Multiple Choice
Isotopes of an element differ from one another in the number of which subatomic particles they contain?
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2. Atoms & Elements
Isotopes
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A sample of chlorine contains two naturally occurring isotopes: chlorine-35 (mass = 34.969 u, abundance = 75.78%) and chlorine-37 (mass = 36.966 u, abundance = 24.22%). What is the average atomic mass of chlorine?
A
34.97 u
B
35.00 u
C
35.45 u
D
36.00 u
Verified step by step guidance1
Identify the isotopes of chlorine and their respective masses and abundances: chlorine-35 with mass 34.969 u and abundance 75.78%, and chlorine-37 with mass 36.966 u and abundance 24.22%.
Convert the percentage abundances into decimal form by dividing each by 100: 75.78% becomes 0.7578 and 24.22% becomes 0.2422.
Calculate the weighted contribution of each isotope to the average atomic mass by multiplying the mass of each isotope by its decimal abundance: for chlorine-35, multiply 34.969 u by 0.7578; for chlorine-37, multiply 36.966 u by 0.2422.
Add the weighted contributions of both isotopes together to find the average atomic mass of chlorine: average atomic mass = (mass of isotope 1 × abundance 1) + (mass of isotope 2 × abundance 2).
Express the final result with appropriate units (atomic mass units, u) and compare it to the given options to confirm the correct average atomic mass.
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