{"id":222360,"date":"2025-05-31T09:16:46","date_gmt":"2025-05-31T09:16:46","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=222360"},"modified":"2025-05-31T09:16:48","modified_gmt":"2025-05-31T09:16:48","slug":"an-aqueous-buffer-solution-contains-only-hcn-pk-9-31-and-kcn-and-has-a-ph-of-8-50","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/05\/31\/an-aqueous-buffer-solution-contains-only-hcn-pk-9-31-and-kcn-and-has-a-ph-of-8-50\/","title":{"rendered":"An aqueous buffer solution contains only HCN (PK, = 9.31) and KCN and has a pH of 8.50."},"content":{"rendered":"\n<p>An aqueous buffer solution contains only HCN (PK, = 9.31) and KCN and has a pH of 8.50. What can be concluded about the relative concentrations of HCN and KCN in the buffer?<br>(A) [HCN]&gt; [KCN]<br>(B) [HCN]&lt; [kcn]=&#8221;&#8221;&gt;<br>(C) [HCM] = [KCN]<br>(D) nothing can be concluded about the relative concentrations<\/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><strong>Correct Answer: (A) [HCN] &gt; [KCN]<\/strong><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Explanation:<\/h3>\n\n\n\n<p>The given buffer solution contains hydrogen cyanide (HCN), a weak acid, and potassium cyanide (KCN), its conjugate base. KCN dissociates completely in water to form CN\u207b, the conjugate base of HCN.<\/p>\n\n\n\n<p>To analyze the relative concentrations of HCN and CN\u207b (from KCN), we use the <strong>Henderson-Hasselbalch equation<\/strong>: pH=pKa+log\u2061([Base][Acid])\\text{pH} = \\text{p}K_a + \\log\\left(\\frac{[\\text{Base}]}{[\\text{Acid}]}\\right)<\/p>\n\n\n\n<p>Here:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>pH<\/strong> = 8.50 (given)<\/li>\n\n\n\n<li><strong>pK\u2090<\/strong> = 9.31 (for HCN)<\/li>\n\n\n\n<li>Base = CN\u207b (from KCN)<\/li>\n\n\n\n<li>Acid = HCN<\/li>\n<\/ul>\n\n\n\n<p>Substituting into the equation: 8.50=9.31+log\u2061([CN\u2212][HCN])8.50 = 9.31 + \\log\\left(\\frac{[\\text{CN}^-]}{[\\text{HCN}]}\\right)<\/p>\n\n\n\n<p>Solving for the log term: log\u2061([CN\u2212][HCN])=8.50\u22129.31=\u22120.81\\log\\left(\\frac{[\\text{CN}^-]}{[\\text{HCN}]}\\right) = 8.50 &#8211; 9.31 = -0.81<\/p>\n\n\n\n<p>Now convert the log value: [CN\u2212][HCN]=10\u22120.81\u22480.155\\frac{[\\text{CN}^-]}{[\\text{HCN}]} = 10^{-0.81} \\approx 0.155<\/p>\n\n\n\n<p>This means: [CN\u2212]&lt;[HCN][\\text{CN}^-] &lt; [\\text{HCN}]<\/p>\n\n\n\n<p>Since CN\u207b comes from <strong>KCN<\/strong>, we can conclude that <strong>[KCN] &lt; [HCN]<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Conclusion:<\/h3>\n\n\n\n<p>In the buffer, the pH (8.50) is lower than the pK\u2090 (9.31), which means the solution is more acidic than the point at which equal concentrations of acid and base would occur. Therefore, the concentration of the acid (HCN) must be greater than the concentration of the base (CN\u207b from KCN).<\/p>\n\n\n\n<p>Thus, the correct answer is <strong>(A) [HCN] > [KCN]<\/strong>.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/05\/learnexams-banner7-158.jpeg\" alt=\"\" class=\"wp-image-222361\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>An aqueous buffer solution contains only HCN (PK, = 9.31) and KCN and has a pH of 8.50. What can be concluded about the relative concentrations of HCN and KCN in the buffer?(A) [HCN]&gt; [KCN](B) [HCN]&lt; [kcn]=&#8221;&#8221;&gt;(C) [HCM] = [KCN](D) nothing can be concluded about the relative concentrations The Correct Answer and Explanation is: Correct [&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-222360","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/222360","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=222360"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/222360\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=222360"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=222360"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=222360"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}