Average Atomic Mass

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

What is the average atomic mass for thallium, Tl, if there are two isotopes with the following masses and abundances? Tl-203 has a mass of 203 amu with an abundance of 29.5 % Tl-205 has a mass of 205 amu with an abundance of 70.5 %

• 203.12 amu

• 204.31 amu

• 204.41 amu

• 204.0 amu

A sample of cesium is 75% Cs-133, 20% Cs-132, and 5% Cs-134. What is the average atomic mass?

• 132.97 amu

• 133.00 amu

• 133.16 amu

• 132.85 amu

A meteor crashes to Earth, is collected and analyzed. To everyone’s surprise, a new element is discovered with an atomic number of 120. Calculate the weight-average atomic mass for this new element, Ubn (Unbinnulium). Show all work below.

• 315.250 amu

• 313.827 amu

• 313.333 amu

• 316.248 amu

Element Q is an unknown element. Q has abundance of 90.51%, Q has abundance of 0.21%, and Q has abundance of 9.22%. Find the average atomic mass of Q and identify the unknown element.

• F with mass = 19,894 amu

• Ne with mass = 20.17 amu

• Sodium with mass = 22.90 amu

• Mg with mass = 24.12 amu

An element with 4.35% have a mass of 49.9461 amu, 83.79% have amass of 51.9405 amu, 9.50% have a mass of 52.9407 amu, and 2.36% have a mass of 53.9389amu.

• 51.99 amu

• 52.19 amu

• 53.45 amu

• 17.33 amu

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

An element has two isotopes with masses of 10 amu and 11 amu. If the abundance of the 10 amu isotope is 20% and the 11 amu isotope is 80%, what is the average atomic mass of the element?

• 10.2 amu

• 10.8 amu

• 11.0 amu

• 10.5 amu

The average atomic mass of chlorine is 35.5 amu. If chlorine has two isotopes, Cl-35 and Cl-37, which isotope is more abundant?

• Cl-35

• Cl-37

• Both are equally abundant

• Cannot be determined

An element X has three isotopes with the following abundances and masses: 5% of 50 amu, 15% of 51 amu, and 80% of 52 amu. Calculate the average atomic mass of element X.

• 51.5 amu

• 51.8 amu

• 52.0 amu

• 51.0 amu