{"id":225616,"date":"2025-06-04T10:48:48","date_gmt":"2025-06-04T10:48:48","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=225616"},"modified":"2025-06-04T10:48:50","modified_gmt":"2025-06-04T10:48:50","slug":"buffers","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/04\/buffers\/","title":{"rendered":"Buffers."},"content":{"rendered":"\n

Buffers. Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter of solution. [Ka(HCNO) = 2.0 \u00c3\u2014 10\u00e2\u20ac\u201c4]<\/p>\n\n\n\n

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

To calculate the pH of a buffer solution composed of a weak acid (cyanic acid, HCNO) and its conjugate base (cyanate ion, CNO\u207b, from sodium cyanate), we use the Henderson\u2013Hasselbalch equation<\/strong>: pH=pKa+log\u2061([A\u2212][HA])\\text{pH} = \\text{p}K_a + \\log \\left( \\frac{[\\text{A}^-]}{[\\text{HA}]} \\right)<\/p>\n\n\n\n

Step 1: Determine given values<\/h3>\n\n\n\n
    \n
  • Moles of HCNO (acid)<\/strong> = 0.20 mol<\/li>\n\n\n\n
  • Moles of NaCNO (conjugate base)<\/strong> = 0.80 mol<\/li>\n\n\n\n
  • Total volume<\/strong> = 1.0 L<\/li>\n\n\n\n
  • Therefore, concentrations:\n
      \n
    • [HCNO]=0.201.0=0.20\u2009M[HCNO] = \\frac{0.20}{1.0} = 0.20\\, \\text{M}<\/li>\n\n\n\n
    • [CNO\u2212]=0.801.0=0.80\u2009M[CNO^-] = \\frac{0.80}{1.0} = 0.80\\, \\text{M}<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n

      Step 2: Calculate pKa\\text{p}K_a<\/h3>\n\n\n\n

      Ka=2.0\u00d710\u22124\u21d2pKa=\u2212log\u2061(2.0\u00d710\u22124)\u22483.70K_a = 2.0 \\times 10^{-4} \\Rightarrow \\text{p}K_a = -\\log(2.0 \\times 10^{-4}) \\approx 3.70<\/p>\n\n\n\n

      Step 3: Use the Henderson\u2013Hasselbalch equation<\/h3>\n\n\n\n

      pH=3.70+log\u2061(0.800.20)\\text{pH} = 3.70 + \\log \\left( \\frac{0.80}{0.20} \\right) pH=3.70+log\u2061(4)\\text{pH} = 3.70 + \\log(4) pH=3.70+0.60=4.30\\text{pH} = 3.70 + 0.60 = 4.30<\/p>\n\n\n\n

      \n\n\n\n

      \u2705 Final Answer: pH = 4.30<\/strong><\/h3>\n\n\n\n
      \n\n\n\n

      Explanation<\/h3>\n\n\n\n

      Buffer solutions are critical in maintaining stable pH levels in chemical and biological systems. A buffer consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). When a small amount of acid or base is added to a buffer, it resists significant pH change due to the equilibrium between the acid and base components.<\/p>\n\n\n\n

      In this example, cyanic acid (HCNO) is a weak acid, and sodium cyanate (NaCNO) is its conjugate base in salt form. When NaCNO dissolves in water, it dissociates completely, releasing cyanate ions (CNO\u207b). These ions can react with any added H\u207a, while the HCNO can donate H\u207a to neutralize added OH\u207b\u2014providing buffering action.<\/p>\n\n\n\n

      The Henderson\u2013Hasselbalch equation is a convenient tool for calculating the pH of such buffer systems. It relates the pH to the acid dissociation constant (KaK_a) and the ratio of conjugate base to acid concentrations.<\/p>\n\n\n\n

      Here, with 0.80 mol of CNO\u207b and 0.20 mol of HCNO, the ratio [CNO\u2212][HCNO]\\frac{[\\text{CNO}^-]}{[\\text{HCNO}]} is 4. Taking the log of 4 gives 0.60. The KaK_a value provided for HCNO allows us to find its pKa\\text{p}K_a (3.70), and when we plug values into the Henderson\u2013Hasselbalch equation, the resulting pH is 4.30.<\/p>\n\n\n\n

      This pH value reflects a slightly acidic buffer (as expected, since HCNO is a weak acid), and the relatively high amount of conjugate base helps resist drops in pH, making this an effective buffer system.<\/p>\n\n\n\n

      \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

      Buffers. Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter of solution. [Ka(HCNO) = 2.0 \u00c3\u2014 10\u00e2\u20ac\u201c4] The Correct Answer and Explanation is: To calculate the pH of a buffer solution composed of a […]<\/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-225616","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/225616","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=225616"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/225616\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=225616"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=225616"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=225616"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}