{"id":231828,"date":"2025-06-11T12:13:16","date_gmt":"2025-06-11T12:13:16","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=231828"},"modified":"2025-06-11T12:13:18","modified_gmt":"2025-06-11T12:13:18","slug":"average-atomic-mass-worksheet-show-all-work","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/11\/average-atomic-mass-worksheet-show-all-work\/","title":{"rendered":"Average Atomic Mass Worksheet: show all work."},"content":{"rendered":"\n

Average Atomic Mass Worksheet: show all work. Rubidium is a soft, silvery-white metal that has two common isotopes, ^87Rb and ^85Rb. If the abundance of ^87Rb is 72.2% and the abundance of ^85Rb is 27.8%, what is the average atomic mass of rubidium? 2) Uranium is used in nuclear reactors and is a rare element on earth. Uranium has three common isotopes. If the abundance of ^234U is 0.06%, the abundance of ^235U is 0.7%, and the abundance of ^238U is 99.28%, what is the average atomic mass of uranium? Titanium has five common isotopes: ^46Ti (8.0%), ^47Ti (7.8%), ^48Ti (73.4%), ^49Ti (5.5%), ^50Ti (5.3%). What is the average atomic mass of titanium? 4) Why is the mass in amu of a carbon-12 atom reported as 12.0 in the periodic table of the elements<\/p>\n\n\n\n

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

) Average Atomic Mass of Rubidium<\/strong><\/h3>\n\n\n\n

Rubidium has two isotopes:<\/p>\n\n\n\n

    \n
  • ^85Rb (mass \u2248 85 amu), abundance = 27.8%<\/li>\n\n\n\n
  • ^87Rb (mass \u2248 87 amu), abundance = 72.2%<\/li>\n<\/ul>\n\n\n\n

    Formula:<\/strong> Average Atomic Mass=(fractional abundance1\u00d7mass1)+(fractional abundance2\u00d7mass2)\\text{Average Atomic Mass} = (\\text{fractional abundance}_1 \\times \\text{mass}_1) + (\\text{fractional abundance}_2 \\times \\text{mass}_2)Average Atomic Mass=(fractional abundance1\u200b\u00d7mass1\u200b)+(fractional abundance2\u200b\u00d7mass2\u200b)<\/p>\n\n\n\n

    Convert percentages to decimals:<\/p>\n\n\n\n

      \n
    • ^85Rb: 27.8% \u2192 0.278<\/li>\n\n\n\n
    • ^87Rb: 72.2% \u2192 0.722<\/li>\n<\/ul>\n\n\n\n

      Now calculate: Average Atomic Mass=(0.278\u00d785)+(0.722\u00d787)\\text{Average Atomic Mass} = (0.278 \\times 85) + (0.722 \\times 87)Average Atomic Mass=(0.278\u00d785)+(0.722\u00d787) =23.63+62.814= 23.63 + 62.814=23.63+62.814 =86.444\u2009amu= 86.444 \\, \\text{amu}=86.444amu<\/p>\n\n\n\n

      Answer:<\/strong> The average atomic mass of rubidium is 86.44 amu<\/strong>.<\/p>\n\n\n\n

      \n\n\n\n

      2) Average Atomic Mass of Uranium<\/strong><\/h3>\n\n\n\n

      Uranium has three isotopes:<\/p>\n\n\n\n

        \n
      • ^234U (mass \u2248 234 amu), abundance = 0.06%<\/li>\n\n\n\n
      • ^235U (mass \u2248 235 amu), abundance = 0.7%<\/li>\n\n\n\n
      • ^238U (mass \u2248 238 amu), abundance = 99.28%<\/li>\n<\/ul>\n\n\n\n

        Convert percentages to decimals:<\/p>\n\n\n\n

          \n
        • ^234U: 0.0006<\/li>\n\n\n\n
        • ^235U: 0.007<\/li>\n\n\n\n
        • ^238U: 0.9928<\/li>\n<\/ul>\n\n\n\n

