Tony is trying to find the average atomic mass of an unknown element. He has a sample where 34.7% of the atoms have a mass of 15.97 amu, while the rest have a mass of 17.85 amu. What is the average atomic mass of Tony's sample?

17.20 amu

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

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