Answer:
17.20 amu
Step-by-step explanation:
Depending on the number of isotopes, the average atomic mass of an isotopic element can be calculated using the expression:
Average atomic mass = (mass of isotope1 × decimal abundance of isotope1) + (mass of isotope2 × decimal abundance of isotope2)...........
In this case, Tony is trying to find the average atomic mass of an unknown element.
- The first isotope of the element has mass= 15.97 amu, and percent abundance= 34.7%.
- The other isotope has mass= 17.85 amu, and percent abundance= (100-34.7) = 65.3%.
Decimal abundance of isotope1 = 34.7/100 = 0.347
Decimal abundance of isotope2 = 65.3/100 = 0.653
Therefore, the average atomic mass =
(15.97 × 0.347) + (17.85 × 0.653)
= 5.54159 + 11.65605
= 17.19764
= 17.20 amu