Calculate the atomic mass of carbon if the two common isotopes of carbon have masses of
12.000 amu (98.89 % abundance) and 13.003 amu (1.11 % abundance)

Average atomic mass of carbon = 12.01 amu.

Explanation:

Given data:

Abundance of C¹² = 98.89%

Abundance of C¹³ = 1.11%

Atomic mass of C¹² = 12.000 amu

Atomic mass of C¹³ = 13.003 amu

Average atomic mass = ?

Solution:

Average atomic mass of carbon = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass of carbon = (12.000×98.89)+(13.003×1.11) /100

Average atomic mass of carbon=  1186.68 + 14.43333 / 100

Average atomic mass of carbon = 1201.11333 / 100

Average atomic mass of carbon = 12.01 amu.

Considering the definition of isotopes and atomic mass, the atomic mass of Carbon is 12.011 amu.

First of all, the isotopes of an element are those in which its atomic numbers (that is, the number of protons) are the same, but the number of neutrons is different. Remember that protons and neutrons are in the nucleus of the element.

The same chemical element can be made up of different atoms, that is, different isotopes.

So the atomic mass of an element is the weighted average mass of its natural isotopes. Therefore, the atomic mass of an element is not a whole number.

The relative abundance of an isotope is the percentage of atoms with a specific atomic mass found in a naturally occurring sample of an element.

The atomic masses of chemical elements are usually calculated as the weighted average of the masses of the different isotopes of each element, taking into account the relative abundance of each of them.

In this case, taking into account that the two common isotopes of carbon have masses of  12.000 amu (98.89 % abundance) and 13.003 amu (1.11 % abundance), the atomic mass of the element is calculated as:

12 amu×0.9889 + 13.003 amu×0.0111= 12.011 amu

In summary, the atomic mass of Carbon is 12.011 amu.

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