{"id":237846,"date":"2025-06-17T17:15:36","date_gmt":"2025-06-17T17:15:36","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=237846"},"modified":"2025-06-17T17:15:38","modified_gmt":"2025-06-17T17:15:38","slug":"the-molarity-of-nitrous-acid-at-which-its-ph-becomes-2","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/17\/the-molarity-of-nitrous-acid-at-which-its-ph-becomes-2\/","title":{"rendered":"The molarity of nitrous acid at which its pH becomes 2"},"content":{"rendered":"\n<p>The molarity of nitrous acid at which its pH becomes 2<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-0-color\">The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n<p>To find the molarity of nitrous acid (HNO\u2082) when its pH is 2, we need to use its acid dissociation constant (Ka). Nitrous acid is a weak acid with a Ka of approximately 4.5 \u00d7 10\u207b\u2074.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><strong>Step 1: Use the pH to find the hydrogen ion concentration<\/strong><\/p>\n\n\n\n<p>pH = 2<\/p>\n\n\n\n<p>[H+]=10\u2212pH=10\u22122=0.01\u2009M[H\u207a] = 10^{\u2212pH} = 10^{\u22122} = 0.01 \\, \\text{M}[H+]=10\u2212pH=10\u22122=0.01M<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><strong>Step 2: Set up the ICE table for dissociation<\/strong><\/p>\n\n\n\n<p>Let the initial concentration of HNO\u2082 be <strong>C<\/strong> mol\/L. The dissociation equation is:<\/p>\n\n\n\n<p>HNO2\u21ccH++NO2\u2212\\text{HNO}_2 \\rightleftharpoons \\text{H}^+ + \\text{NO}_2^-HNO2\u200b\u21ccH++NO2\u2212\u200b<\/p>\n\n\n\n<p>At equilibrium:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>[HNO\u2082] = C &#8211; x<\/li>\n\n\n\n<li>[H\u207a] = x = 0.01<\/li>\n\n\n\n<li>[NO\u2082\u207b] = x = 0.01<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><strong>Step 3: Use the Ka expression<\/strong><\/p>\n\n\n\n<p>Ka=[H+][NO2\u2212][HNO2]Ka = \\frac{[H^+][NO_2^-]}{[HNO_2]}Ka=[HNO2\u200b][H+][NO2\u2212\u200b]\u200b<\/p>\n\n\n\n<p>Substitute known values:4.5\u00d710\u22124=(0.01)(0.01)C\u22120.014.5 \\times 10^{-4} = \\frac{(0.01)(0.01)}{C &#8211; 0.01}4.5\u00d710\u22124=C\u22120.01(0.01)(0.01)\u200b4.5\u00d710\u22124=1.0\u00d710\u22124C\u22120.014.5 \\times 10^{-4} = \\frac{1.0 \\times 10^{-4}}{C &#8211; 0.01}4.5\u00d710\u22124=C\u22120.011.0\u00d710\u22124\u200b<\/p>\n\n\n\n<p>Solve for C:C\u22120.01=1.0\u00d710\u221244.5\u00d710\u22124=0.222C &#8211; 0.01 = \\frac{1.0 \\times 10^{-4}}{4.5 \\times 10^{-4}} = 0.222C\u22120.01=4.5\u00d710\u221241.0\u00d710\u22124\u200b=0.222C=0.222+0.01=0.232\u2009MC = 0.222 + 0.01 = 0.232 \\, \\text{M}C=0.222+0.01=0.232M<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><strong>Answer: The molarity of nitrous acid is approximately 0.232 M when the pH is 2.<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Explanation )<\/h3>\n\n\n\n<p>To determine the molarity of nitrous acid (HNO\u2082) at which its pH becomes 2, we must understand how weak acids dissociate in water. Nitrous acid does not completely dissociate like strong acids. Instead, it partially ionizes and reaches an equilibrium. This means we can use its equilibrium constant (Ka) to find its concentration at a given pH.<\/p>\n\n\n\n<p>The pH is defined as the negative logarithm of the hydrogen ion concentration. A pH of 2 corresponds to a hydrogen ion concentration of 0.01 M. Since nitrous acid releases one proton (H\u207a) per molecule, this value also represents how much acid has dissociated into ions.<\/p>\n\n\n\n<p>We use an ICE table, which stands for Initial, Change, and Equilibrium, to organize the concentrations. Initially, we start with some unknown concentration C of HNO\u2082. As it dissociates, it produces H\u207a and NO\u2082\u207b ions. At equilibrium, we have 0.01 M of each of these ions and (C &#8211; 0.01) M of the undissociated acid.<\/p>\n\n\n\n<p>By substituting these into the Ka expression, we can solve for C. After rearranging and solving, we find that the molarity of nitrous acid is about 0.232 M.<\/p>\n\n\n\n<p>This approach illustrates how weak acid behavior is tied to both pH and the acid&#8217;s Ka. It also shows that we cannot simply assume a one-to-one correspondence between concentration and pH, as we could with strong acids. Instead, we need to consider the degree of dissociation and equilibrium conditions.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-925.jpeg\" alt=\"\" class=\"wp-image-237847\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>The molarity of nitrous acid at which its pH becomes 2 The Correct Answer and Explanation is: To find the molarity of nitrous acid (HNO\u2082) when its pH is 2, we need to use its acid dissociation constant (Ka). Nitrous acid is a weak acid with a Ka of approximately 4.5 \u00d7 10\u207b\u2074. Step 1: [&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-237846","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/237846","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=237846"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/237846\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=237846"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=237846"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=237846"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}