1. What is the average atomic mass of carbon if it exists as 98.93% carbon-12 (atomic
mass = 12.0000 amu) and 1.07% carbon-13 (atomic mass = 13.0034 amu)?
2. A sample of sulfur contains 3 isotopes: sulfur-32 (94.93% abundance), sulfur-33
(0.76% abundance), and sulfur-34 (4.31% abundance). Calculate the average atomic
mass of sulfur.
3. Chlorine has two isotopes, chlorine-35 (atomic mass = 34.969 amu) and chlorine-37
(atomic mass = 36.966 amu). If the average atomic mass of chlorine is 35.453 amu,
what is the percent abundance of each isotope?
4. A sample of magnesium contains two isotopes, magnesium-24 (78.99% abundance)
and magnesium-25 (10.00% abundance). What is the atomic mass of the third
isotope if the average atomic mass of magnesium is 24.31 amu?
5. An element has three isotopes: isotope A with a mass of 31.00 amu and an
abundance of 15.00%, isotope B with a mass of 32.00 amu and an abundance of
80.00%, and isotope C with an unknown mass and an abundance of 5.00%. What is
the atomic mass of isotope C?
6. A sample of an element contains two isotopes: isotope X with a mass of 47.00 amu
and an abundance of 60.00%, and isotope Y with a mass of 49.00 amu and an
abundance of 40.00%. What is the percent abundance of isotope X in a sample of
this element with an average atomic mass of 47.60 amu?
7. Calculate the molecular weight of carbon dioxide (CO2).
8. What is the percent composition of hydrogen in water (H2O)?
9. Calculate the empirical formula of a compound that contains 56.5% carbon, 4.70%
hydrogen, and 38.8% oxygen by mass.
mass = 12.0000 amu) and 1.07% carbon-13 (atomic mass = 13.0034 amu)?
2. A sample of sulfur contains 3 isotopes: sulfur-32 (94.93% abundance), sulfur-33
(0.76% abundance), and sulfur-34 (4.31% abundance). Calculate the average atomic
mass of sulfur.
3. Chlorine has two isotopes, chlorine-35 (atomic mass = 34.969 amu) and chlorine-37
(atomic mass = 36.966 amu). If the average atomic mass of chlorine is 35.453 amu,
what is the percent abundance of each isotope?
4. A sample of magnesium contains two isotopes, magnesium-24 (78.99% abundance)
and magnesium-25 (10.00% abundance). What is the atomic mass of the third
isotope if the average atomic mass of magnesium is 24.31 amu?
5. An element has three isotopes: isotope A with a mass of 31.00 amu and an
abundance of 15.00%, isotope B with a mass of 32.00 amu and an abundance of
80.00%, and isotope C with an unknown mass and an abundance of 5.00%. What is
the atomic mass of isotope C?
6. A sample of an element contains two isotopes: isotope X with a mass of 47.00 amu
and an abundance of 60.00%, and isotope Y with a mass of 49.00 amu and an
abundance of 40.00%. What is the percent abundance of isotope X in a sample of
this element with an average atomic mass of 47.60 amu?
7. Calculate the molecular weight of carbon dioxide (CO2).
8. What is the percent composition of hydrogen in water (H2O)?
9. Calculate the empirical formula of a compound that contains 56.5% carbon, 4.70%
hydrogen, and 38.8% oxygen by mass.
