Ch.2 - Atoms & ElementsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: Three isotopes of A (Isotope 1: 85.91 amu, 35.12%, Isotope 2: 86.91 amu, abundance 7%, Isotope 3: 87.91 amu) would have the atomic mass of what?

Problem

Three isotopes of A (Isotope 1: 85.91 amu, 35.12%, Isotope 2: 86.91 amu, abundance 7%, Isotope 3: 87.91 amu) would have the atomic mass of what?

Solution

We’re being asked to determine the average atomic mass given the mass of 3 isotopes.


We can use the following equation:


Atomic Mass=[mass×f.a.]isotope 1+[mass×f.a.]isotope 2+[mass×f.a.]isotope 3


where:

atomic mass = average atomic mass of the element 

f.a. = fractional abundance of the isotope

To get f.a., we simply need to divide the given percent abundance by 100.


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