{"id":117,"date":"2024-10-24T21:31:30","date_gmt":"2024-10-25T01:31:30","guid":{"rendered":"https:\/\/sites.temple.edu\/chemdemo\/?p=117"},"modified":"2024-10-25T16:22:01","modified_gmt":"2024-10-25T20:22:01","slug":"chemical-tests-for-aldehydes-ketones","status":"publish","type":"post","link":"https:\/\/sites.temple.edu\/chemdemo\/2024\/10\/24\/chemical-tests-for-aldehydes-ketones\/","title":{"rendered":"Chemical Tests for Aldehydes &amp; Ketones"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">Overview<\/h2>\n\n\n\n<p>This document outlines the procedures for 2 tests used to identify aldehydes and ketones:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>2,4-DNP Test<\/li>\n\n\n\n<li>Tollen&#8217;s Test<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\" \/>\n\n\n\n<h2 class=\"wp-block-heading\">2,4-DNP Test for Aldehydes and Ketones<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Standards<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Cyclohexanone<\/li>\n\n\n\n<li>Benzophenone<\/li>\n\n\n\n<li>Benzaldehyde<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Procedure<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Add a solution of 1 or 2 drops or 30 mg of the unknown compound in 2 mL of 95% ethanol to 3 mL of 2,4-dinitrophenylhydrazine reagent.<\/li>\n\n\n\n<li>Shake vigorously.<\/li>\n\n\n\n<li>If no precipitate forms immediately, allow the solution to stand for 15 minutes.<\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Note:<\/strong> The 2,4-dinitrophenylhydrazine reagent will already be prepared.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Positive Test<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Formation of a precipitate indicates a positive test.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Complications<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Some ketones yield oils that will not solidify.<\/li>\n\n\n\n<li>Some allylic alcohols may be oxidized by the reagent to aldehydes, resulting in a positive test.<\/li>\n\n\n\n<li>Unpurified alcohols may contain aldehyde or ketone impurities.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Tollen\u2019s Test for Aldehyde<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Standards<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Cyclohexanone<\/li>\n\n\n\n<li>Benzaldehyde<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Procedure<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Add one drop or a few crystals of the unknown to 1 mL of freshly prepared Tollens reagent.<\/li>\n\n\n\n<li>Gentle heating can be employed if no reaction is observed immediately.<\/li>\n<\/ol>\n\n\n\n<h4 class=\"wp-block-heading\">Tollens Reagent Preparation<\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Clean a test tube with 3M sodium hydroxide.<\/li>\n\n\n\n<li>Place 2 mL of 0.2 M silver nitrate solution in the test tube.<\/li>\n\n\n\n<li>Add a drop of 3M sodium hydroxide.<\/li>\n\n\n\n<li>Add 2.8% ammonia solution drop by drop, with constant shaking, until almost all silver oxide precipitate dissolves. Do not use more than 3 mL of ammonia.<\/li>\n\n\n\n<li>Dilute the entire solution to a final volume of 10 mL with water.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Positive Test<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Formation of a silver mirror or a black precipitate indicates a positive test.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Complications<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The test tube must be clean and oil-free for a silver mirror to be observed.<\/li>\n\n\n\n<li>Easily oxidized compounds (e.g., aromatic amines and some phenols) may yield false positives.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Cleaning Up<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Place all solutions used in this experiment in an appropriate waste container.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Overview This document outlines the procedures for 2 tests used to identify aldehydes and ketones: 2,4-DNP Test for Aldehydes and Ketones Standards Procedure Positive Test&#8230;<\/p>\n<div class=\"more-link-wrapper\"><a class=\"more-link\" href=\"https:\/\/sites.temple.edu\/chemdemo\/2024\/10\/24\/chemical-tests-for-aldehydes-ketones\/\">Continue Reading<span class=\"screen-reader-text\">Chemical Tests for Aldehydes &amp; Ketones<\/span><\/a><\/div>\n","protected":false},"author":36673,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-117","post","type-post","status-publish","format-standard","hentry","category-demonstrations","entry"],"_links":{"self":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/117","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/users\/36673"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/comments?post=117"}],"version-history":[{"count":1,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/117\/revisions"}],"predecessor-version":[{"id":118,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/117\/revisions\/118"}],"wp:attachment":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/media?parent=117"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/categories?post=117"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/tags?post=117"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}