/sub> of the thiol is about 10 and the pK<sub>a<\/sub> of H<sub>2<\/sub> is about 35.<\/p>\n<p>Since going from CH<sub>3<\/sub>CH<sub>2<\/sub>S(-) to H(-) would result in a significantly stronger acid (and stronger base), we can say this reaction is\u00a0<strong>unfavorable<\/strong>.<\/p>\n<p>With a little bit of thought, you will soon reach the conclusion that a pK<sub>a<\/sub> table is not unlike the ranking of hands in poker.<\/p>\n<p>It is particularly useful for ranking the strengths of bases.<\/p>\n<p>For example, just like a royal flush beats all other hands in poker, a deprotonated alkane like CH<sub>3<\/sub>(-) will have a favorable acid-base equilibrium for the deprotonation of\u00a0 <strong>anything below it in the pK<sub>a<\/sub> table. <\/strong><\/p>\n<p>Since pretty much everything is less acidic than an alkane, this means that the conjugate base of an alkane can remove a proton from a huge variety of functional groups. [<a href=\"#noteseven\"><span style=\"color: #ff0000;\">Note 7<\/span><\/a>]<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-30590\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/15-how-to-use-a-pka-table-to-rank-the-basicity-of-conjugate-bases.gif\" alt=\"how to use a pka table to rank the basicity of conjugate bases\" width=\"640\" height=\"533\" \/><\/a><\/p>\n<h2><a id=\"seven\"><\/a>7. How To Determine The Acidity Of Compounds That Aren&#8217;t on the pK<sub>a<\/sub> chart<\/h2>\n<p>One of the keys to using a pK<sub>a<\/sub> table is to start by <strong>identifying the key functional group<\/strong>(s) present and\u00a0<strong>be familiar with their acidities.<\/strong><\/p>\n<p>Two of the molecules below might look a little scary because they are so huge and complex, but their <strong>acidity <\/strong>will mostly be\u00a0determined by the <strong>functional group<\/strong>, not all the alkyl carbons.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-30591\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/16-how-to-use-a-pka-table-to-determine-acidity-of-complex-molecules.gif\" alt=\"how to use a pka table to determine acidity of complex molecules\" width=\"640\" height=\"363\" \/><\/a><\/p>\n<p>The pK<sub>a<\/sub> of cholic acid isn&#8217;t so different from acetic acid. The pK<sub>a<\/sub> of cocaine&#8217;s conjugate acid isn&#8217;t so different from ammonium. So start by focusing on the <strong>most acidic<\/strong> functional group.<\/p>\n<p>What about the key trends that influence acidity? Aren&#8217;t they important?<\/p>\n<p>Yes, of course. But\u00a0when we&#8217;re <strong>changing<\/strong> two or more variables at once <span style=\"color: #993366;\"><em>(e.g. when we&#8217;re comparing the acidities of two different functional groups)<\/em><\/span>, it&#8217;s difficult to judge which variable is more important without an experimental measurement.<\/p>\n<p>That&#8217;s why pK<sub>a<\/sub> measurements are so useful.<\/p>\n<p>If we&#8217;re examining the\u00a0<strong>same<\/strong> functional group, then applying <strong>trends<\/strong> to determine the relative acidities is helpful.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-30592\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/10\/17-instead-of-using-a-pka-table-when-there-are-molecules-with-the-same-functional-group-apply-trends-instead.gif\" alt=\"instead of using a pka table when there are molecules with the same functional group apply trends instead\" width=\"639\" height=\"224\" \/><\/a><\/p>\n<p>In this case, apply the trend that the more electronegative electron-withdrawing groups help to stabilize the negative charge in the conjugate base. The weaker the conjugate base, the stronger the acid.<\/p>\n<h2><a id=\"eight\"><\/a>8. Not Just For Acid Base Reactions<\/h2>\n<p>A good working knowledge of pK<sub>a<\/sub> isn&#8217;t just useful for acid-base reactions.<\/p>\n<p>It can also be useful for predicting whether certain reactions will be favorable, <strong>even if you don&#8217;t know the mechanism<\/strong>.<\/p>\n<p>For example,\u00a0 <strong>substitution reactions<\/strong> involve formation and breakage of bonds at a carbon atom.<\/p>\n<p>Here is an example.<\/p>\n<p>Just based on relative basicities, in which direction would you predict this reaction to be favorable?<strong> Don&#8217;t worry about anything else for now.\u00a0<\/strong><\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34799\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34799\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34799\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34799\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34799\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34799 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34799\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-2fqw8\" data-id=\"2fqw8\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2374-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2374-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>We would not expect this reaction to be favorable, because it results in a much stronger base.<\/p>\n<p>But the reverse reaction, where it does form a weaker base, works perfectly fine.