{"id":211783,"date":"2025-06-16T08:37:11","date_gmt":"2025-06-16T08:37:11","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=211783"},"modified":"2025-06-16T08:37:13","modified_gmt":"2025-06-16T08:37:13","slug":"a-20-g-mixture-containing-95-by-weight-of-a-and-5-of-b-is-recrystallized-in-toluene-bp-110c","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/16\/a-20-g-mixture-containing-95-by-weight-of-a-and-5-of-b-is-recrystallized-in-toluene-bp-110c\/","title":{"rendered":"A 20 g mixture containing 95% (by weight) of A and 5% of B is recrystallized in toluene (bp: 110*C)."},"content":{"rendered":"\n<p>A 20 g mixture containing 95% (by weight) of A and 5% of B is recrystallized in toluene (bp: 110*C). Solubilities in g\/100 mL are given below: What amount of solvent is needed to obtain pure A and how much pure A will be recovered ? Show all calculations and explain your answers. Hint: the goal of a recrystallization is to keep ALL of the impurity dissolved at the low temperature: Knowing that; how much solvent is needed for this example? Temperature Solubility A 208 110&#8242; 1.5 g 10.0 g (g\/100 mL) 8.0 g 0.5 &amp; Question 4: Name the seven steps required for recrystallization of organic compounds?<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/06\/image-566.png\" alt=\"\" class=\"wp-image-236420\"\/><\/figure>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-6-color\">The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n<p><strong>Given:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Total mixture: 20 g<\/li>\n\n\n\n<li>A = 95% \u2192 0.95 \u00d7 20 = <strong>19 g<\/strong><\/li>\n\n\n\n<li>B = 5% \u2192 0.05 \u00d7 20 = <strong>1 g<\/strong><\/li>\n<\/ul>\n\n\n\n<p><strong>Goal:<\/strong> Recrystallize A and keep <em>all<\/em> of impurity B <strong>dissolved<\/strong> at <strong>low temperature<\/strong> (20\u00b0C).<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Step-by-step Calculation:<\/strong><\/h3>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Step 1: Use solubility of B at 20\u00b0C to calculate minimum solvent volume needed to keep all of B dissolved<\/strong><\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Solubility of B at 20\u00b0C = 0.5 g\/100 mL<\/li>\n\n\n\n<li>We need to dissolve 1.0 g of B, so:<\/li>\n<\/ul>\n\n\n\n<p>1.0\u2009g0.5\u2009g\/100\u2009mL=200\u2009mL&nbsp;of&nbsp;toluene\\frac{1.0 \\, g}{0.5 \\, g\/100 \\, mL} = 200 \\, \\text{mL of toluene}0.5g\/100mL1.0g\u200b=200mL&nbsp;of&nbsp;toluene<\/p>\n\n\n\n<p>\ud83d\udc49 <strong>Minimum 200 mL of solvent needed<\/strong> to keep <strong>all of B dissolved<\/strong> at 20\u00b0C.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Step 2: How much A remains dissolved at 20\u00b0C in 200 mL?<\/strong><\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Solubility of A at 20\u00b0C = 1.5 g\/100 mL<\/li>\n\n\n\n<li>In 200 mL:<\/li>\n<\/ul>\n\n\n\n<p>1.5\u2009g100\u2009mL\u00d7200\u2009mL=3.0\u2009g\\frac{1.5 \\, g}{100 \\, mL} \\times 200 \\, mL = 3.0 \\, g100mL1.5g\u200b\u00d7200mL=3.0g<\/p>\n\n\n\n<p>\ud83d\udc49 <strong>3 g of A will remain dissolved<\/strong> at 20\u00b0C and be <strong>lost<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Step 3: How much A is recovered?<\/strong><\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Initial A = 19 g<\/li>\n\n\n\n<li>Dissolved\/lost A = 3 g<\/li>\n<\/ul>\n\n\n\n<p>Recovered&nbsp;A=19\u2009g\u22123\u2009g=16\u2009g\\text{Recovered A} = 19 \\, g &#8211; 3 \\, g = \\boxed{16 \\, g}Recovered&nbsp;A=19g\u22123g=16g\u200b<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">\u2705 <strong>Final Answers:<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Amount of solvent needed:<\/strong> <strong>200 mL of toluene<\/strong><\/li>\n\n\n\n<li><strong>Amount of A recovered:<\/strong> <strong>16 g<\/strong><\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Question 4: Seven Steps of Recrystallization<\/strong><\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Choose a solvent<\/strong> \u2013 should dissolve compound when hot, not when cold.<\/li>\n\n\n\n<li><strong>Dissolve the solute<\/strong> \u2013 heat mixture in minimal hot solvent.<\/li>\n\n\n\n<li><strong>Decolorize the solution<\/strong> \u2013 (optional) add charcoal if colored impurities exist.<\/li>\n\n\n\n<li><strong>Filter the hot solution<\/strong> \u2013 remove insoluble impurities (hot gravity filtration).<\/li>\n\n\n\n<li><strong>Crystallize the solute<\/strong> \u2013 cool the filtrate slowly to form crystals.<\/li>\n\n\n\n<li><strong>Collect the crystals<\/strong> \u2013 use vacuum filtration to isolate solid.<\/li>\n\n\n\n<li><strong>Dry the product<\/strong> \u2013 remove any residual solvent to obtain pure compound.<\/li>\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/06\/image-567.png\" alt=\"\" class=\"wp-image-236424\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>A 20 g mixture containing 95% (by weight) of A and 5% of B is recrystallized in toluene (bp: 110*C). Solubilities in g\/100 mL are given below: What amount of solvent is needed to obtain pure A and how much pure A will be recovered ? Show all calculations and explain your answers. Hint: the [&hellip;]<\/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-211783","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/211783","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=211783"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/211783\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=211783"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=211783"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=211783"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}