{"id":522,"date":"2017-08-21T10:01:42","date_gmt":"2017-08-21T10:01:42","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/chemistry\/?page_id=522"},"modified":"2017-09-20T19:16:26","modified_gmt":"2017-09-20T19:16:26","slug":"the-development-and-theories-of-acids-and-bases","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/chemistry\/the-development-and-theories-of-acids-and-bases\/","title":{"rendered":"The Development and Theories of Acids and Bases"},"content":{"rendered":"<div class=\"twelve columns\" style=\"margin-top: 10%;\">\n<div class=\"advance\">\n<p><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/colligative-properties-and-related-laws\">\u2b05 Previous Lesson<\/a>\u00a0<a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/gas-laws-and-solutions\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/relationships-between-acids-bases-and-salts\">Next Lesson \u27a1<\/a><\/p>\n<\/div>\n<p><!-- UPDATE NEXT\/PREVIOUS ABOVE --><\/p>\n<p><!-- CONTENT STARTS HERE --><\/p>\n<h1 id=\"title\">The Development and Theories of Acids and Bases<\/h1>\n<h4>Objective<\/h4>\n<p>In this lesson we will examine three of the main theories used to define acids and bases, review the pH\u00a0scale, its applications, and its development, as well as identify acids and bases as strong or weak,\u00a0based on their dissociation.<\/p>\n<h4>Previously we covered&#8230;<\/h4>\n<ul>\n<li>To complete calculations in this section we should be comfortable working with molality.<\/li>\n<li>Calculating the theoretical freezing point and boiling point of a solution<\/li>\n<li>Calculating the molar mass of a solute based on freezing point depression or boiling point elevation data<\/li>\n<li>Using Henry\u2019s Law to predict the concentration of gases in a mixture<\/li>\n<li>Using Raoult\u2019s Law to calculate the vapor pressure over a solution containing a nonvolatile solute over a solution containing two volatile liquids<\/li>\n<\/ul>\n<section>\n<h3>What are Acids and Bases?<\/h3>\n<p>The terms acid and base are often used to classify substances used in chemical reactions. The\u00a0specific definition of each term depends on which acid-base theory we choose to use. The three main\u00a0acid-base definitions we should be familiar with are those credited to Arrhenius, Br\u00f8nsted-Lowry,\u00a0and Lewis.<\/p>\n<h3>Arrhenius Concept<\/h3>\n<p>The Arrhenius Concept defines acids as substances that produce H<sup>+<\/sup> (hydrogen ions) in\u00a0solution.<\/p>\n<p class=\"center\">HCl(<em>aq<\/em>) \u2192 H<sup>1+<\/sup>(<em>aq<\/em>)\u00a0+ Cl<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p class=\"center\">H<sub>3<\/sub>PO<sub>4<\/sub>(<em>aq<\/em>) \u2192 3H<sup>1+<\/sup>(<em>aq<\/em>) + PO<sub>4<\/sub><sup>3\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p>According to this concept, hydrochloric and phosphoric acids are acids because they dissociate to\u00a0make hydrogen ions in solution.<\/p>\n<p>It defines bases as substances that produce OH<sup>\u2013<\/sup> (hydroxide ions) in solution.<\/p>\n<p class=\"center\">NaOH(<em>aq<\/em>) \u2192 Na<sup>1+<\/sup>(<em>aq<\/em>) +\u00a0OH<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p class=\"center\">Ca(OH)<sub>2<\/sub>(<em>aq<\/em>) \u2192 Ca<sup>2+<\/sup>(<em>aq<\/em>) + 2OH<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p>According to this concept, sodium and calcium hydroxides are bases because they dissociate to make\u00a0hydroxide ions in solution.<\/p>\n<h3>Br\u00f8nsted-Lowry Model<\/h3>\n<p>The Br\u00f8nsted-Lowry Model defines acids as proton donors. In other words, acids <em>donate<\/em> H<sup>+\u00a0<\/sup>(hydrogen ions) in solution.