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Honors Chemistry – Unit 5 Worksheet 3
1. Element X has two natural isotopes. The isotope with a mass number of 6
has a relative abundance of 7.5%. The isotope with a mass number of 7 has a
relative abundance of 92.5%. Determine the average atomic mass for the
element from these figures. What is the true identity and atomic number of
element X? Write the nuclide notation for each isotope.
2. The element copper is found to contain the naturally occurring isotopes
29Cu63 and 29Cu65. The relative abundances are 69.1% and 30.9%
respectively. Calculate the average atomic mass of copper.
3. Uranium has three isotopes with the following percent abundances: 92U234
(0.0058%), 92U235 (0.71%), 92U238 (99.23%). Without doing a calculation,
what do you expect the atomic mass of uranium to be in whole numbers?
Why?
4. A sample of silver as it occurs in nature is 51.8% of isotope 47Ag107 and
48.2% of isotope 47Ag109. What is the average atomic mass of silver?
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U5 hon ws 3 2015
5. Ninety-two percent of the atoms of an element have a mass of 28.0 amu, 5.0%
of the atoms have a mass of 29.0 amu, and the remaining atoms have a mass
of 30.0 amu. Calculate the average atomic mass and identify the element.
Write the nuclide notation of each isotope.
6. Boron exists in two stable isotopes, boron-10 and boron-11. The average
atomic mass of boron is 10.80 amu. Calculate the relative abundance of each
isotope of boron. Write the nuclide notation of each isotope.
7. Antimony (Sb) exists in two stable isotopes, Sb-121 and Sb-123. From the
average atomic mass found on the Periodic Table, determine the relative
abundances of these two isotopes. Write the nuclide notation of each isotope.
8.
Iridium (Ir) exists in two stable isotopes, Ir-191 and Ir-193. From the
average atomic mass found on the Periodic Table, determine the relative
abundances of these two isotopes. Write the nuclide notation of each
isotope.
Modeling Chemistry
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U5 hon ws 3 2015