{"id":265201,"date":"2025-07-21T19:33:57","date_gmt":"2025-07-21T19:33:57","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=265201"},"modified":"2025-07-21T19:34:00","modified_gmt":"2025-07-21T19:34:00","slug":"calculate-the-formula-molar-mass-of-na2s2o3a%c2%b75h2o","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/07\/21\/calculate-the-formula-molar-mass-of-na2s2o3a%c2%b75h2o\/","title":{"rendered":"Calculate the formula (molar) mass of Na2S2O3\u00c2\u00b75H2O"},"content":{"rendered":"\n<p>Calculate the formula (molar) mass of Na2S2O3\u00c2\u00b75H2O. Part B: With the mass of KAl(SO4)2\u00c2\u00b712H2O crystal, calculate the number of moles<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-0-color\">The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n<p>Let&#8217;s calculate the molar mass of Na\u2082S\u2082O\u2083\u00b75H\u2082O and then solve for the number of moles in part B with the given mass of KAl(SO\u2084)\u2082\u00b712H\u2082O.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Part A: Molar Mass of Na\u2082S\u2082O\u2083\u00b75H\u2082O<\/h3>\n\n\n\n<p>The molar mass of a compound is the sum of the atomic masses of all the atoms in the formula. Here&#8217;s how to calculate it:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Na\u2082S\u2082O\u2083\u00b75H\u2082O<\/strong> consists of:\n<ul class=\"wp-block-list\">\n<li><strong>Sodium (Na)<\/strong>: The atomic mass of Na is 22.99 g\/mol. Since there are 2 Na atoms, the total mass is 2\u00d722.99=45.982 \\times 22.99 = 45.982\u00d722.99=45.98 g\/mol.<\/li>\n\n\n\n<li><strong>Sulfur (S)<\/strong>: The atomic mass of sulfur is 32.07 g\/mol. Since there are 2 sulfur atoms, the total mass is 2\u00d732.07=64.142 \\times 32.07 = 64.142\u00d732.07=64.14 g\/mol.<\/li>\n\n\n\n<li><strong>Oxygen (O)<\/strong>: The atomic mass of oxygen is 16.00 g\/mol. There are 3 oxygen atoms in the thiosulfate group (Na\u2082S\u2082O\u2083) and 5 oxygen atoms in the 5 water molecules. Thus, the total mass from oxygen is (3\u00d716.00)+(5\u00d716.00)=48.00+80.00=128.00(3 \\times 16.00) + (5 \\times 16.00) = 48.00 + 80.00 = 128.00(3\u00d716.00)+(5\u00d716.00)=48.00+80.00=128.00 g\/mol.<\/li>\n\n\n\n<li><strong>Hydrogen (H)<\/strong>: The atomic mass of hydrogen is 1.008 g\/mol. There are 10 hydrogen atoms from the 5 water molecules (since each H\u2082O molecule has 2 hydrogens). Thus, the total mass from hydrogen is 10\u00d71.008=10.0810 \\times 1.008 = 10.0810\u00d71.008=10.08 g\/mol.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p>Now, add all the masses together:Molar&nbsp;mass&nbsp;of&nbsp;Na\u2082S\u2082O\u2083\\cdotp5H\u2082O=45.98+64.14+128.00+10.08=248.20\u2009g\/mol\\text{Molar mass of Na\u2082S\u2082O\u2083\u00b75H\u2082O} = 45.98 + 64.14 + 128.00 + 10.08 = 248.20 \\, \\text{g\/mol}Molar&nbsp;mass&nbsp;of&nbsp;Na\u2082S\u2082O\u2083\\cdotp5H\u2082O=45.98+64.14+128.00+10.08=248.20g\/mol<\/p>\n\n\n\n<p>So, the molar mass of Na\u2082S\u2082O\u2083\u00b75H\u2082O is <strong>248.20 g\/mol<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Part B: Number of Moles of KAl(SO\u2084)\u2082\u00b712H\u2082O<\/h3>\n\n\n\n<p>To calculate the number of moles of KAl(SO\u2084)\u2082\u00b712H\u2082O, you need the mass of the crystal and the molar mass of KAl(SO\u2084)\u2082\u00b712H\u2082O.