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Bromine has two naturally-occurring isotopes. 79Br has a mass of 78.9 amu and accounts for 50.3% of bromine atoms. If the atomic mass of bromine is 79.9 amu, what is the mass of an atom of the second bromine isotope?
A) 77.9 amu.
B) 80.0 amu.
C) 80.1 amu.
D) 80.9 amu.
E) 88.9 amu.

Respuesta :

tutorAnne

The mass of an atom of the second bromine isotope is 80.9amu

Calculation of Mass of an atomic isotope

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

Now given that

  • Atomic mass of bromine = 79.9 amu
  • Percent abundance of 1st isotope = 50.3%
  • Atomic mass of 1st isotope = 78.9 amu
  • Percent abundance of 2nd isotope = 100-50.3%=49.7%
  • Atomic mass of 2nd isotope =?

Plugging in values, we have that

79.9= (50.3×78.9)+(49.7× ?) /100

79.9x 100= (50.3×78.9)+(49.7× ?) /100

7990= 3968.7+(49.7x)

7990- 3968.7=49.7x

4021.3= 49.7x

x=4021.3/49.7

x=80.9amu

Therefore, the  mass of an atom of the second bromine isotope is 80.9amu.

See related question on finding mass of an isotope here: https://brainly.com/question/19533439

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