Average Atomic Mass

An element has two naturally occurring isotopes. One is 10.013 amu and is 19.9% abundant. The other is 11.01 amu and is 80.1% abundant. What is the average atomic mass? What element is it?

• 9.012, Beryllium
• 12.011, Carbon
• 6.941, Lithium
• 10.812, Boron

Calculate the average atomic mass of this element.

• 106.38649amu
• 111.91896amu
• 107.8677amu
• 121

Compute the average atomic mass for this element.

• 27.977
• 28.09
• 28.976
• The average mass cannot be determined from provided information.

What is the mass number defined as?

• the number of protons
• the number of protons and neutrons
• the number of neutrons
• the number of protons and electrons

Atoms of the same element which have a different number of neutrons are called _________________.

• ions

• isotopes

• quarks

• molecules

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

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.

Four isotopes of lead include lead-204, lead-206, lead-207, and lead-208.  The average atomic mass of lead is 207.2.  Which isotope of lead is likely to be the most abundant.

• 204
• 206
• 207
• 208

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%

What do the heights of the peaks represent in the mass spectrum?

• number of isotopes
• relative abundance of each isotope
• average atomic mass
• charge:mass ratio