Average Atomic Mass & Relative Abundance

The atomic mass of an element is the ___.

• average of the mass number and the atomic number for the element

• weighted average of the masses of the isotopes of the element

• total mass of the isotopes of the element

• total number of subatomic particles in the nucleus

The atomic mass of an element depends upon the ___.

• relative abundance of protons in that element

• mass and relative abundance of each isotope of that element

• mass of each isotope of that element

• mass of each electron in that element

Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37, The atomic mass of chlorine is 35.45. Which of these two isotopes of chlorine is more abundant?

• Cl-35

• Cl-37

• Cannot be determined from the information provided.

The box for an element from the periodic table is shown. Which is the atomic mass?

• A

• B

• C

• D

An element has three isotopes. Given the abundances and relative masses, calculate the average atomic mass and determine (from the periodic table) which element it is.

Abundances | Relative masses

0.005% | 234.04 amu

0.720% | 235.04 amu

99.275% | 238.05 amu

• Uranium (#92, Atomic Mass: 238.03 amu)

• Fluorine (#9, Atomic Mass: 19.00 amu)

• Mercury (#89, Atomic Mass: 200.59 amu)

• Polonium (#84 209 amu)

Tags

NGSS.HS-PS1-8

Rubidium has two naturally occurring isotopes, ⁸⁵Rb (relative mass 84.9118 amu) and ⁸⁷Rb (relative mass 86.9092 amu). The abundance of ⁸⁷Rb is 27.8%, If rubidium has an average atomic mass of 85.47 amu, what is the % abundance of ⁸⁵Rb (in percent)?

• 27.9%

• 72.1%

• 74.63%

• 34.29%

Element Z has 2 natural isotopes. One isotope has a mass of 15.0 amu and a relative abundance of 30%. The other isotope has a mass of 16.0 amu and a relative abundance of 70%. Estimate the average atomic mass for this one element.

• 15.0 amu

• 16.0 amu

• 15.7 amu

• 16.9 amu

Tags

NGSS.MS-PS1-1

4.35% of all X atoms have a mass of 39.946 amu. 83.79% have a mass of 41.941 amu, 9.50% have a mass of 42.941 amu, and 2.36% have a mass of 43.939 amu. What is the average atomic mass of atom X?

• 41.97 amu
• 42.19 amu
• 10.43 amu
• 40.04 amu

Tags

NGSS.MS-PS1-1