{"id":36663,"date":"2025-06-25T08:37:59","date_gmt":"2025-06-25T08:37:59","guid":{"rendered":"https:\/\/gaviki.com\/blog\/?p=36663"},"modified":"2025-06-25T08:38:01","modified_gmt":"2025-06-25T08:38:01","slug":"nitrous-acid-hno2-is-a-weak-acid-with-a-pka-of-3-14","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/nitrous-acid-hno2-is-a-weak-acid-with-a-pka-of-3-14\/","title":{"rendered":"Nitrous acid, HNO2, is a weak acid with a pKa of 3.14."},"content":{"rendered":"\n<p>Nitrous acid, HNO2, is a weak acid with a pKa of 3.14. What is the predominant form present in a solution with a pH of 5.00? Write the chemical formula, not just the word acid or base.<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-vivid-cyan-blue-color\">The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Correct Answer:<\/strong><\/h3>\n\n\n\n<p>The predominant form is <strong>NO\u2082\u207b<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Explanation:<\/strong><\/h3>\n\n\n\n<p>Nitrous acid (<strong>HNO\u2082<\/strong>) is a <strong>weak acid<\/strong>, meaning it only partially dissociates in water. The equilibrium reaction for nitrous acid in water is:HNO2\u2005\u200a\u21cc\u2005\u200aH+\u2005\u200a+\u2005\u200aNO2\u2212\\text{HNO}_2 \\; \\rightleftharpoons \\; \\text{H}^+ \\; + \\; \\text{NO}_2^-HNO2\u200b\u21ccH++NO2\u2212\u200b<\/p>\n\n\n\n<p>To determine the predominant form at a given pH, we compare the solution\u2019s pH to the acid\u2019s <strong>pKa<\/strong>, which is <strong>3.14<\/strong> for HNO\u2082.<\/p>\n\n\n\n<p>The <strong>pKa<\/strong> is the pH at which the concentrations of the acid form (<strong>HNO\u2082<\/strong>) and its conjugate base (<strong>NO\u2082\u207b<\/strong>) are equal. If the pH is:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Lower than the pKa<\/strong>, the <strong>acid form (HNO\u2082)<\/strong> is more prevalent.<\/li>\n\n\n\n<li><strong>Higher than the pKa<\/strong>, the <strong>base form (NO\u2082\u207b)<\/strong> is more prevalent.<\/li>\n<\/ul>\n\n\n\n<p>In this problem, the <strong>pH is 5.00<\/strong>, which is significantly <strong>higher than the pKa of 3.14<\/strong>. This means the environment is more <strong>basic<\/strong>, and the equilibrium shifts toward the deprotonated form \u2014 the <strong>conjugate base<\/strong>, NO\u2082\u207b.<\/p>\n\n\n\n<p>We can also use the <strong>Henderson-Hasselbalch equation<\/strong> to reinforce our conclusion:pH=pKa+log\u2061([NO2\u2212][HNO2])\\text{pH} = \\text{pKa} + \\log\\left(\\frac{[\\text{NO}_2^-]}{[\\text{HNO}_2]}\\right)pH=pKa+log([HNO2\u200b][NO2\u2212\u200b]\u200b)<\/p>\n\n\n\n<p>Plugging in the values:5.00=3.14+log\u2061([NO2\u2212][HNO2])5.00 = 3.14 + \\log\\left(\\frac{[\\text{NO}_2^-]}{[\\text{HNO}_2]}\\right)5.00=3.14+log([HNO2\u200b][NO2\u2212\u200b]\u200b)log\u2061([NO2\u2212][HNO2])=1.86\\log\\left(\\frac{[\\text{NO}_2^-]}{[\\text{HNO}_2]}\\right) = 1.86log([HNO2\u200b][NO2\u2212\u200b]\u200b)=1.86[NO2\u2212][HNO2]\u2248101.86\u224872.4\\frac{[\\text{NO}_2^-]}{[\\text{HNO}_2]} \\approx 10^{1.86} \\approx 72.4[HNO2\u200b][NO2\u2212\u200b]\u200b\u2248101.86\u224872.4<\/p>\n\n\n\n<p>This shows that the concentration of NO\u2082\u207b is about <strong>72 times higher<\/strong> than HNO\u2082 at pH 5.00.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Conclusion:<\/strong><\/h3>\n\n\n\n<p>Since the conjugate base <strong>NO\u2082\u207b<\/strong> is present in much higher concentration, <strong>NO\u2082\u207b is the predominant form<\/strong> in a solution of pH 5.00.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"852\" height=\"1024\" src=\"https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-812.jpeg\" alt=\"\" class=\"wp-image-36671\" srcset=\"https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-812.jpeg 852w, https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-812-250x300.jpeg 250w, https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-812-768x923.jpeg 768w\" sizes=\"auto, (max-width: 852px) 100vw, 852px\" \/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Nitrous acid, HNO2, is a weak acid with a pKa of 3.14. What is the predominant form present in a solution with a pH of 5.00? Write the chemical formula, not just the word acid or base. The Correct Answer and Explanation is: Correct Answer: The predominant form is NO\u2082\u207b. Explanation: Nitrous acid (HNO\u2082) is [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-36663","post","type-post","status-publish","format-standard","hentry","category-quiz-questions"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/36663","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=36663"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/36663\/revisions"}],"predecessor-version":[{"id":36672,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/36663\/revisions\/36672"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=36663"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=36663"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=36663"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}