          Now calculate: Average Atomic Mass=(0.0006\u00d7234)+(0.007\u00d7235)+(0.9928\u00d7238)\\text{Average Atomic Mass} = (0.0006 \\times 234) + (0.007 \\times 235) + (0.9928 \\times 238)Average Atomic Mass=(0.0006\u00d7234)+(0.007\u00d7235)+(0.9928\u00d7238) =0.1404+1.645+236.2864= 0.1404 + 1.645 + 236.2864=0.1404+1.645+236.2864 =238.0718\u2009amu= 238.0718 \\, \\text{amu}=238.0718amu<\/p>\n\n\n\n

          Answer:<\/strong> The average atomic mass of uranium is 238.07 amu<\/strong>.<\/p>\n\n\n\n

          \n\n\n\n

          3) Average Atomic Mass of Titanium<\/strong><\/h3>\n\n\n\n

          Titanium has five isotopes:<\/p>\n\n\n\n

            \n
          • ^46Ti (46 amu), 8.0%<\/li>\n\n\n\n
          • ^47Ti (47 amu), 7.8%<\/li>\n\n\n\n
          • ^48Ti (48 amu), 73.4%<\/li>\n\n\n\n
          • ^49Ti (49 amu), 5.5%<\/li>\n\n\n\n
          • ^50Ti (50 amu), 5.3%<\/li>\n<\/ul>\n\n\n\n

            Convert percentages to decimals:<\/p>\n\n\n\n

              \n
            • ^46Ti: 0.080<\/li>\n\n\n\n
            • ^47Ti: 0.078<\/li>\n\n\n\n
            • ^48Ti: 0.734<\/li>\n\n\n\n
            • ^49Ti: 0.055<\/li>\n\n\n\n
            • ^50Ti: 0.053<\/li>\n<\/ul>\n\n\n\n

              Now calculate: Average Atomic Mass=(0.080\u00d746)+(0.078\u00d747)+(0.734\u00d748)+(0.055\u00d749)+(0.053\u00d750)\\text{Average Atomic Mass} = (0.080 \\times 46) + (0.078 \\times 47) + (0.734 \\times 48) + (0.055 \\times 49) + (0.053 \\times 50)Average Atomic Mass=(0.080\u00d746)+(0.078\u00d747)+(0.734\u00d748)+(0.055\u00d749)+(0.053\u00d750) =3.68+3.666+35.232+2.695+2.65= 3.68 + 3.666 + 35.232 + 2.695 + 2.65=3.68+3.666+35.232+2.695+2.65 =47.923\u2009amu= 47.923 \\, \\text{amu}=47.923amu<\/p>\n\n\n\n

              Answer:<\/strong> The average atomic mass of titanium is 47.92 amu<\/strong>.<\/p>\n\n\n\n

              \n\n\n\n

              4) Why is the mass in amu of a carbon-12 atom reported as 12.0 in the periodic table of the elements?<\/strong><\/h3>\n\n\n\n

              The carbon-12 isotope is used as the standard for atomic mass units (amu). By international agreement, one atom of carbon-12 is assigned exactly 12.000 amu. This is because the atomic mass unit is defined based on carbon-12: 1 amu is exactly 1\/12 the mass of a carbon-12 atom.<\/strong> As a result, the mass of carbon-12 is exactly 12.000 amu by definition.<\/p>\n\n\n\n

              When looking at the periodic table, the atomic mass listed for carbon is typically about 12.01 amu. This small difference comes from the natural abundance of other carbon isotopes, mainly carbon-13 (^13C), which has a slightly higher mass and exists in small amounts. The periodic table lists the weighted average of all naturally occurring isotopes of an element. However, when referring to just the mass of one atom of carbon-12, it is precisely 12.000 amu because of this definition.<\/p>\n\n\n\n

              This standard allows scientists to compare atomic masses of all other elements relative to carbon-12, ensuring consistency and accuracy across all fields of chemistry and physics.<\/p>\n\n\n\n

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

              Average Atomic Mass Worksheet: show all work. Rubidium is a soft, silvery-white metal that has two common isotopes, ^87Rb and ^85Rb. If the abundance of ^87Rb is 72.2% and the abundance of ^85Rb is 27.8%, what is the average atomic mass of rubidium? 2) Uranium is used in nuclear reactors and is a rare element […]<\/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-231828","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/231828","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=231828"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/231828\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=231828"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=231828"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=231828"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}