<\/p>\n<p class=\"center\">HCl(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192 H<sub>3<\/sub>O<sup>1+<\/sup>(<em>aq)<\/em> + Cl<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p class=\"center\">H<sub>3<\/sub>PO<sub>4<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192 H<sub>3<\/sub>O<sup>1+<\/sup>(<em>aq<\/em>)\u00a0+ H<sub>2<\/sub>PO<sub>4<\/sub><sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p>According to this model, hydrochloric and phosphoric acids are acids because they donate a hydrogen\u00a0ion to the water forming the hydronium ion.<\/p>\n<p>It defines bases as proton acceptors. In other words, bases <em>accept<\/em> H<sup>+<\/sup> (hydrogen\u00a0ions) in solution.<\/p>\n<p class=\"center\">NH<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>)\u00a0\u2192 NH<sub>4<\/sub><sup>1+<\/sup>(<em>aq<\/em>)\u00a0+ OH<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p>According to this model, NH<sub>3<\/sub>(<em>aq<\/em>) is a base because it accepts a hydrogen ion to\u00a0form an ammonium ion.<\/p>\n<p>The first equation sets up two interesting relationships. Not only does the ammonia accept a\u00a0hydrogen ion to become the ammonium ion, the hydroxide ion could accept a hydrogen ion from the\u00a0ammonium and become water. These two relationships make the ammonia\/ammonium ion and the\u00a0water\/hydroxide ion <abbr title=\"Pairs of acids and bases that differ only by a single hydrogen ion\">conjugate\u00a0acid\/base pairs<\/abbr>.<\/p>\n<h3>Lewis\u2019 Theory<\/h3>\n<p>In Lewis\u2019 Theory, acids are electron pair <em>acceptors<\/em> in solution, while bases are electron\u00a0pair <em>donors<\/em> in solution.<\/p>\n<p class=\"center\" style=\"text-align: center;\">BF<sub>3<\/sub>(<em>aq<\/em>) + :NH<sub>3<\/sub>(<em>aq<\/em>) \u2192 F<sub>3<\/sub>B:NH<sub>3<\/sub><\/p>\n<p>According to this theory, BF<sub>3<\/sub>(<em>aq<\/em>) is an acid because it accepts the\u00a0electron pair from NH<sub>3<\/sub>(<em>aq<\/em>) which is the base because it donates the electron\u00a0pair to BF<sub>3<\/sub>(<em>aq<\/em>).<\/p>\n<h3>The pH Scale<\/h3>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"u-pull-right padding\" src=\"http:\/\/americanboard.org\/Subjects\/Images\/chemistry\/img\/gaslaw\/DevelopmentAcidsandBases4.phtable.jpg\" width=\"217\" height=\"414\" \/><\/p>\n<p>pH represents the relative acidity of a solution based on hydrogen ion or hydronium ion\u00a0concentration and can be found using either of the following equations:<\/p>\n<p><center><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/Images\/chemistry\/img\/gaslaw\/s5_001.gif\" width=\"268\" height=\"25\" \/><\/center>Since concentrations can be large or small such as 12 M or 4.2\u00d710<sup>\u201313\u00a0<\/sup>M, sometimes it is hard to compare the [H<sub>3<\/sub>O<sup>1+<\/sup>]. The pH scale was developed to\u00a0make it easier to recognize if a substance was acidic or basic.<\/p>\n<p>The <abbr title=\"A substance that is able to act as either an acid or a base\">amphoteric<\/abbr> nature of pure\u00a0water contributes to its neutral nature. This means that water can act as an acid or a base due to\u00a0the concept known as autoionization, which is shown in the following two examples.<\/p>\n<p class=\"center\">H<sub>2<\/sub>O(<em>l<\/em>) \u2192 H<sup>1+<\/sup>(<em>aq<\/em>)\u00a0+ OH<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p>According to the Arrhenius Concept, water (in the equation above) is acting as an acid by producing\u00a0hydrogen ions as well as a base by producing hydroxide ions.