To calculate the pH of a solution of NH4Cl, we need to consider how NH4Cl behaves in water. Since NH4Cl is the salt of a weak base (NH3) and a strong acid (HCl), it will dissociate into NH4+ and Cl-. The NH4+ ion will act as a weak acid and undergo hydrolysis in water, releasing H+ ions and lowering the pH.<\/p>\n\n\n\n
Here\u2019s the breakdown of how to find the pH:<\/p>\n\n\n\n
- \n
- Hydrolysis Reaction of NH4+<\/strong>:
NH4+ + H2O \u21cc NH3 + H3O+ The NH4+ ion donates a proton to water, creating NH3 and hydronium ions (H3O+). The equilibrium constant for this reaction is the acid dissociation constant (Ka) for NH4+, which can be calculated from the given Kb for NH3.<\/li>\n\n\n\n- Relationship between Ka and Kb<\/strong>:
Since NH4+ is the conjugate acid of NH3, we can use the relationship: Ka=KwKbK_a = \\frac{K_w}{K_b}Ka\u200b=Kb\u200bKw\u200b\u200b where K_w is the ionization constant of water (1.0 \u00d7 10^-14 at 25\u00b0C), and Kb is the given value for NH3, which is 1.8 \u00d7 10^-5. Therefore, Ka=1.0\u00d710\u2212141.8\u00d710\u22125=5.56\u00d710\u221210K_a = \\frac{1.0 \\times 10^{-14}}{1.8 \\times 10^{-5}} = 5.56 \\times 10^{-10}Ka\u200b=1.8\u00d710\u221251.0\u00d710\u221214\u200b=5.56\u00d710\u221210<\/li>\n\n\n\n- Set up the ICE Table<\/strong>:
For the hydrolysis reaction, let the initial concentration of NH4+ be 0.035 M. Let x be the concentration of H3O+ (which is also equal to the concentration of NH3 produced). The equilibrium concentrations will be:\n- \n
- Initial: [NH4+] = 0.035 M, [H3O+] = 0, [NH3] = 0<\/li>\n\n\n\n
- Change: [NH4+] decreases by x, [H3O+] increases by x, [NH3] increases by x<\/li>\n\n\n\n
- Equilibrium: [NH4+] = 0.035 – x, [H3O+] = x, [NH3] = x<\/li>\n<\/ul>\n<\/li>\n\n\n\n
- Expression for Ka<\/strong>:
The Ka expression is: Ka=[NH3][H3O+][NH4+]=x\u22c5x0.035\u2212xK_a = \\frac{[NH3][H3O+]}{[NH4+]} = \\frac{x \\cdot x}{0.035 – x}Ka\u200b=[NH4+][NH3][H3O+]\u200b=0.035\u2212xx\u22c5x\u200b Since Ka is very small, we can approximate that 0.035 – x \u2248 0.035. So the equation simplifies to: 5.56\u00d710\u221210=x20.0355.56 \\times 10^{-10} = \\frac{x^2}{0.035}5.56\u00d710\u221210=0.035×2\u200b Solving for x: x2=(5.56\u00d710\u221210)\u22c50.035=1.946\u00d710\u221211x^2 = (5.56 \\times 10^{-10}) \\cdot 0.035 = 1.946 \\times 10^{-11}x2=(5.56\u00d710\u221210)\u22c50.035=1.946\u00d710\u221211 x=1.946\u00d710\u221211=1.4\u00d710\u22125\u2009Mx = \\sqrt{1.946 \\times 10^{-11}} = 1.4 \\times 10^{-5} \\, \\text{M}x=1.946\u00d710\u221211\u200b=1.4\u00d710\u22125M This is the concentration of H3O+ ions.<\/li>\n\n\n\n- Calculate pH<\/strong>:
pH is calculated using the formula: pH=\u2212log\u2061[H3O+]\\text{pH} = -\\log[H3O+]pH=\u2212log[H3O+] pH=\u2212log\u2061(1.4\u00d710\u22125)=4.85\\text{pH} = -\\log(1.4 \\times 10^{-5}) = 4.85pH=\u2212log(1.4\u00d710\u22125)=4.85<\/li>\n<\/ol>\n\n\n\nThus, the pH of the 0.035 M NH4Cl solution is approximately 4.85<\/strong>.<\/p>\n\n\n\n
This result indicates that the solution is slightly acidic, as expected from the hydrolysis of NH4+, the conjugate acid of a weak base.<\/p>\n\n\n\n
![\"\"](\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/07\/learnexams-banner8-360.jpeg\")
<\/figure>\n","protected":false},"excerpt":{"rendered":"NH4Cl is a weak base (Kb = 1.8 * 10^-5) in NH4Cl solution (0.035 M in NH4Cl) at 25\u00c2\u00b0C, and so the salt NH4Cl acts as a weak acid. What is the pH of a solution with NH4Cl? The Correct Answer and Explanation is: To calculate the pH of a solution of NH4Cl, we need […]<\/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-248970","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/248970","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=248970"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/248970\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=248970"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=248970"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=248970"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- Calculate pH<\/strong>:
- Relationship between Ka and Kb<\/strong>: