Q26E - Chemistry (OpenStax)

Question

The ¹⁸O: ¹⁶O abundance ratio in some meteorites is greater than that used to calculate the average atomic mass of oxygen on earth. Is the average mass of an oxygen atom in these meteorites greater than, less than, or equal to that of a terrestrial oxygen atom?

Step-by-Step Solution

Answer

The average atomic mass of an oxygen atom will be greater than the terrestrial oxygen atom.

Step 1 – Determine the definition of average atomic mass

The mass of an element of atomic masses is a weighted, average mass of all the isotopes present in a naturally occurring sample of that element. This is equal to the sum of each individual isotope’s mass multiplied by its fractional abundance.

Step 2 – Determine the Formula of Average mass

Average mass = \(\sum\limits_i {{{(fractional\,\,abundance \times isotopic\,mass)}_i}} \)

Step 3 – Determine how the average atomic mass of an oxygen atom will be greater than the terrestrial oxygen atom

It is because the average atomic mass of an element is directly proportional to the fractional abundance of the isotopes. So, if abundance increases then the average atomic mass also increases.