<\/p>\n<p class=\"center\">2H<sub>2<\/sub>O(<em>l<\/em>) \u2192 H<sub>3<\/sub>O<sup>1<\/sup><sup>+<\/sup>(<em>aq<\/em>)\u00a0+ OH<sup>1\u2013<\/sup>(<em>aq<\/em>)<\/p>\n<p>According to the Br\u00f8nsted-Lowry Model one water molecule (in the equation above) is acting as an\u00a0acid by donating a hydrogen ion to the other molecule of water forming a hydronium ion. The water\u00a0molecule that is accepting the hydrogen ion is acting as the base.<\/p>\n<p>If we write the equilibrium expression for this we get:<\/p>\n<p class=\"center\">K<sub>w<\/sub> = [H<sub>3<\/sub>O<sup>1+ <\/sup>][OH<sup>1\u2013<\/sup> ] = 1.0\u00d710<sup>\u201314\u00a0<\/sup>at 25 \u00b0C<\/p>\n<p>We can solve for the [H<sub>3<\/sub>O<sup>1+<\/sup> ] or [OH<sup>1\u2013<\/sup> ] based on the\u00a0previous equation.<\/p>\n<p class=\"center\" style=\"text-align: center;\">For every H<sub>3<\/sub>O<sup>1+<\/sup> produced, one OH<sup>1\u2013<\/sup> is made so:<br \/>\n[H<sub>3<\/sub>O<sup>1+<\/sup> ][OH<sup>1\u2013 <\/sup>] = 1.0\u00d710<sup>\u201314<\/sup> becomes<br \/>\n[<em>x<\/em>][<em>x<\/em>] = 1.0\u00d710<sup>\u201314<br \/>\n<\/sup><em>x<\/em><sup>2<\/sup> = 1.0\u00d710<sup>\u201314<br \/>\n<\/sup><em>x<\/em> = 1.0\u00d710<sup>\u20137<br \/>\n<\/sup>Therefore, [H<sub>3<\/sub>O<sup>1+ <\/sup>] = 1.0\u00d710<sup>\u20137<\/sup> = [OH<sup>1\u2013<\/sup>]<br \/>\nIf you are given either the [H<sub>3<\/sub>O<sup>1+<\/sup> ] or [OH<sup>1\u2013 <\/sup>], you can\u00a0solve for the other.<\/p>\n<h4>Sample Problem<\/h4>\n<p>Given [OH<sup>1\u2013 <\/sup>] = 1.0\u00d710<sup>-5<\/sup> M at 25\u00b0C, solve for [H<sub>3<\/sub>O<sup>1+ <\/sup>].<\/p>\n<p class=\"center\" style=\"text-align: center;\">K<sub>w<\/sub> = [H<sub>3<\/sub>O<sup>1+<\/sup> ][OH<sup>1\u2013<\/sup> ] =\u00a01.0\u00d710<sup>\u201314<\/sup> M<sup>2<\/sup><br \/>\n[H<sub>3<\/sub>O<sup>1+<\/sup> ][1.0\u00d710<sup>-5<\/sup> M] = 1.0\u00d710<sup>\u201314<\/sup> M<sup>2<br \/>\n<\/sup><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/Images\/chemistry\/img\/gaslaw\/s5_016.gif\" width=\"282\" height=\"46\" \/><\/p>\n<p>Substances other than water can also be amphoteric. Let\u2019s look at a hydrated aluminum hydroxide ion\u00a0as an example.<\/p>\n<p class=\"center\" style=\"text-align: center;\">[Al(H<sub>2<\/sub>O)<sub>4<\/sub>(OH)<sub>2<\/sub>]<sup>1+<\/sup>+ NaOH \u2194 Al(H<sub>2<\/sub>O)<sub>3<\/sub>(OH)<sub>3\u00a0<\/sub>+ OH<sup>1\u2013<\/sup><\/p>\n<p>Then a water of hydration from [Al(H<sub>2<\/sub>O)<sub>4<\/sub>(OH)<sub>2<\/sub>]<sup>1+\u00a0<\/sup>donates the hydrogen ion to become the third hydroxide ion it is acting as a Br\u00f8nsted-Lowry acid.<\/p>\n<p class=\"center\" style=\"text-align: center;\">[Al(H<sub>2<\/sub>O)<sub>4<\/sub>(OH)<sub>2<\/sub>]<sup>1+<\/sup> + HCl \u2194 [Al(H<sub>2<\/sub>O)<sub>5<\/sub>OH]<sup>2+<\/sup> + Cl<sup>1\u2013<\/sup><\/p>\n<p>When a hydroxide from [Al(H<sub>2<\/sub>O)<sub>4<\/sub>(OH)<sub>2<\/sub>]<sup>1+<\/sup> accepts\u00a0the hydrogen ion to create the fifth water of hydration it is acting as a Br\u00f8nsted-Lowry base.<\/p>\n<h3>Relative Strengths of Acids and Bases<\/h3>\n<p>Acids and bases can be <abbr title=\"The condition of a solution when the ratio of solute particles to solvent particles (or volume of solution) approaches saturation\">concentrated<\/abbr> or <abbr title=\"The condition of a solution when the ratio of solute particles to solvent particles (or volume of solution) is far from saturated\">dilute<\/abbr>, weak or strong. Do not confuse the\u00a0first two which describe the solution concentration, with the last two which describe the amount of\u00a0dissociation.<\/p>\n<ul>\n<li>A weak acid or base is one where only a small portion of the particles dissociate or one that\u00a0only partially ionizes.