Name: __________________________________
Date: _________________
Period: _____
10 Homework: Isotopes and Atomic Mass
Fill in the blanks with the correct number of neutrons for each isotope?
Potassium-39 has ____ neutrons
Nickel-59 has ____ neutrons
Titanium-48 has ____ neutrons
Phosphorous-31 has ____ neutrons
Chromium-52 has ____ neutrons
Bromine-80 has ____ neutrons
Iodine-127 has ____ neutrons
Nitrogen-15 has ____ neutrons
Sodium-23 has ____ neutrons
Rutherfordium-261 has ____ neutrons
Write the name of the correct isotope for each of the combinations of protons and
neutrons below:
76 protons and 114 neutrons = ____________________________________
12 protons and 13 neutrons = ____________________________________
22 protons and 26 neutrons = ____________________________________
9 protons and 9 neutrons = ____________________________________
38 protons and 50 neutrons = ____________________________________
48 protons and 64 neutrons = ____________________________________
Determine the atomic mass of each element below. Show Work or receive NO CREDIT.
1. Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and
the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?
2. There are two primary isotopes found in any sample of copper: copper-63 and copper-65.
The isotope 65Cu composes 69.2% of the sample and 63Cu comprises the other 30.8%. Based on
this data, what is the atomic mass of copper?
3. An unknown element, X, is examined and three isotopes are determined to be present.
54X = 1.85%
55X = 35.26%
57X = 62.89%
What is the atomic mass of the unknown element X according to this data set?
4. An unknown element, A, is isolated and examined. It is determined that 55% of the sample is
composed of the isotope 125A, 26% of the sample is the isotope 127A, and the other 19% of the
sample is composed of 131A. Based on this information, what is the atomic mass of element A?
5. An unknown element, Z, is isolated and examined. It is determined that 82% of the sample is
composed of the isotope 88Z while the other 18% of the sample is composed of 90Z. Based on
this information, what is the atomic mass of element Z?
6. Uranium has three common isotopes. If the abundance of 234U is 0.01%, the abundance of
235U is 0.71%, and the abundance of 238U is 99.28%, what is the average atomic mass of
uranium?
7. A scientist collects data on a sample of gaseous neon. He determines that 90.5% of the
atoms in the sample are neon-20 and 9.50% of the atoms are neon-22. What would the atomic
mass of neon be based on this scientist’s data?
8. Titanium has five common isotopes: 46Ti (8.0%), 47Ti (7.8%), 48Ti (73.4%), 49Ti (5.5%), 50Ti
(5.3%). What is the average atomic mass of titanium?
9. Boron has two naturally occurring isotopes with masses of 10.0129 amu which occupies
19.91% and another isotope of 11.0093 amu and occupying 80.09%. What is the average
atomic mass of boron?
10. An unknown element, Z, is isolated and examined. It is determined that 67% of the sample
is composed of the isotope 89Z while the other 33% of the sample is composed of 91Z. Based on
this information, what is the atomic mass of element Z?
Mass times percentage plus mass times percentage
Plus mass times percentage plus mass times percent….