Average Atomic Mass Concept and Calculations

Which of the following represents isotopes of the same element?

• ₈¹⁸O and ₇¹⁸O

• ₉¹⁹F and ₁₀¹⁹Ne

• ₉¹⁹F and ₉¹⁹Ne

• ₈¹⁶O and ₈¹⁸O

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Isotopes

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 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 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

¹⁰X has a percent abundance of 19.8% and ¹¹X has a percent abundance of 80.2%. What is the average atomic mass of the hypothetical element X?

• 10.41 amu

• 10.50 amu

• 10.80 amu

• 11.52 amu

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average atomic mass

Element Q is an unknown element. ²⁰Q has abundance of 90.51%, ²¹Q has abundance of 0.21%, and ²²Q 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

Identify the element with the mass spectra shown below:

• Beryllium

• Lithium

• Boron

• Helium

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average atomic mass

What element is represented by the mass spectrum shown below?

• Tungsten

• Osmium

• Tantalum

• Rhenium

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average atomic mass

Estimate the mass and identify of the element with the given mass spectra shown below.

• Zinc - 65.4 amu

• Copper - 63.5 amu

• Nickel - 58.9 amu

• Gallium - 69.1 amu

Which of the following represents isotopes of the element ₂₂⁴⁹Q only?

• ₂₂³⁸Q and ₂₂⁵⁰Q

• ₉²²Q and ₁₉²⁹Q

• ₉¹⁹Q and ₂₂⁵⁹Ne

• ₂₂⁴⁹Q and ₁₉⁴⁹Q