{"id":845,"date":"2017-04-24T19:08:04","date_gmt":"2017-04-24T19:08:04","guid":{"rendered":"https:\/\/www.studyorgo.com\/blog\/?p=845"},"modified":"2017-04-24T19:08:04","modified_gmt":"2017-04-24T19:08:04","slug":"in-the-reaction-with-ammonia-why-is-water-the-acid","status":"publish","type":"post","link":"https:\/\/www.studyorgo.com\/blog\/in-the-reaction-with-ammonia-why-is-water-the-acid\/","title":{"rendered":"In the reaction with ammonia, why is water the acid?"},"content":{"rendered":"

In the reaction with ammonia, why is water the acid?<\/em><\/p>\n

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This is a great general chemistry reaction with important organic chemistry implications.\u00a0 Another similar question is, why is water a base when reacted with an \u201cacid\u201d?\u00a0 The answer to both question is: it\u2019s all relative! \u00a0Here at StudyOrgo, we frequently get\u00a0questions like this about topics in organic chemistry that are usually quickly covered, poorly described or expected that you know from previous courses.\u00a0 These concepts are really important to understanding the more complex topics to come. With a membership to StudyOrgo, you will get even more tips and tricks on organic chemistry topics and detailed mechanisms with explanations. \u00a0Today’s blog is a preview of the detailed topics and materials available. \u00a0Check out a\u00a0membership to StudyOrgo.com<\/a>\u00a0and sign up today!<\/p>\n

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Remember that in terms of acids and bases, there are two definitions; the Bronsted and Lewis definition.\u00a0 Bronsted acids are defined as proton donors<\/strong>, while Lewis acids are defined as electron acceptors<\/strong>.\u00a0 Both are acids, but what we think of\u00a0differently is whether protons or electrons are involved.\u00a0 In an aqueous solution, general chemistry or biochemistry, we mainly think of the Bronsted definition because the dissociation of protons from acids changes the solution concentration of H+, which we interpret as a change in pH and the \u201cacidity\u201d of the solution.\u00a0 We measure the dissociation of the protons from acids, or the acceptance of protons by bases, with a numerical value which is the pKa.\u00a0 The greater the pKa, the weaker the acid and stronger the base.\u00a0 The lower the pKa, the stronger the acid and weaker the base. An easy trick for thinking of pKa is, place the protonated version of the molecule on the left and think of it as a proton donor.\u00a0 The pKa tells you how easy this donation will be, the lower the number the easier the proton donation.<\/strong><\/p>\n

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Let\u2019s look at the ammonia and water reaction; the pKa for water is defined as 14.\u00a0 The pKa for ammonia is ~37.<\/p>\n

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Therefore, because the pKa of water is lower than ammonia, it is a stronger acid the ammonia and will donate protons to the ammonia base.\u00a0 This reaction leads water to become the conjugate base OH- and ammonia to become the conjugate acid NH4+.\u00a0 Interestingly, this is why ammonia is a caustic agent, it produces hydroxide that reacts with stains and microorganisms to effectively clean and sanitize household items.\"\"<\/a><\/p>\n

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This is important as an organic chemistry concept because the strength of acids and bases in terms of electrons, or the Lewis definition, is exactly how we think about mechanisms of bond breaking and bond forming; the flow of electrons.\u00a0 The strength of Lewis acids and the conjugated acid can help identify which direction a reaction will proceed.\u00a0 We can see that the reaction of water an ammonia is unfavorable, but enough of the reaction occurs in reality to significantly reduce the pH of water (pH~11 with ammonia).<\/p>\n

Let\u2019s look at an acetylene reacting with a base to generate an alkynide ion, a useful nucleophile for C-C bond formation.\u00a0 If we try to react sodium hydroxide with alkyne, alkynide ion WILL NOT be formed<\/strong>.\u00a0 This is because the conjugate acid product of the reaction is water, which has a pKa of 15, is STRONGER than the original acid acetylene (pKa = 25).\u00a0 Reactions ALWAYS favor formation of the weaker acid, or in this case, the reactant side.<\/p>\n

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If we change our base to sodium amide, which is a much stronger base, alkynide ion WILL be formed<\/strong>.\u00a0 This is because the conjugate acid product of the reaction is ammonia, which has a pKa of 38, and is a WEAKER conjugate acid than the original acid acetylene (pKa = 25).\u00a0 In this case, the reaction favors the product side!<\/p>\n

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In the reaction with ammonia, why is water the acid?   This is a great general chemistry reaction with important organic chemistry implications.\u00a0 Another similar question is, why is water a base when reacted with an \u201cacid\u201d?\u00a0 The answer to both question is: it\u2019s all relative! \u00a0Here at StudyOrgo, we frequently get\u00a0questions like this about […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[1],"tags":[89],"class_list":["post-845","post","type-post","status-publish","format-standard","hentry","category-organic-chemistry","tag-acid-base-organic-chemistry-pka-conguate-acid-equilibrium"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/posts\/845","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/comments?post=845"}],"version-history":[{"count":7,"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/posts\/845\/revisions"}],"predecessor-version":[{"id":859,"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/posts\/845\/revisions\/859"}],"wp:attachment":[{"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/media?parent=845"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/categories?post=845"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.studyorgo.com\/blog\/wp-json\/wp\/v2\/tags?post=845"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}