Answer:
6.018 amu
Explanation:
Let 6–Li be isotope A.
Let 7–Li be isotope B.
Let the abundance of 6–Li be A%
Let the abundance of 7–Li be B%
The following data were obtained from the question:
Atomic mass of isotope A (6–Li) =.?
Atomic mass of isotope B (7–Li ) = 7.015 amu.
Abundance of 7–Li (B%) = 92.58%
Abundance of 6–Li (A%) = 100 – B% = 100 – 92.58 = 7.42%
Atomic mass of Lithium = 6.941amu
The atomic mass of isotope A (6–Li) can be obtained as follow:
Atomic mass = [(Mass of A x A%)/100] + [(Mass of B x B%)/100]
6.941 = [(mass of A x 7.42)/100] + [(7.015x92.58)/100]
6.941 = [(mass of A x 7.42)/100] + 6.494487
(mass of A x 7.42)/100 = 6.941 – 6.494487
(mass of A x 7.42)/100 = 0.446513
Mass of A x 7.42 = 100 x 0.446513
Mass of A x 7.42 = 44.6513
Divide both side by 7.42
Mass of A = 44.6513 / 7.42
Mass of A = 6.018 amu
Therefore, the mass of 6–Li is 6.018 amu
