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Finding An Isotopic Mass

Finding An Isotopic Mass. A sample of boron consists of 10 B (mass 10.0 amu) and 11 B (mass 11.0 amu) If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?. Assign X and Y values: X = % 10 B Y = % 11 B Determine Y in terms of X

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Finding An Isotopic Mass

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  1. Finding An Isotopic Mass A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu) If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

  2. Assign X and Y values: X = % 10B Y = % 11B Determine Y in terms of X X + Y = 100 Y = 100 - X Solve for X: X (10.0) + (100 - X )(11.0) = 10.8 100 100 Multiply through by 100 10.0 X + 1100 - 11.0X = 1080

  3. Collect X terms 10.0 X - 11.0 X = 1080 - 1100 - 1.0 X = -20 X = -20 = 20 % 10B - 1.0 Y = 100 - X % 11B = 100 - 20% = 80% 11B

  4. Learning Check 8 Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass)

  5. Solution 8 2) 70% Solution 62.9X + 6490 = 64.9X = 6350 -2.0 X = -140 X = 70%

  6. Silver 107 106.91 • Silver 109 108.9 • Silver average amu 107.87 • What is the percentage abundance of each isotope

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