Considering the definition of atomic mass, isotopes and atomic mass of an element, the isotope with masses of 62.939598 amu and 64.927793 amu have percent abundances of 69.80% and 30.20% respectively.
The atomic mass (A) is obtained by adding the number of protons and neutrons in a given nucleus of a chemical element.
The same chemical element can have the same atomic numbers, but the number of neutrons is different. These atoms are called isotopes of the element.
The atomic mass of an element is the weighted average mass of its natural isotopes, taking into account the relative abundance of each of them.
In this case, you know:
The percent abundance can be calculated as:
62.939598 amu× (x%÷100%) + 64.927793 amu× [(100-x)%÷100%]= 63.54 amu
Solving:
62.939598 amu× x+ 64.927793 amu× (1-x)= 63.54 amu
62.939598 amu× x+ 64.927793 amu× 1- 64.927793 amu× x= 63.54 amu
62.939598 amu× x- 64.927793 amu× x= 63.54 amu - 64.927793 amu× 1
-1.988195 amu× x= -1.387793 amu
x= (-1.387793 amu)÷ (-1.988195 amu)
x= 0.6980= 69.80%
Then, (100-x)%= (100 -69.80)%= 30.2%
Finally, the isotope with mass of 62.939598 amu has a percent abundance of 69.80% and the isotope with mass of 64.927793 amu has a percent abundance of 30.20%.
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