Calculating Average Atomic Mass Worksheet:
1) Three isotopes of Silicon occur in nature:
Isotopes of Silicon:
Percent Abundance:
Atomic Mass:
Silicon-28
92.23%
27.97693 amu
Silicon-29
4.68%
28.97649 amu
Silicon-30
3.09%
29.97377 amu
Calculate the average atomic mass for the three isotopes of Silicon.
(27.97693 x 0.9223) + (28.97649 x 0.0468) + (29.97377 x 0.0309)
Si-28
Si-29
Si-30
28.0854 am
2) Two isotopes of Rubidium occur naturally:
Isotopes of Rubidium:
Percent Abundance:
Atomic Mass:
Rubidium-85
72.15%
84.9118 amu
Rubidium-87
27.85%
86.9092 amu
Calculate the average atomic mass for the two isotopes of Rubidium.
(84.9118 x 0.7215) + (86.9092 x 0.2785)
Rubidium-85
Rubidium-87
85.468
3) Only two isotopes of Copper naturally occur:
Isotopes of Copper:
Percent Abundance:
Atomic Mass:
Copper-63
69.17%
62.9396 amu
Copper-65
30.83%
64.9278 amu
Calculate the average atomic mass for the two isotopes of Copper.
(62.9396 x 0.6917) + (64.9278 x 0.3083)
Copper-63
Copper-65
63.552
4) Chlorine has two naturally occurring isotopes:
Isotopes of Chlorine:
Percent Abundance:
Atomic Mass:
Chlorine-35
75.78%
34.969 amu
Chlorine-37
24.22%
36.966 amu
Calculate the average atomic mass for the two isotopes of Chlorine.
(34.969 x 0.7578) + (36.966 x 0.2422)
Chlorine-35
Chlorine-37
35.452
5) Two isotopes of Bromine naturally occur:
Isotopes of Bromine:
Percent Abundance:
Atomic Mass:
Bromine-79
50.69%
78.92 amu
Bromine-81
49.31%
80.92 amu
Calculate the average atomic mass for the two isotopes of Bromine.
(78.92 x 0.5069) + (80.92 x 0.4931)
Bromine-79
Bromine-81
79.906
6) Lead has four naturally occurring isotopes:
Isotopes of Lead:
Percent Abundance:
Lead-204
1.4%
Lead-206
24.1%
Lead-207
22.1%
Lead-208
52.4%
Calculate the average atomic mass for the four isotopes of Lead.
(204 x 0.014) + (206 x 0.241) + (207 x 0.221) + (208 x 0.524)
Lead-204
Lead-206
Lead-207
Lead-208
Atomic Mass:
204 amu
206 amu
207 amu
208 amu
207.241