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What is the average atomic mass of an element if, out of 100 atoms, 5 have a mass of 176 amu, 19 have a mass of 177 amu, 27 have a mass of 178 amu, 14 have a mass of 179 amu, and 35 have a mass of 180 amu?

Md Ariful Islam

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Md Ariful Islam

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The $"Average Atomic Mass"$ of an element is defined as "the weighted average mass of all naturally-occurring (occasionally radioactive) of the element." (and hence the name "average") [1]

Dividing the sum of the product of the $color(purple)("relative atomic mass of each of the isotope")$ and $color(grey)("the occasion of their presence in the sample")$ by $"the sum of atoms in the sample"$ gives the weighted average of the relative .

$"Average Atomic Weight" $
$= (color(grey)(5) xx color(purple)(176) + color(grey)(19) xx color(purple)(177) + color(grey)(27) xx color(purple)(178) + color(grey)(14) xx color(purple)(179) + color(grey)(35) xx color(purple)(180)) / (color(black)(100))$
$= 178.55 color(white)(l) "amu"$

Reference
[1] Vitz, Ed, et al. “4.13: Average Atomic Weights.” Chemistry LibreTexts, Libretexts, 5 Sept. 2017,
(Moore_et_al.)/04The_Structure_of_Atoms/4.13:_Average_Atomic_Weights.

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2. The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for a mass of 62.93 amu and 30.8% for a mass of 64.93 amu. How do you calculate the average atomic mass of copper?

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1 Answers 1 views
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1 Answers 1 views

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