<\/li>\n<li>A strong acid or base is one that completely dissociates in water, or has 100% ionization.\u00a0Strong acids include: HCl, HBr, HI, HNO<sub>3<\/sub>, H<sub>2<\/sub>SO<sub>4<\/sub>, and\u00a0HClO<sub>4<\/sub>. All others are considered weak. Strong bases include: LiOH, NaOH, KOH,\u00a0Mg(OH)<sub>2<\/sub>, Ca(OH)<sub>2<\/sub>, Sr(OH)<sub>2<\/sub> and Ba(OH)<sub>2<\/sub>. All others\u00a0are considered weak.<\/li>\n<\/ul>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>Given that [H<sub>3<\/sub>O<sup>1+<\/sup>] = 1.0\u00d710<sup>-2 <\/sup>M at 25\u00b0C, what is the [OH<sup>1\u2013<\/sup> ]?<\/p>\n<ol>\n<li>1.0 \u00d710<sup>-2<\/sup> M<\/li>\n<li>1.0 \u00d710<sup>-5<\/sup> M<\/li>\n<li>1.0 \u00d710<sup>-7<\/sup> M<\/li>\n<li>1.0 \u00d710<sup>-12<\/sup> M<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is D. Using the equation: K<sub>w<\/sub> = [H<sub>3<\/sub>O<sup>1+<\/sup>][OH<sup>1\u2013<\/sup> ] = 1.0\u00d710<sup>-14<\/sup> M<sup>2<\/sup> and substituting the given concentration for [H<sub>3<\/sub>O<sup>1+ <\/sup>]:<\/p>\n<p class=\"q-reveal center\" style=\"text-align: center;\">[1.0\u00d710<sup>-2<\/sup> M][OH<sup>1\u2013<\/sup> ] = 1.0 \u00d710<sup>-14<\/sup> M<sup>2<\/sup><\/p>\n<p class=\"q-reveal center\"><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/Images\/chemistry\/img\/gaslaw\/s5_029.gif\" width=\"266\" height=\"46\" \/><\/p>\n<\/section>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>In the reaction CaO(<em>s<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) <img loading=\"lazy\" decoding=\"async\" class=\"non_block_image\" src=\"http:\/\/americanboard.org\/Subjects\/Images\/chemistry\/img\/gaslaw\/2sidedarrow.gif\" width=\"21\" height=\"14\" align=\"absmiddle\" \/>Ca(OH)<sub>2<\/sub>(<em>aq<\/em>)\u00a0calcium oxide acts as ________<\/p>\n<ol>\n<li>a Br\u00f8nsted-Lowry acid.<\/li>\n<li>a Br\u00f8nsted-Lowry base.<\/li>\n<li>an amphoteric substance.<\/li>\n<li>there is not enough information to answer this question<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is C. Calcium oxide accepts both hydrogen and a hydroxide from the water to\u00a0become calcium hydroxide.<\/p>\n<\/section>\n<\/section>\n<p><!-- CONTENT ENDS HERE --><\/p>\n<p><!-- UPDATE NEXT\/PREVIOUS BELOW --><\/p>\n<div class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/colligative-properties-and-related-laws\">\u2b05 Previous Lesson<\/a>\u00a0<a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/gas-laws-and-solutions\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/relationships-between-acids-bases-and-salts\">Next Lesson\u00a0\u27a1<\/a><\/div>\n<p><a class=\"backtotop\" href=\"#title\">Back to Top<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u2b05 Previous Lesson\u00a0Workshop Index\u00a0Next Lesson \u27a1 The Development and Theories of Acids and Bases Objective In this lesson we will examine three of the main theories used to define acids and bases, review the pH\u00a0scale, its applications, and its development, as well as identify acids and bases as strong or weak,\u00a0based on their dissociation. Previously [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-522","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages\/522","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/comments?post=522"}],"version-history":[{"count":7,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages\/522\/revisions"}],"predecessor-version":[{"id":944,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages\/522\/revisions\/944"}],"wp:attachment":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/media?parent=522"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}