Problem: Only two isotopes of copper occur naturally, 63 Cu (atomic mass = 62.9296  amu; abundance 69.17 %) and 65 Cu (atomic mass = 64.9278  amu; abundance 30.83 %).Calculate the atomic weight (average atomic mass) of copper.

FREE Expert Solution

We are asked to determine the atomic weight (average molecular mass) of a Copper (Cu) given 63 Cu (atomic mass = 62.9296  amu; abundance 69.17 %) and 65 Cu (atomic mass = 64.9278  amu; abundance 30.83 %).


We will solve for atom’s average mass using their abundance. 

The formula for average mass is:

Average molecular mass = (Mass isotope × Fractional Abundance)

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Problem Details

Only two isotopes of copper occur naturally, 63 Cu (atomic mass = 62.9296  amu; abundance 69.17 %) and 65 Cu (atomic mass = 64.9278  amu; abundance 30.83 %).

Calculate the atomic weight (average atomic mass) of copper.

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