Question

There are 2 stable isotopes of copper: copper-63, which is 69.15% of naturally occuring stable copper, and copper-65, which is 30.85% of naturally occuring stable copper. The atomic mass of copper-63 is 62.93 amu, and the atomic mass of copper-65 is 64.93 amu. How should the average atomic weight of copper be calculated?

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Neon-20 has an atomic mass of 19.992 amu and a relative abundance of 90.48%; neon-21 has an atomic mass of 20.994 amu and a relative abundance of 0.27%; and neon-22 has an atomic mass of 21.991 amu and a relative abundance of 9.25%. How should the average atomic weight of neon be calculated?



Stable sulfur consists of sulfur-32, sulfur-33, sulfur-34, and sulfur-35, which have relative abundances of 95.002%, 0.76%, 4.22% and 0.014%, respectively, and respective masses of 31.972 amu, 32.971 amu, 33.967 amu, and 34.967 amu. How should the atomic mass of sulfur be calculated?



Use the following isotope information to calculate the atomic mass of iron and show your work.

Mass Numbers: 54, 56, 57, 58

Abundance: 5.845%, 91.754%, 2.119%, 0.282%

Atomic Masses: 53.940 amu, 55.934 amu, 56.935 amu, 57.933 amu



Natural abundances vary based on the planet and its formation history. For example, Mars and Earth have different oxygen isotope ratios. It has been suggested that the moon was formed when a planet-sized object struck a glancing blow on Earth. Although the cores remained largely intact, the remnants of these two bodies eventually reformed into Earth and moon. Explain how you could use isotopic analysis to test this hypothesis.

Answer 1

The average atomic weight of an element like copper is calculated by taking the weighted average based on the relative abundances and masses of its isotopes. This involves multiplying each isotope's mass with its abundance (converted to a decimal), and then summing these values to find the overall average atomic mass.

Step-by-step explanation:

The average atomic weight of an element is calculated by using the weighted average of the masses of its isotopes based on their natural abundance. For copper, for instance, we will calculate the average atomic mass by multiplying the mass of each isotope by its relative abundance and then summing the products. The formula to calculate this is as follows:

Average atomic mass of Cu = (mass of Cu-63 × relative abundance of Cu-63) + (mass of Cu-65 × relative abundance of Cu-65)

This is done by converting the percent abundances to decimal form (by dividing them by 100) and then using the mentioned formula:

Average atomic mass of Cu = (62.93 amu × 0.6915) + (64.93 amu × 0.3085)

• Calculate the product of each isotope's mass and its converted abundance.
• Sum the results to find the average atomic mass

Similarly, the average atomic mass of other elements, such as neon or iron, is determined using the same method, with their respective isotopic masses and abundances.