iodin is 80% ^127 I, 17% ^126 I, and 3% ^128 I. calculate the average atomic mass of iodine.

1 answer

To calculate the average atomic mass of iodine, we can use the formula:

\[ \text{Average Atomic Mass} = \sum (\text{fraction} \times \text{isotope mass}) \]

where the fractions are the decimal representations of the percentages of each isotope.

Let's break it down for each isotope:

  1. Isotope \(^{127}\text{I}\):

    • Percentage: 80%
    • Fraction: \(0.80\)
    • Atomic mass: \(127 , \text{amu}\)
    • Contribution: \(0.80 \times 127 = 101.6 , \text{amu}\)
  2. Isotope \(^{126}\text{I}\):

    • Percentage: 17%
    • Fraction: \(0.17\)
    • Atomic mass: \(126 , \text{amu}\)
    • Contribution: \(0.17 \times 126 = 21.42 , \text{amu}\)
  3. Isotope \(^{128}\text{I}\):

    • Percentage: 3%
    • Fraction: \(0.03\)
    • Atomic mass: \(128 , \text{amu}\)
    • Contribution: \(0.03 \times 128 = 3.84 , \text{amu}\)

Now, we can add together all of the contributions:

\[ \text{Average Atomic Mass} = 101.6 + 21.42 + 3.84 = 126.86 , \text{amu} \]

Thus, the average atomic mass of iodine is approximately \( \mathbf{126.86} , \text{amu} \).