{"id":188390,"date":"2025-02-06T19:54:27","date_gmt":"2025-02-06T19:54:27","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=188390"},"modified":"2025-02-06T19:54:29","modified_gmt":"2025-02-06T19:54:29","slug":"citric-acid-h3c6h5o7-is-a-weak-triprotic-acid-with-pka1-3-13","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/02\/06\/citric-acid-h3c6h5o7-is-a-weak-triprotic-acid-with-pka1-3-13\/","title":{"rendered":"Citric acid (H3C6H5O7) is a weak triprotic acid with pKa1 = 3.13"},"content":{"rendered":"\n<p>Citric acid (H3C6H5O7) is a weak triprotic acid with pKa1 = 3.13, pKa2 = 4.77, and pKa3 = 6.40. Which of the following combinations of conjugate acid and base would be most appropriate as a buffer whose purpose is to maintain the pH around 5.8?<\/p>\n\n\n\n<p>A) Na2HC6H5O7 and Na3C6H5O7<\/p>\n\n\n\n<p>B) NaH2C6H5O7 and Na2HC6H5O7<\/p>\n\n\n\n<p>C) H3C6H5O7 and NaH2C6H5O7<\/p>\n\n\n\n<p>D) H3C6H5O7 and Na2HC6H5O7<\/p>\n\n\n\n<p>E) H3C6H5O7 and Na3C6H5O7<\/p>\n\n\n\n<p><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-6-color\"><strong>The Correct Answer and Explanation is :<\/strong><\/mark><\/p>\n\n\n\n<p>The correct answer is <strong>B) NaH2C6H5O7 and Na2HC6H5O7<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Explanation:<\/h3>\n\n\n\n<p>Citric acid (H\u2083C\u2086H\u2085O\u2087) is a triprotic weak acid with three dissociation steps, and its conjugate bases form a series of buffer pairs. To create a buffer solution with a pH around 5.8, we must choose a combination of an acid and its conjugate base that will allow us to maintain that pH. This can be determined by the pKa values of citric acid and the desired pH.<\/p>\n\n\n\n<p>The pKa values for citric acid are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>pKa1 = 3.13<\/li>\n\n\n\n<li>pKa2 = 4.77<\/li>\n\n\n\n<li>pKa3 = 6.40<\/li>\n<\/ul>\n\n\n\n<p>A buffer is most effective when the pH is close to the pKa of the weak acid in the buffer pair. The pH of 5.8 is closest to <strong>pKa2 (4.77)<\/strong>, indicating that the second dissociation step (from H\u2082C\u2086H\u2085O\u2087\u207b to HC\u2086H\u2085O\u2087\u00b2\u207b) is the most relevant for buffering around this pH.<\/p>\n\n\n\n<p>Looking at the options:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Option A: Na\u2082HC\u2086H\u2085O\u2087 and Na\u2083C\u2086H\u2085O\u2087<\/strong>: This pair is based on the second and third dissociation steps. The pKa3 (6.40) is higher than 5.8, so this pair would not be effective for buffering at this pH.<\/li>\n\n\n\n<li><strong>Option B: NaH\u2082C\u2086H\u2085O\u2087 and Na\u2082HC\u2086H\u2085O\u2087<\/strong>: This pair corresponds to the second dissociation step (pKa2 = 4.77), where H\u2082C\u2086H\u2085O\u2087\u207b is the acid and HC\u2086H\u2085O\u2087\u00b2\u207b is the base. This combination is appropriate for buffering near pH 5.8 because the pKa2 value is closest to the desired pH.<\/li>\n\n\n\n<li><strong>Option C: H\u2083C\u2086H\u2085O\u2087 and NaH\u2082C\u2086H\u2085O\u2087<\/strong>: This pair involves the first dissociation (pKa1 = 3.13), which is too low for a pH of 5.8.<\/li>\n\n\n\n<li><strong>Option D: H\u2083C\u2086H\u2085O\u2087 and Na\u2082HC\u2086H\u2085O\u2087<\/strong>: This pair is related to the first dissociation step, which is also not appropriate for a pH of 5.8.<\/li>\n\n\n\n<li><strong>Option E: H\u2083C\u2086H\u2085O\u2087 and Na\u2083C\u2086H\u2085O\u2087<\/strong>: This involves the first and third dissociation steps, both of which are not effective for buffering at pH 5.8.<\/li>\n<\/ul>\n\n\n\n<p>Thus, <strong>Option B (NaH\u2082C\u2086H\u2085O\u2087 and Na\u2082HC\u2086H\u2085O\u2087)<\/strong> is the most appropriate choice to buffer at a pH around 5.8.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Citric acid (H3C6H5O7) is a weak triprotic acid with pKa1 = 3.13, pKa2 = 4.77, and pKa3 = 6.40. Which of the following combinations of conjugate acid and base would be most appropriate as a buffer whose purpose is to maintain the pH around 5.8? A) Na2HC6H5O7 and Na3C6H5O7 B) NaH2C6H5O7 and Na2HC6H5O7 C) H3C6H5O7 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-188390","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/188390","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=188390"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/188390\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=188390"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=188390"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=188390"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}