Chemistry 2202
Relative Atomic Mass Worksheet
Complete each of the following questions in the space provided.
1.
The element copper is found to contain the naturally occurring isotopes copper-63 with an atomic mass
of 62.93u and copper-65 with an atomic mass of 64.93u. The relative abundances are 69.1% and 30.9%
respectively. Calculate the average atomic mass of copper.
2.
Uranium has three isotopes with the following percent abundances and atomic masses:
234
235
0.0058%
U 0.71%
234.04u
235.04u
What is the average atomic mass of uranium?
U
3.
238
U
99.23%
238.05u
The four isotopes of lead are shown below, each with its percent by mass abundance, the composition of
its nucleus and atomic masses. Using this data, calculate the average atomic mass of lead.
82 p
122n
1.37%
203.97u
4.
Isotope
magnesium-24
magnesium-25
magnesium-26
82p
124n
26.26%
205.97u
atomic mass (u)
23.985
24.986
25.983
82p
125n
20.82%
206.98u
82p
126n
51.55%
207.97u
abundance (%)
78.99
10.00
11.0
5.
Isotope
Potassium-39
Potassium-40
Potassium-41
atomic mass (u)
38.964
39.964
40.962
abundance (%)
93.258
0.0117
6.73
6.
Isotope
Chromium-50
Chromium-52
Chromium-53
Chromium-54
atomic mass (u)
49.946
51.941
52.941
53.938
abundance (%)
4.345
83.789
9.501
2.365
Challenge Questions
Lithium has two naturally occurring isotopes. Lithium-6 has an atomic mass of 6.015 u; lithium-7 has an atomic
mass of 7.016 u. The average atomic mass of lithium is 6.941 u. What is the percentage of lithium-7 in nature?
Element X is composed of 4 naturally occurring isotopes. Based on the information, determine the average
atomic mass of the element and which element is X.
Isotope
Atomic mass (u)
Relative abundance (%)
A
31.97
94.93
B
32.97
0.76
C
33.97
4.29
D
35.97
0.02