In 1961, the Commission recommended Ar (Cu) = 63.54 based on the recent chemical determinations. In 1967, the Commission recommended Ar (Cu) = 63.546 (1) based on. ››More information on molar mass and molecular weight. In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all.

1. Atomic Mass of Copper Atomic mass of Copper is 63.546 u. Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance. The unit of measure for mass is the atomic mass unit (amu).
2. Aluminum is a chemical element with symbol Al and atomic number 13. Classified as a post-transition metal, Aluminum is a solid at room temperature.

How would you calculate the average atomic mass of copper if 69.2% of copper has a mass of 62.93 amu and 30.8% has a mass of 64.93 amu?

1 Answer

Explanation:

The average atomic mass of an element is calculated by taking the weighted average of the atomic masses of its naturally-occurring isotopes.

Simply put, each isotope will contribute to the average atomic mass of the element proportionally to its percent abundance.

#color(blue)('avg. atomic mass' = sum_i ('isotope'_i xx 'abundance'_i)#

Atomic Mass Of Copper-65

As far as the actual calculations go, you will use decimal abundances, which are simply percent abundances divided by #100#.

Atomic Mass Of Copper In Kg

So, you know that the atomic masses of these two copper isotopes are #'62.93 u'# and #'64.93 u'#, respectively. Their decimal abundances will be #0.692# and #0.308#, respectively.

The average atomic mass of copper will thus be

#'avg. atomic mass' = overbrace('62.93 u' xx 0.692)^(color(red)(1^'st' 'isotope')) + overbrace('64.93 u' xx 0.308)^(color(red)(2^'nd' 'isotope'))#

#'avg. atomic mass ' = color(green)(' 63.546 u')#

Atomic Mass Of Copper 63

I'll leave the answer is rounded to four sig figs, despite the fact that the values you have for the percent abundances justify only three sig figs.

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