{"id":218667,"date":"2025-05-24T07:34:28","date_gmt":"2025-05-24T07:34:28","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=218667"},"modified":"2025-05-24T07:34:40","modified_gmt":"2025-05-24T07:34:40","slug":"when-observed-independently-which-of-the-following-are-indications-that-a-chemical-reaction-has-occurred","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/05\/24\/when-observed-independently-which-of-the-following-are-indications-that-a-chemical-reaction-has-occurred\/","title":{"rendered":"When observed independently, which of the following are indications that a chemical reaction has occurred"},"content":{"rendered":"\n

When observed independently, which of the following are indications that a chemical reaction has occurred? Select all that apply<\/p>\n\n\n\n

Melting of a solid
Evaporation of a liquid
Temperature change
Change in odor
Formation of a precipitate
Why does benzilic acid only precipitate in acidic solution and why does the pH need to be<\/p>\n\n\n\n

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

Part 1: Indications of a Chemical Reaction<\/h3>\n\n\n\n

Select all that apply:<\/strong><\/p>\n\n\n\n

\u2705 Temperature change<\/strong>
\u2705 Change in odor<\/strong>
\u2705 Formation of a precipitate<\/strong><\/p>\n\n\n\n

\u274c Melting of a solid<\/strong> \u2013 Physical change<\/em>
\u274c Evaporation of a liquid<\/strong> \u2013 Physical change<\/em><\/p>\n\n\n\n

\n\n\n\n

Part 2: Why Benzilic Acid Only Precipitates in Acidic Solution<\/h3>\n\n\n\n

Benzilic acid is a weak organic acid with a carboxylic acid functional group. Its solubility in water is highly dependent on the pH of the solution due to the acid-base equilibrium between its protonated (non-ionic) and deprotonated (ionic) forms.<\/p>\n\n\n\n

In basic or neutral solution<\/strong>, benzilic acid donates a proton from its carboxylic acid group, forming the benzilate anion<\/strong> (its conjugate base), which is more soluble in water<\/strong> due to its ionic nature. In this deprotonated state, benzilic acid exists as a water-soluble salt (e.g., sodium benzilate if NaOH was used), and does not precipitate.<\/p>\n\n\n\n

In acidic conditions<\/strong>, the concentration of hydrogen ions (H\u207a) in the solution increases, shifting the equilibrium toward the protonated (non-ionic) benzilic acid<\/strong>, which is less soluble<\/strong> in water. This reduced solubility causes the compound to precipitate out<\/strong> of solution as a solid. The precipitation is thus a result of the decreased ionic character and increased hydrophobicity of the molecule in its protonated form.<\/p>\n\n\n\n

The pH is critical<\/strong> because it determines the position of the acid-base equilibrium. To precipitate benzilic acid effectively, the solution must be acidic enough (typically pH < 5) to ensure most benzilic acid molecules are protonated. If the pH is too high (alkaline), the acid will remain in its ionic, soluble form and no precipitation will occur.<\/p>\n\n\n\n

In practical applications, adjusting the pH to acidic conditions is a common method for recovering weak acids from aqueous solution after a reaction or purification step. Therefore, careful pH control is essential for successful precipitation of benzilic acid.<\/p>\n\n\n\n

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

When observed independently, which of the following are indications that a chemical reaction has occurred? Select all that apply Melting of a solidEvaporation of a liquidTemperature changeChange in odorFormation of a precipitateWhy does benzilic acid only precipitate in acidic solution and why does the pH need to be The Correct Answer and Explanation is: Part […]<\/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-218667","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/218667","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=218667"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/218667\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=218667"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=218667"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=218667"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}