Which numerical setup can be used to calculate the atomic mass of the element copper, given that copper has two naturally occurring isotopes: Cu-63 (abundance 69.17%, mass 62.93 u) and Cu-65 (abundance 30.83%, mass 64.93 u)?

• A. (69.17 × 62.93) + (30.83 × 64.93)
• B. (0.3083 × 62.93) + (0.6917 × 64.93)
• C. (0.6917 × 62.93) + (0.3083 × 64.93)
• D. (62.93 + 64.93) / 2

Answer: (C)

Verified step by step guidance

1. Understand that the atomic mass of an element with multiple isotopes is the weighted average of the masses of its isotopes, where the weights are their relative abundances expressed as decimals.
2. Convert the given percentage abundances of each isotope into decimal form by dividing by 100. For example, 69.17% becomes 0.6917 and 30.83% becomes 0.3083.
3. Set up the weighted average formula for atomic mass as: \(\text{Atomic Mass} = (\text{fractional abundance of isotope 1} \times \text{mass of isotope 1}) + (\text{fractional abundance of isotope 2} \times \text{mass of isotope 2})\).
4. Substitute the decimal abundances and isotope masses into the formula: \(\text{Atomic Mass} = (0.6917 \times 62.93) + (0.3083 \times 64.93)\).
5. This setup correctly accounts for the contribution of each isotope to the overall atomic mass based on their natural abundances.