Question

Element X with mass number 121 has percent abundance of 57.21% and has a mass of 120.9038 amu, while the other isotope with a mass number of 123 has percent abundance of 42.79% and has a mass of 122.9042 amu. What is the weighted average atomic mass that should be reported for element X?

Answer 1

The weighted average atomic mass of element X considering its two isotopes with given percent abundances and masses is 121.8078 amu.

Step-by-step explanation:

To calculate the weighted average atomic mass for element X, we will use the percent abundances and masses of its isotopes. We first convert the percentages into fractions by dividing by 100. The calculation is as follows:

• (0.5721 × 120.9038 amu) for isotope with mass number 121
• (0.4279 × 122.9042 amu) for isotope with mass number 123

We then add the products to obtain the weighted average atomic mass:

Weighted Average = (0.5721 × 120.9038) + (0.4279 × 122.9042)

Weighted Average = 69.1766 + 52.6312 = 121.8078 amu

Therefore, the weighted average atomic mass that should be reported for element X is 121.8078 amu.