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If two isotopes of an element тАШXтАЩ are X-35 and X-37, the average atomic mass of chlorine (if X-35 = 25% and X-37 = 75%) will be:
35.5 u
36.0 u
34.5 u
36.5 u
36.5 u
The average atomic mass of an element is calculated by taking the weighted average of the masses of its naturally occurring isotopes. Using the provided values, the calculation yields 36.5 u.
The average atomic mass of an element is calculated by taking the weighted average of the masses of its naturally occurring isotopes. Using the provided values, the calculation yields 36.5 u.
Think of this like calculating your final grade where the midterm counts for 25% and the final exam counts for 75%; you weigh each score by how much it contributes to the total.
W-A-M: Weighted Average Mass.
Average┬аMass=тИС(miтАЛ├ЧaiтАЛ) тАФ where miтАЛ is the mass and aiтАЛ is the fractional abundance of the isotope.
The average atomic mass is computed using the formula Average┬аAtomic┬аMass=тИС(FractionalAbundance├ЧIsotopic┬аMass). Here, the abundance of X-35 is 25% (0.25) and X-37 is 75% (0.75). Thus, (35├Ч0.25)+(37├Ч0.75)=8.75+27.75=36.5u.
Isotopes have the same atomic number but different mass numbers due to a different number of neutrons.
The weighted average reflects the natural percentage distribution of isotopes in a sample.
Standard atomic mass in the Periodic Table is derived from these precise natural abundance values.
Provides a single representative value for chemical calculations.
Accounts for the varying stability and occurrence of different isotopes.
The 'average' mass does not correspond to the actual mass of any single atom of the element.
Mass spectrometry analysis.
Determining stoichiometric ratios in chemical reactions.
The natural abundance of Chlorine isotopes is actually Chlorine-35 (~75%) and Chlorine-37 (~25%), resulting in the standard atomic mass of 35.5 u.
The official answer provided in the prompt (36.5 u) is mathematically correct based on the specific hypothetical percentages given in the question (25% and 75%), despite being the inverse of real-world Chlorine abundance.
D is correct тАФ The weighted average of the isotopes based on the provided percentages (35├Ч0.25+37├Ч0.75) results in 36.5 u.
Always verify if the question uses standard natural abundances or custom hypothetical values provided in the prompt, as standard values (like Cl = 35.5) may not apply if percentages are altered.
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