<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Find the molar mass of KAl(SO\u2084)\u2082\u00b712H\u2082O:<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Potassium (K)<\/strong>: Atomic mass = 39.10 g\/mol. There&#8217;s 1 K atom, so total = 39.10 g\/mol.<\/li>\n\n\n\n<li><strong>Aluminum (Al)<\/strong>: Atomic mass = 26.98 g\/mol. There&#8217;s 1 Al atom, so total = 26.98 g\/mol.<\/li>\n\n\n\n<li><strong>Sulfur (S)<\/strong>: Atomic mass = 32.07 g\/mol. There are 2 sulfate groups (SO\u2084), so total = 2\u00d732.07=64.142 \\times 32.07 = 64.142\u00d732.07=64.14 g\/mol.<\/li>\n\n\n\n<li><strong>Oxygen (O)<\/strong>: Atomic mass = 16.00 g\/mol. For sulfate (SO\u2084), there are 8 oxygen atoms, and for 12 water molecules, there are 24 oxygen atoms. Total oxygen = 8\u00d716.00+24\u00d716.00=128.00+384.00=512.008 \\times 16.00 + 24 \\times 16.00 = 128.00 + 384.00 = 512.008\u00d716.00+24\u00d716.00=128.00+384.00=512.00 g\/mol.<\/li>\n\n\n\n<li><strong>Hydrogen (H)<\/strong>: Atomic mass = 1.008 g\/mol. For 12 water molecules, there are 24 hydrogens. Total = 24\u00d71.008=24.1924 \\times 1.008 = 24.1924\u00d71.008=24.19 g\/mol.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<p>Now, adding these together:Molar&nbsp;mass&nbsp;of&nbsp;KAl(SO\u2084)\u2082\\cdotp12H\u2082O=39.10+26.98+64.14+512.00+24.19=666.41\u2009g\/mol\\text{Molar mass of KAl(SO\u2084)\u2082\u00b712H\u2082O} = 39.10 + 26.98 + 64.14 + 512.00 + 24.19 = 666.41 \\, \\text{g\/mol}Molar&nbsp;mass&nbsp;of&nbsp;KAl(SO\u2084)\u2082\\cdotp12H\u2082O=39.10+26.98+64.14+512.00+24.19=666.41g\/mol<\/p>\n\n\n\n<ol start=\"2\" class=\"wp-block-list\">\n<li><strong>Number of Moles<\/strong>:<br>To calculate the number of moles, use the formula:<\/li>\n<\/ol>\n\n\n\n<p>Number&nbsp;of&nbsp;moles=Mass&nbsp;of&nbsp;sampleMolar&nbsp;mass\\text{Number of moles} = \\frac{\\text{Mass of sample}}{\\text{Molar mass}}Number&nbsp;of&nbsp;moles=Molar&nbsp;massMass&nbsp;of&nbsp;sample\u200b<\/p>\n\n\n\n<p>So if you have a mass of KAl(SO\u2084)\u2082\u00b712H\u2082O, just plug it into the formula above. For example, if the sample weighs 50 grams, the number of moles would be:Number&nbsp;of&nbsp;moles=50.00\u2009g666.41\u2009g\/mol=0.075\u2009mol\\text{Number of moles} = \\frac{50.00 \\, \\text{g}}{666.41 \\, \\text{g\/mol}} = 0.075 \\, \\text{mol}Number&nbsp;of&nbsp;moles=666.41g\/mol50.00g\u200b=0.075mol<\/p>\n\n\n\n<p>Thus, the number of moles depends on the mass of the crystal you are working with.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/07\/learnexams-banner6-1434.jpeg\" alt=\"\" class=\"wp-image-265205\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the formula (molar) mass of Na2S2O3\u00c2\u00b75H2O. Part B: With the mass of KAl(SO4)2\u00c2\u00b712H2O crystal, calculate the number of moles The Correct Answer and Explanation is: Let&#8217;s calculate the molar mass of Na\u2082S\u2082O\u2083\u00b75H\u2082O and then solve for the number of moles in part B with the given mass of KAl(SO\u2084)\u2082\u00b712H\u2082O. Part A: Molar Mass of [&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-265201","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/265201","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=265201"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/265201\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=265201"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=265201"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=265201"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}