Naturally occurring iodine has an atomic mass of 126.9045...

Naturally occurring iodine has an atomic mass of 126.9045 amu. A 12.3849 g sample of iodine is accidentally contaminated with an additional 1.00070 gof $^{129} 1,$ a synthetic radioisotope of iodine used in the treatment of certain diseases of the thyroid gland. The mass of 129 I is 128.9050 amu. Find the apparent "atomic mass" of the contaminated iodine.

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Key Concepts

Atomic Mass

Atomic mass is the weighted average mass of all atoms of an element, reflecting the relative proportions of its different isotopes. It is measured in atomic mass units (amu) and represents the average mass of an atom of the element, rather than the mass of any single isotope.

Isotopes

Isotopes are forms of an element that have the same number of protons but different numbers of neutrons in their nuclei. Although they share chemical properties, the differences in their nuclear composition result in different atomic masses, affecting calculations that involve the average mass of the element.

Weighted Average Calculation

Weighted average calculation involves determining an overall value by multiplying each isotope's mass by its relative abundance, summing these products, and dividing by the total abundance. This approach is used to compute the apparent atomic mass of a sample that contains a mixture of isotopes.

Isotopic Composition and Contamination

Isotopic composition refers to the distribution of different isotopes within a sample of an element. When a sample is contaminated by an isotope with a different mass, the overall weighted average atomic mass is altered. Understanding this concept is crucial for accurately determining the apparent atomic mass in situations where the natural isotopic abundance is modified.

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