calculating atomic mass and Isotopic abundance Flashcard Example #5728

atomic mass
average mass of all isotopes
atomic mass steps
1. multiply weights by percents (decimal form)
2. add those numbers
average atomic mass ex. av atomic mass of Ag107(106.9) and Ag 109 (108.9)with relative abundances of 51.8% and 48.2%
106.9 (0.518) + 108.9 ( 0.482)
= 107.9
isotopic abundance
abundance of isotope found naturally on earth
isotopic abundance steps
1. write first equation with weights multiplied by variables equal to average atomic mass

2. write second equation of percents equal to 1 (decimal form)

3. substitute and solve.

isotopic abundance ex. Si-28 , Si-29, and Si-29. the natural abundance of Si-29 is 4.67% find the other natural abundances. and average atomic mass is 28.
Si-30 = y
Si-28= x
Si-29 = 4.67%

1. 28x + 30y + 29(0.0467) = 28
2. x +y + 0.0467= 1
3. 28 (9533-y) +30y + 29 (0.0467) = 28

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