Percent Abundance

Copper is made up of two isotopes, Cu-63 (62.9296 amu) and Cu-65 (64.9278 amu). Given copper's atomic weight of 63.546, what is the percent abundance of each isotope?

• Cu-63: 30.85% Cu-65: 69.15%

• Cu-63: 45.45% Cu-65: 54.55%

• Cu-63: 55.45% Cu-65: 44.55%

• Cu-63: 69.15% Cu-65: 30.85%

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

Calculate the average atomic mass of the element iron (Fe) using the following data:

[Isotope / % abundance]

[Iron 54 / 6% ] [Iron 56 / 92% ] [ Iron 57 / 2% ]

• 53.7 amu

• 54.9 amu

• 5592.0 amu

• 55.9 amu

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-PS1-1

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 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

A sample of chlorine consists of two isotopes: Cl-35 with a mass of 34.9689 amu and Cl-37 with a mass of 36.9659 amu. If the average atomic mass of chlorine is 35.453 amu, what is the percent abundance of Cl-35?

• A) 75.78%

• B) 24.22%

• C) 50.00%

• D) 70.00%

Gallium has two stable isotopes: Ga-69 with a mass of 68.9256 amu and Ga-71 with a mass of 70.9247 amu. If the average atomic mass of gallium is 69.723 amu, what is the percent abundance of Ga-69?

• A) 60.11%

• B) 39.89%

• C) 50.00%

• D) 70.00%