{"id":231202,"date":"2025-06-10T15:42:08","date_gmt":"2025-06-10T15:42:08","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=231202"},"modified":"2025-06-10T15:42:10","modified_gmt":"2025-06-10T15:42:10","slug":"the-substance-benzoic-acid-c6h5cooh-is-a-weak-acid-ka-6-3a-10-5-2","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/10\/the-substance-benzoic-acid-c6h5cooh-is-a-weak-acid-ka-6-3a-10-5-2\/","title":{"rendered":"The substance benzoic acid (C6H5COOH) is a weak acid (Ka = 6.3\u00c3\u201410-5)."},"content":{"rendered":"\n

The substance benzoic acid (C6H5COOH) is a weak acid (Ka = 6.3\u00c3\u201410-5). What is the pH of a 0.232 M aqueous solution of sodium benzoate, NaC6H5COO? pH = This solution is (acidic, basic, or neutral.) b.) What is the pH of a 5.42\u00c3\u201410-2 M aqueous solution of potassium acetate, KCH3COO? pH = This solution is<\/em><\/strong> (acidic, basic, or neutral.) c.) What is the pH of a 7.90\u00c3\u201410-2 M aqueous solution of ammonium chloride, NH4Cl? pH = This solution is _<\/em><\/strong> (acidic, basic, or neutral.<\/p>\n\n\n\n

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

a.)<\/strong> The pH of a 0.232 M aqueous solution of sodium benzoate, NaC\u2086H\u2085COO, is:
pH = 8.78<\/strong>
This solution is basic<\/strong>.<\/p>\n\n\n\n

b.)<\/strong> The pH of a 5.42\u00d710\u207b\u00b2 M aqueous solution of potassium acetate, KCH\u2083COO, is:
pH = 8.74<\/strong>
This solution is basic<\/strong>.
(Note: This calculation uses the standard K\u2090 for acetic acid, 1.8\u00d710\u207b\u2075.)<\/em><\/p>\n\n\n\n

c.)<\/strong> The pH of a 7.90\u00d710\u207b\u00b2 M aqueous solution of ammonium chloride, NH\u2084Cl, is:
pH = 5.18<\/strong>
This solution is acidic<\/strong>.
(Note: This calculation uses the standard K\u2091 for ammonia, 1.8\u00d710\u207b\u2075.)<\/em><\/p>\n\n\n\n

\n\n\n\n

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

The pH of a salt solution is determined by the nature of the ions it forms upon dissolution in water. This process is known as salt hydrolysis<\/strong>. Salts formed from a strong acid and a strong base are neutral (pH = 7). However, when a salt contains an ion that is the conjugate acid of a weak base or the conjugate base of a weak acid, that ion will react with water to produce either hydronium ions (H\u2083O\u207a) or hydroxide ions (OH\u207b), thus altering the pH.<\/p>\n\n\n\n

In parts (a) and (b), sodium benzoate and potassium acetate are salts of a strong base (NaOH\/KOH) and a weak acid (benzoic acid\/acetic acid). The cation (Na\u207a\/K\u207a) is a spectator ion and does not affect the pH. The anion (C\u2086H\u2085COO\u207b\/CH\u2083COO\u207b), being the conjugate base of a weak acid, will accept a proton from water in an equilibrium reaction:<\/p>\n\n\n\n

A\u207b(aq) + H\u2082O(l) \u21cc HA(aq) + OH\u207b(aq)<\/p>\n\n\n\n

This production of hydroxide ions (OH\u207b) makes the solution basic (pH > 7). To find the pH, one must first calculate the base dissociation constant (K\u2091) for the anion using the relationship K\u2090 \u00d7 K\u2091 = K\u2092 (where K\u2092 = 1.0\u00d710\u207b\u00b9\u2074). An ICE (Initial, Change, Equilibrium) table is then used to determine the equilibrium concentration of OH\u207b, from which pOH is calculated (pOH = -log[OH\u207b]). Finally, the pH is found using the formula pH = 14.00 – pOH.<\/p>\n\n\n\n

In part (c), ammonium chloride is a salt of a weak base (NH\u2083) and a strong acid (HCl). The chloride ion (Cl\u207b) is a spectator ion. The ammonium ion (NH\u2084\u207a), the conjugate acid of a weak base, will donate a proton to water:<\/p>\n\n\n\n

BH\u207a(aq) + H\u2082O(l) \u21cc B(aq) + H\u2083O\u207a(aq)<\/p>\n\n\n\n

This production of hydronium ions (H\u2083O\u207a) makes the solution acidic (pH < 7). The acid dissociation constant (K\u2090) for the ammonium ion is calculated from the K\u2091 of ammonia (K\u2090 = K\u2092 \/ K\u2091). The equilibrium concentration of H\u2083O\u207a is then found, and the pH is calculated directly (pH = -log[H\u2083O\u207a]).<\/p>\n\n\n\n

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

The substance benzoic acid (C6H5COOH) is a weak acid (Ka = 6.3\u00c3\u201410-5). What is the pH of a 0.232 M aqueous solution of sodium benzoate, NaC6H5COO? pH = This solution is (acidic, basic, or neutral.) b.) What is the pH of a 5.42\u00c3\u201410-2 M aqueous solution of potassium acetate, KCH3COO? pH = This solution is […]<\/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-231202","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/231202","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=231202"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/231202\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=231202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=231202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=231202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}