Multiple Choice
How is the average atomic mass of an element calculated?
2. Atoms & Elements
Atomic Mass
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How is the atomic mass of bromine calculated given its isotopes, Br-79 with 51% abundance and Br-81 with 49% abundance?
A
By using the isotope with the highest abundance as the atomic mass.
B
By adding the mass numbers of the isotopes and dividing by two.
C
By taking the weighted average of the isotopic masses based on their abundances.
D
By averaging the mass numbers of the isotopes.
Verified step by step guidance1
Understand that the atomic mass of an element is calculated using the weighted average of its isotopic masses based on their relative abundances.
Identify the isotopes of bromine: Br-79 and Br-81, with their respective abundances of 51% and 49%.
Convert the percentage abundances into decimal form for calculation: 51% becomes 0.51 and 49% becomes 0.49.
Use the formula for weighted average: \( \text{Atomic Mass} = (\text{Mass of Br-79} \times \text{Abundance of Br-79}) + (\text{Mass of Br-81} \times \text{Abundance of Br-81}) \).
Substitute the values into the formula: \( \text{Atomic Mass} = (79 \times 0.51) + (81 \times 0.49) \) and perform the calculations to find the atomic mass of bromine.
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