{"id":217980,"date":"2025-05-22T21:07:31","date_gmt":"2025-05-22T21:07:31","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=217980"},"modified":"2025-05-22T21:07:33","modified_gmt":"2025-05-22T21:07:33","slug":"predict-the-pka-value-for-h2so4-hso4-and-so4-2","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/05\/22\/predict-the-pka-value-for-h2so4-hso4-and-so4-2\/","title":{"rendered":"Predict the pKa value for H2SO4, HSO4 \u2013 and SO4 2"},"content":{"rendered":"\n

Predict the pKa value for H2SO4, HSO4 \u2013 and SO4 2\u2013.<\/p>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

Correct Answer:<\/strong><\/h3>\n\n\n\n
    \n
  • H\u2082SO\u2084 (sulfuric acid):<\/strong> pKa\u2081 \u2248 \u20133<\/strong><\/li>\n\n\n\n
  • HSO\u2084\u207b (hydrogen sulfate ion):<\/strong> pKa\u2082 \u2248 1.99<\/strong><\/li>\n\n\n\n
  • SO\u2084\u00b2\u207b (sulfate ion):<\/strong> Does not have a relevant pKa<\/strong> (very weakly basic, conjugate base of a strong acid)<\/li>\n<\/ul>\n\n\n\n
    \n\n\n\n

    Explanation (300+ words):<\/strong><\/h3>\n\n\n\n

    Sulfuric acid (H\u2082SO\u2084)<\/strong> is a diprotic strong acid<\/strong>, meaning it can donate two protons (H\u207a) in solution. The acidity of a molecule is quantified using pKa<\/strong>, the negative base-10 logarithm of the acid dissociation constant (Ka). Lower pKa values indicate stronger acids.<\/p>\n\n\n\n

      \n
    1. First dissociation:<\/strong> $$
      \\text{H\u2082SO\u2084} \\rightarrow \\text{H\u207a} + \\text{HSO\u2084\u207b}
      $$ The first proton<\/strong> of H\u2082SO\u2084 dissociates completely<\/strong> in aqueous solution. This is why H\u2082SO\u2084 is classified as a strong acid<\/strong>. Since this dissociation is virtually 100%, the corresponding pKa is very low<\/strong>, typically estimated to be around \u20133<\/strong>. Such a low pKa indicates that H\u2082SO\u2084 readily donates its first proton, leaving behind the hydrogen sulfate ion (HSO\u2084\u207b).<\/li>\n\n\n\n
    2. Second dissociation:<\/strong> $$
      \\text{HSO\u2084\u207b} \\rightleftharpoons \\text{H\u207a} + \\text{SO\u2084\u00b2\u207b}
      $$ The second proton<\/strong> is not lost as easily, making HSO\u2084\u207b a weak acid<\/strong>. Its pKa value is approximately 1.99<\/strong>, meaning it only partially dissociates in solution. This value indicates that HSO\u2084\u207b is still acidic, but significantly weaker than H\u2082SO\u2084 itself.<\/li>\n\n\n\n
    3. SO\u2084\u00b2\u207b (sulfate ion):<\/strong>
      The sulfate ion<\/strong> is the conjugate base of HSO\u2084\u207b. Since HSO\u2084\u207b has a relatively low pKa (~2), its conjugate base (SO\u2084\u00b2\u207b) is very weakly basic<\/strong> and does not act as an acid<\/strong> under normal conditions. Therefore, it does not have a meaningful pKa<\/strong>, as it is not likely to donate a proton further.<\/li>\n<\/ol>\n\n\n\n

      Summary:<\/h3>\n\n\n\n
        \n
      • H\u2082SO\u2084: pKa\u2081 \u2248 \u20133<\/strong> (strong acid)<\/li>\n\n\n\n
      • HSO\u2084\u207b: pKa\u2082 \u2248 1.99<\/strong> (weak acid)<\/li>\n\n\n\n
      • SO\u2084\u00b2\u207b: No relevant pKa (conjugate base of a weak aci<\/li>\n<\/ul>\n\n\n\n
        \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

        Predict the pKa value for H2SO4, HSO4 \u2013 and SO4 2\u2013. The Correct Answer and Explanation is: Correct Answer: Explanation (300+ words): Sulfuric acid (H\u2082SO\u2084) is a diprotic strong acid, meaning it can donate two protons (H\u207a) in solution. The acidity of a molecule is quantified using pKa, the negative base-10 logarithm of the acid […]<\/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-217980","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/217980","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=217980"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/217980\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=217980"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=217980"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=217980"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}