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Oxygen is composed of three isotopes: One has a a mass of 16.999 amu. This isotope makes up 0.037% of oxygen. Of the other two, one has a mass of 15.995 amu, and the other has a mass of 17.999 amu. Calculate the abundance of the other two isotopes, using the average atomic mass of 15.9994 amu.

Answer» <html><body><p><a href="https://interviewquestions.tuteehub.com/tag/answer-15557" style="font-weight:bold;" target="_blank" title="Click to know more about ANSWER">ANSWER</a>: The <a href="https://interviewquestions.tuteehub.com/tag/abundance-846360" style="font-weight:bold;" target="_blank" title="Click to know more about ABUNDANCE">ABUNDANCE</a> in % for other two <a href="https://interviewquestions.tuteehub.com/tag/isotopes-1052577" style="font-weight:bold;" target="_blank" title="Click to know more about ISOTOPES">ISOTOPES</a> of the oxygen is 99.762% and 0.201%</p><p></p><p>Explanation :</p><p></p><p>The average atomic mass of an <a href="https://interviewquestions.tuteehub.com/tag/element-969236" style="font-weight:bold;" target="_blank" title="Click to know more about ELEMENT">ELEMENT</a> is the total of isotopic mass times the percent abundance for all the isotopes.</p><p></p><p>Oxygen has <a href="https://interviewquestions.tuteehub.com/tag/3-301577" style="font-weight:bold;" target="_blank" title="Click to know more about 3">3</a> isotope, 160, '70 and 180.</p><p></p><p>The average atomic mass of oxygen can be calculated as follows.</p><p></p><p>Average Atomic Mass = (Isotopic mass of 160 x % abundance of 160) + (isotopic mass of "0 x % abundance of "O) + (Isotopic mass of 180 x % abundance of 180)</p><p></p><p>17 The mass of "O = 16.999 amu and its % abundance is 0.037% which is 0.00037</p><p></p><p>The mass of 160 = 15.995 amu. Let us assume its % abundance as a</p><p></p><p>The mass of 180 = 17.999 amu</p><p></p><p>The total % abundance for all the isotopes is 100% or 1.</p><p></p><p>Therefore % abundance for 180 would be 1- (a + 0.00037) = 0.99963 a =</p><p></p><p>Let us plug in the above values in the average atomic mass formula.</p><p></p><p>Average atomic mass = ( 15.995)(a) + = (16.999)(0.00037) + (17.999)(0.99963 - a)</p><p></p><p>The average atomic mass of element O is 15.9994</p><p></p><p>Therefore we have,</p><p></p><p>15.9994 = 15.995a + 0.0062896 + 17.99234 - 17.999a</p><p></p><p>15.9994 = -2.004a + 17.99863</p><p></p><p>-1.99923 = -2.004a</p><p></p><p>a = 0.99762</p><p></p><p>a = 99.762%</p><p></p><p>The percent abundance of 16 O is</p><p></p><p>99.762%</p><p></p><p>The percent abundance of 180 is 0.99963 - 0.99762 = 0.00201 or 0.201%</p><p></p><p>50.</p></body></html>


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