Q: Which formula is used to calculate the atomic mass of an element with multiple isotopes?

$\text{Atomic Mass} = \sum (\text{Isotope Mass} \times \text{Fractional Abundance})$

Q: Which of the following choices has the greatest atomic mass?

Element D (3.14 \times 10^{24} Da)

Question 1

Which of the following statements best describes atomic mass as presented in the study materials?

Accepted Answer

Atomic mass is the average mass of all isotopes of an element, weighted by their percent abundance.

Question 2

Given the following isotopic data for element X: $^{30}X$ (mass = 30.0 amu, abundance = 70%) and $^{32}X$ (mass = 32.0 amu, abundance = 30%), what is the atomic mass of element X?

Accepted Answer

$30.6$ amu

Question 3

Which of the following elements from the first column of the periodic table has the greatest atomic mass?

Accepted Answer

Cs

Question 4

If an element has two isotopes: $^{10}A$ (mass = 10.012 amu, abundance = 19.91%) and $^{11}A$ (mass = 11.009 amu, abundance = 80.09%), calculate the atomic mass of element A.

Accepted Answer

$10.81$ amu

Question 5

Which formula is used to calculate the atomic mass of an element with multiple isotopes?

Accepted Answer

$	ext{Atomic Mass} = \sum (	ext{Isotope Mass} 	imes 	ext{Fractional Abundance})$

Question 6

A sample of magnesium contains three isotopes: $^{24}Mg$ (mass = 23.9850 amu, abundance = 78.70%), $^{25}Mg$ (mass = 24.9858 amu, abundance = 10.13%), and $^{26}Mg$ (mass = 25.9826 amu, abundance = 11.17%). What is the atomic mass of magnesium?

Accepted Answer

$24.3050$ amu

Question 7

Silver has an atomic mass of $107.868$ amu. The Ag-109 isotope (mass = $108.905$ amu) is $48.16\%$ abundant. What is the mass of the other isotope (Ag-107)?

Accepted Answer

$106.905$ amu

Question 8

Which of the following choices has the greatest atomic mass?

Accepted Answer

Element D (3.14 	imes 10^{24} Da)

Question 9

Why is the atomic mass of most elements not a whole number?

Accepted Answer

Because it is the weighted average of the masses of all naturally occurring isotopes.

Question 10

If you are given percent abundances, what must you do before using them in the atomic mass formula?

Accepted Answer

Divide them by 100 to convert to fractional abundances.

Question 11

A scientist discovers a new element with two isotopes: $^{200}X$ (mass = 200 amu, abundance = 60%) and $^{202}X$ (mass = 202 amu, abundance = 40%). What is the atomic mass of the element?

Accepted Answer

$200.8$ amu

Question 12

Which of the following best explains why isotopic abundance is important in calculating atomic mass?

Accepted Answer

It determines how much each isotope contributes to the average atomic mass.

Atomic Mass: Concepts, Calculations, and Practice

Study Guide - Practice Questions

Study Guide - Flashcards