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Calculating Average Atomic Mass

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					Calculating Average
   Atomic Mass
Avg. Atomic Mass = Mass A (Abundance of A)
                   + Mass B (Abundance B) +…
Pg. 167. Q. 1-4
Calculating Isotopic Abundance
Same thing, just working backwards
through the equation
Example: Find the abundance of both boron-10
  (mass 10.01u) and boron-11 (mass 11.01u).
From periodic table, average atomic mass = 10.81u

Avg. Atomic Mass = MassA (Abun A) + MassB (AbunB)

10.81 = 10.01 (x) + 11.01 (1-x)
10.81 = 10.01x + 11.01-11.01x
10.81 = 10.01x + 11.01-11.01x
11.01x – 10.01x = 11.01 - 10.81
x = 0.2000
Therefore boron-10 is 20% and boron-11 is 80% abundant
Pg. 170, Q. 5-7

				
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