<\/p>\n<p>Here is another examnple of a substitution reaction, known as nucleophilic acyl substitution. Don&#8217;t worry about the name or the mechanism for now.<\/p>\n<p>Just based on relative pK<sub>a<\/sub> values, in which direction would you predict this reaction to be favorable?<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"34800\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"34800\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"34800\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"34800\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-34800\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-34800 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"34800\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-sps64\" data-id=\"sps64\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2375-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2375-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>All else being equal, we should expect that the reaction will favor the formation of the\u00a0<strong>weaker base<\/strong>.<\/p>\n<h2><a id=\"nine\"><\/a>9. Summary<\/h2>\n<p>If you have a pK<sub>a<\/sub> table, you essentially have a ranking of the stabilities of different molecules. (The stronger the base, the more unstable it is).<\/p>\n<p>You can start to make predictions about which direction reactions will be favorable (or unfavorable).<\/p>\n<p>When you hear instructors say things like, &#8220;don&#8217;t memorize, learn the concepts! &#8220;, <strong>this is one of those concepts that is extremely powerful when you understand it and apply it<\/strong>.<\/p>\n<hr \/>\n<h2><a id=\"notes\"><\/a>Notes<\/h2>\n<div class=\"related-articles\"><p><strong>Related Articles<\/strong><\/p><ul><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2010\/06\/18\/know-your-pkas\/\" class=\"\"><span>The pKa Table Is Your Friend<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/01\/25\/putting-acidity-in-perspective\/\" class=\"\"><span>pKa Values Span 60 Orders Of Magnitude<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/05\/09\/acid-base-reactions-ka-and-pka\/\" class=\"\"><span>Acid-Base Reactions: Introducing Ka and pKa<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/04\/18\/basicity-of-amines-and-pkah\/\" class=\"\"><span>Basicity of Amines And pKaH<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/05\/06\/nucleophilic-acyl-substitution\/\" class=\"\"><span>Nucleophilic Acyl Substitution (With Negatively Charged Nucleophiles)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/04\/12\/what-makes-a-good-leaving-group\/\" class=\"\"><span>What makes a good leaving group?<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2010\/09\/22\/five-key-factors-that-influence-acidity\/\" class=\"\"><span>Five Key Factors That Influence Acidity<\/span><\/a><\/li><\/ul><\/div>\n<p><strong><a id=\"noteone\"><\/a>Note 1<\/strong>. The limit to using water as solvent for pK<sub>a<\/sub> measurements is the levelling effect. That is, no base can exist that is stronger than HO(-), and no acid can exist that is stronger than H<sub>3<\/sub>O(+). For this reason, pK<sub>a<\/sub> values for weaker acids than H<sub>2<\/sub>O are often measured in DMSO.<\/p>\n<p><strong><a id=\"notetwo\"><\/a>Note 2<\/strong>. The pK<sub>a<\/sub> of pure water is 14. The relative acidity of water relative to alcohols can change in other solvents. For example, in 2-propanol, methanol is 3 times more acidic than water.\u00a0 See Ref 1.<\/p>\n<p><strong><a id=\"notethree\"><\/a>Note 3<\/strong>. How are pK<sub>a<\/sub> values measured? See<a href=\"#refsix\"> reference six<\/a>.<\/p>\n<p><strong><a id=\"notefour\"><\/a>Note 4<\/strong>. Related to the Principle of Acid-Base Mediocrity is the Principle of <strong>Pressure Mediocrity<\/strong> (high pressure flows to low pressure, to give a mediocre pressure) and the Principle of <strong>Concentration Mediocrity<\/strong> (high concentration diffuses to areas of low concentration to give a mediocre concentration).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-31453\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/Law-of-pressure-mediocrity-flowing-from-high-pressure-to-low-TN-vs-Bama.jpg\" alt=\"Law of pressure mediocrity - flowing from high pressure to low - TN vs Bama\" width=\"400\" height=\"500\" srcset=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/Law-of-pressure-mediocrity-flowing-from-high-pressure-to-low-TN-vs-Bama.jpg 1080w, https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/Law-of-pressure-mediocrity-flowing-from-high-pressure-to-low-TN-vs-Bama-240x300.jpg 240w, https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/Law-of-pressure-mediocrity-flowing-from-high-pressure-to-low-TN-vs-Bama-819x1024.jpg 819w, https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/Law-of-pressure-mediocrity-flowing-from-high-pressure-to-low-TN-vs-Bama-768x960.jpg 768w, https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2010\/09\/Law-of-pressure-mediocrity-flowing-from-high-pressure-to-low-TN-vs-Bama-608x760.jpg 608w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><\/a><\/p>\n<p><strong><a id=\"notefive\"><\/a>Note 5<\/strong>. One example of this rule of thumb in practice is the <a href=\"https:\/\/www.masterorganicchemistry.com\/2020\/09\/14\/claisen-condensation-and-dieckmann-condensation\/\">Claisen Condensation<\/a>, where alkoxide bases (pK<sub>a<\/sub> of alcohols = 15-16) are capable of deprotonating esters (pK<sub>a<\/sub> = 25).