Calculating Average Atomic Mass
Calculate the average atomic weight for the following: Show work on separate sheet of paper.
1. Isotope
Mg - 24
Mg - 25
Mg - 26
mass (amu)
23.985042
24.985837
25.982593
percent abundance
78.99%
10.00%
11.01%
2. Isotope
Silver-107
Silver-109
mass (amu)
106.90509
108.90470
percentage
51.86%
remainder
3. Isotope
Silicon-28
Silicon-29
Silicon-30
mass (amu)
27.98
28.98
29.97
Relative Abundance
92.21%
4.70%
3.09%
4. Isotope
234U
235U
238U
Percent Abundance (%)
00.0055%
0.720%
99.2745%
Mass (a.m.u.)
234.0409
235.0439
238.0508
5. Isotope Percent Abundance (%)
20Ne
90.92%
21Ne
0.26 %
22Ne
8.82 %
Mass (a.m.u.)
19.992
20.994
21.991
6. Isotope Percent Abundance (%)
32S
95.0 %
33S
0.76 %
34S
4.22 %
36S
0.014%
Mass (a.m.u.)
31.9757
32.9715
33.9679
35.9671
7. Isotope Percent Abundance (%)
46Ti
7.93
47Ti
7.28
48Ti
73.94
49Ti
5.51
50Ti
5.34
Mass (a.m.u.)
45.9526
46.9518
47.9480
48.9479
49.9448
8. Isotope
Iron-54
Iron-56
Iron-57
Iron-58
Isotope mass (amu)
53.94
55.93
56.94
57.93
Isotope abundance
5.90%
91.72%
2.10%
0.280%
9. Isotope
Mo - 92
Mo - 94
Mo - 95
Mo - 96
Mo - 97
Mo - 98
Mo - 100
mass(amu)
91.906808
93.905085
94.905840
95.904678
96.906020
97.905406
99.907477
percent abundance
14.84
9.25
15.92
16.68
9.55
24.13
9.63
10. The atomic mass of boron is 10.81 amu. Boron-10 occurs 80.1% of the time has an atomic
mass of 10.013 amu. Solve for the atomic mass of Boron-11 and the percent abundance
of Boron-11.
11. The atomic mass of copper is 63.546 amu. Copper-63 has an atomic mass of 62.9298,
and occurs 69.17% of the time. Solve for the atomic mass of copper-65 and its percent
abundance.
12. The atomic mass of lithium is 6.941 amu. The naturally occurring isotopes of lithium are
Lithium-6 and Lithium-7. Lithium-6 occurs 7.59% of the time and contains an atomic mass
of 6.015 amu. Solve for the percent abundance of lithium-7 and its atomic mass.
13. What is the molar mass of a natural sample of an element consists of three isotopes with
the following percentage abundances and molar masses?
% Abundance Molar Mass, g /mol
35.39
150.9377
35.25
151.9791
29.36
156.9332
14. What is the molar mass of the natural sample of Chlorine consists of three
isotopes with the following percentage abundances and molar masses.
% Abundance
75.77
24.23
Molar Mass, g /mol
34.9689
36.9659
15. What is the average molar mass of an iron nail that is composed of the
following four isotopes of Iron
% Abundance
5.80
91.72
2.20
0.280
Molar Mass, g /mol
53.9396
55.9349
56.9354
57.9333