Name__________________________________Period_______Date_________
Calculating Atomic Mass
Calculating a Weighted Average
Directions: The table below shows average grades by category for John, a Chemistry
student. In MP1, John always “did” his homework (by copying off his friend’s paper,) but
didn’t bother reading the book (since it didn’t “count for a grade.”) In MP2, John decided
to start reading the book and doing his own homework, to see if it would make a
difference in his grades. Calculate John’s final grades for MP1 and MP2 to see if his
improved study habits made a difference.
Category
Homework/Classwork
Labs
Quizzes
Tests
Project
1.
Percent
of Grade
10
25
10
45
10
Average for
MP1
100
88
75
62
95
Average for
MP2
100
92
94
83
95
Calculate John’s final grade for MP1.
2. Calculate John’s final grade for MP2.
Calculating Average Atomic Mass
Directions: Use the information in the table below to answer questions 3 & 4.
Isotope
Silver-107
Silver-109
Mass (amu)
106.90509
108.90470
Percent Abundance
51.86
3. What would the percent abundance of Silver-109 be? Add it to the table.
4. Calculate the average atomic mass of an atom of Silver.
Directions: Use the information in the table below to answer questions 5 & 6.
Isotope
Silicon-28
Silicon-29
Silicon-30
Mass (amu)
27.98
28.98
29.97
Percent Abundance
92.21
4.70
3.09
5.
Look over the data, and estimate the value of the answer before you begin the
calculation. Will the weighted average be closer to 28, 29, or 30?
6.
Calculate the average atomic mass of an atom of Silicon.
Directions: Use the information in the table below to answer questions 7 & 8.
Isotope name
Iron-54
Iron-56
Iron-57
Iron-58
Percent Abundance
5.90
91.72
2.10
0.280
7.
Estimate the average atomic mass of Iron.
8.
Calculate the average atomic mass of Iron.
Mass (amu)
53.94
55.93
56.94
57.93
Directions: Samples of an unknown element X were collected and their masses were
recorded. Use the information presented in the data table to answer questions 9-13.
Isotope
Mass (amu)
1
37.765
Percent
Abundance
9.67
2
39.056
78.68
3
40.003
11.34
4
41.060
0.31
Mass Number
9. Fill in the mass number for each sample of element X in the data table.
10. What is the most common isotope of element X?
11. Calculate the average atomic mass of element X.
12. Using your periodic table, identify element X based on its average atomic mass.
What is the name of this element?
13. What is the atomic number of this element?