Table of contents

1. Intro to General Chemistry3h 48m
2. Atoms & Elements4h 16m
3. Chemical Reactions4h 10m
4. BONUS: Lab Techniques and Procedures1h 38m
5. BONUS: Mathematical Operations and Functions48m
6. Chemical Quantities & Aqueous Reactions3h 53m
7. Gases3h 49m
8. Thermochemistry2h 37m
9. Quantum Mechanics2h 58m
10. Periodic Properties of the Elements3h 9m
11. Bonding & Molecular Structure3h 29m
12. Molecular Shapes & Valence Bond Theory1h 57m
13. Liquids, Solids & Intermolecular Forces2h 23m
14. Solutions3h 1m
15. Chemical Kinetics2h 53m
16. Chemical Equilibrium2h 29m
17. Acid and Base Equilibrium5h 1m
18. Aqueous Equilibrium4h 47m
19. Chemical Thermodynamics1h 50m
20. Electrochemistry2h 42m
21. Nuclear Chemistry2h 36m
22. Organic Chemistry5h 7m
23. Chemistry of the Nonmetals2h 39m
24. Transition Metals and Coordination Compounds3h 16m

2. Atoms & Elements

Atomic Mass

General Chemistry

2. Atoms & Elements

Atomic Mass

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Multiple Choice

Element A has two isotopes. The first isotope is present 24.01% of the time and has a mass of 131.96 amu. The second isotope has a mass of 113.66 amu. Calculate the atomic mass of element A.

118.74 amu

120.50 amu

117.35 amu

125.30 amu

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Verified step by step guidance

Understand that the atomic mass of an element is the weighted average of the masses of its isotopes, based on their natural abundance.

Convert the percentage of the first isotope's abundance into a decimal by dividing by 100. For the first isotope, 24.01% becomes 0.2401.

Calculate the contribution of the first isotope to the atomic mass by multiplying its mass (131.96 amu) by its decimal abundance (0.2401). Use the formula:

mass \times abundance

Assume the second isotope's abundance is the remainder of 100% after accounting for the first isotope. Calculate this by subtracting the first isotope's abundance from 1:

1 - 0.2401

Calculate the contribution of the second isotope to the atomic mass by multiplying its mass (113.66 amu) by its decimal abundance. Add the contributions from both isotopes to find the atomic mass of element A.