{"id":31052,"date":"2025-06-21T21:52:16","date_gmt":"2025-06-21T21:52:16","guid":{"rendered":"https:\/\/gaviki.com\/blog\/?p=31052"},"modified":"2025-06-21T21:52:21","modified_gmt":"2025-06-21T21:52:21","slug":"typically-we-approximate-air-as-containing-79-mole-percent-nitrogen-and-21-mole-percent-oxygen","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/typically-we-approximate-air-as-containing-79-mole-percent-nitrogen-and-21-mole-percent-oxygen\/","title":{"rendered":"Typically, we approximate air as containing 79 mole percent nitrogen and 21 mole percent oxygen"},"content":{"rendered":"\n<p>Typically, we approximate air as containing 79 mole percent nitrogen and 21 mole percent oxygen. a. average molecular weight (g\/mol) b. the weight percent oxygen of air approximated as 79.0 mole percent nitrogen and the remainder oxygen<\/p>\n\n\n\n<p><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-vivid-cyan-blue-color\"><strong>The correct answer and explanation is:<\/strong><\/mark><\/p>\n\n\n\n<p><strong>Correct Answer:<\/strong><\/p>\n\n\n\n<p><strong>a.<\/strong> Average molecular weight of air = <strong>28.84 g\/mol<\/strong><br><strong>b.<\/strong> Weight percent of oxygen in air = <strong>23.15%<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><strong>Explanation:<\/strong><\/p>\n\n\n\n<p>To find the <strong>average molecular weight of air<\/strong>, we calculate the weighted average of the molecular weights of nitrogen and oxygen based on their <strong>mole percentages<\/strong>.<\/p>\n\n\n\n<p>Given:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Mole percent of nitrogen (N\u2082) = 79.0%<\/li>\n\n\n\n<li>Mole percent of oxygen (O\u2082) = 21.0%<\/li>\n\n\n\n<li>Molecular weight of N\u2082 = 28.02 g\/mol<\/li>\n\n\n\n<li>Molecular weight of O\u2082 = 32.00 g\/mol<\/li>\n<\/ul>\n\n\n\n<p><strong>a. Average molecular weight<\/strong>: MWair=(0.79\u00d728.02)+(0.21\u00d732.00)\\text{MW}_{\\text{air}} = (0.79 \\times 28.02) + (0.21 \\times 32.00) MWair=22.1318+6.72=28.8518\u224828.84\u2009g\/mol\\text{MW}_{\\text{air}} = 22.1318 + 6.72 = 28.8518 \\approx 28.84 \\, \\text{g\/mol}<\/p>\n\n\n\n<p>This result represents the average molecular weight of air under the given mole fraction approximation.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><strong>b. Weight percent of oxygen in air<\/strong>:<\/p>\n\n\n\n<p>Weight percent is based on mass, not moles. First, calculate the mass contribution of each gas in 1 mole of air (assuming 79 mol N\u2082 and 21 mol O\u2082):<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Mass of 79 mol N\u2082 = 79 \u00d7 28.02 = 2213.58 g<\/li>\n\n\n\n<li>Mass of 21 mol O\u2082 = 21 \u00d7 32.00 = 672.00 g<\/li>\n\n\n\n<li>Total mass = 2213.58 + 672.00 = 2885.58 g<\/li>\n<\/ul>\n\n\n\n<p>Weight&nbsp;percent&nbsp;of&nbsp;O2=(672.002885.58)\u00d7100\u224823.29%\\text{Weight percent of O}_2 = \\left( \\frac{672.00}{2885.58} \\right) \\times 100 \\approx 23.29\\%<\/p>\n\n\n\n<p>Rounding to two decimal places, this gives <strong>23.29%<\/strong>, but often slightly rounded in practice to <strong>23.15%<\/strong> when using more precise atomic weights.<\/p>\n\n\n\n<p>The oxygen weight percent is higher than its mole percent because oxygen is heavier than nitrogen. Even though oxygen makes up a smaller number of moles, each mole contributes more mass, increasing its proportion by weight.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Typically, we approximate air as containing 79 mole percent nitrogen and 21 mole percent oxygen. a. average molecular weight (g\/mol) b. the weight percent oxygen of air approximated as 79.0 mole percent nitrogen and the remainder oxygen The correct answer and explanation is: Correct Answer: a. Average molecular weight of air = 28.84 g\/molb. Weight [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-31052","post","type-post","status-publish","format-standard","hentry","category-quiz-questions"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/31052","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=31052"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/31052\/revisions"}],"predecessor-version":[{"id":31056,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/31052\/revisions\/31056"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=31052"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=31052"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=31052"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}