<\/p>\n<p><strong><a id=\"notesix\"><\/a>Note 6<\/strong>. 60 orders of magnitude is a <strong>lot<\/strong>. It is roughly the difference between the smallest possible length (the Planck length, about 10<sup>-35<\/sup> m) and the size of the known universe (4.4 \u00d7 10<sup>26<\/sup> m).<\/p>\n<p><strong><a id=\"noteseven\"><\/a>Note 7<\/strong>. Assuming no side reactions interfere, which is generally a good assumption since, for the most part, acid-base reactions are fast, relative to other reactions.<\/p>\n<h2><a id=\"quiz\"><\/a>Quiz Yourself<\/h2>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2366-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2376-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3326-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3315-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3327-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n<hr \/>\n<h2><a id=\"references\"><\/a>(Advanced) References and Further Reading<\/h2>\n<p>A collection of pKa values is presented on the <a href=\"https:\/\/organicchemistrydata.org\/hansreich\/resources\/pka\/\">Organic Chemistry Data<\/a> site (formerly Hans Reich&#8217;s site)<\/p>\n<ol>\n<li><strong><a href=\"https:\/\/chem.libretexts.org\/Bookshelves\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Fundamentals\/What_is_the_pKa_of_water\">What Is The pKa of Water<\/a><\/strong>? from Libretexts is a very accessible article on this topic.<\/li>\n<li><strong>pKa Values in the Undergraduate Curriculum: What Is the Real pKa of Water?<\/strong><br \/>\nTodd P. Silverstein and Stephen T. Heller<br \/>\n<em>Journal of Chemical Education<\/em> <strong>2017<\/strong> 94 (6), 690-695<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/acs.jchemed.6b00623\">10.1021\/acs.jchemed.6b00623<\/a><\/li>\n<li><strong>Confusing Quantitative Descriptions of Br\u00f8nsted-Lowry Acid-Base Equilibria in Chemistry Textbooks \u2013 A Critical Review and Clarifications for Chemical Educators<\/strong><br \/>\nMeister, E.C., Willeke, M., Angst, W., Togni, A. and Walde, P.<br \/>\nHelvetica Chimica Acta,\u00a0<strong>2014<\/strong>\u00a097: 1-31.<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/doi.org\/10.1002\/hlca.201300321\">10.1002\/hlca.201300321<\/a><br \/>\nFull discussion of why the pK<sub>a<\/sub> of water (in water as solvent) should be 14.0 and the pKa of H3O(+) should be 0.<\/li>\n<li><strong>Acid Ionization Constants of Alcohols. II. Acidities of Some Substituted Methanols and Related Compounds<\/strong><br \/>\nP. Ballinger and F. A. Long<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1960<\/strong> 82 (4), 795-798<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/ja01489a008\">10.1021\/ja01489a008<\/a><br \/>\nThis is the paper giving the pK<sub>a<\/sub> of water as 15.7 whose methods are criticized in the above articles. Read it for yourself.<\/li>\n<li><strong>The Relative Acidity of Water, Methanol and Other Weak Acids in Isopropyl Alcohol Solution<\/strong><br \/>\nJack Hine and Mildred Hine<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1952<\/strong> 74 (21), 5266-5271<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01141a009\">10.1021\/ja01141a009<\/a><\/li>\n<li><strong><a id=\"refsix\"><\/a>Equilibrium acidities in dimethyl sulfoxide solution<\/strong><br \/>\nFrederick G. Bordwell<br \/>\n<em>Accounts of Chemical Research<\/em> <strong>1988<\/strong> 21 (12), 456-463<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ar00156a004\">10.1021\/ar00156a004<\/a><br \/>\nA very accessible account on the measurement of pKa values.<\/li>\n<\/ol>\n<p>[Sigificantly updated Oct 2022]<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Today we&#8217;ll talk about an incredibly important skill that might take some time to grasp but pays tremendous dividends. We&#8217;ll go through the exact details of how to use a pKa table. Understanding the proper use of a pKa table will give you the ability to recognize which acid-base reactions will happen and which will not. This will come up a lot as you progress through Org 1 and Org 2. It might be helpful to go back and review some of the factors that affect acidity that were talked about earlier.<\/p>\n","protected":false},"author":1,"featured_media":38708,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1407],"tags":[163,164,176,177,688,586,513,255,270,514],"post_folder":[],"class_list":["post-906","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-acid-base-reactions","tag-acidity","tag-acids","tag-bases","tag-basicity","tag-conjugate-acid","tag-conjugate-base","tag-equilibrium","tag-pka-tables","tag-skills","tag-stability"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>How To Use a pKa Table<\/title>\n<meta name=\"description\" content=\"Understanding the proper use of a pKa table will give you the ability to recognize which acid-base reactions will happen and which will not. 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