Question

A certain element occurs naturally in three isotopic forms:

- 85.3% X-40, with a relative atomic mass of 40.3 amu
- 10.4% X-42, with a relative atomic mass of 41.9 amu
- 4.30% X-44, with a relative atomic mass of 44.4 amu
Calculate the average atomic mass of element X and identify which element it is likely to be.

Answer 1

To calculate the average atomic mass of an element with three naturally occurring isotopes, multiply the mass of each isotope by its abundance and sum the results. The average atomic mass of element X is approximately 40.777 amu.

Step-by-step explanation:

To calculate the average atomic mass of an element with three naturally occurring isotopes, we multiply the mass of each isotope by its abundance and sum the results. In this case:

• The first isotope, X-40, has a relative atomic mass of 40.3 amu and an abundance of 85.3% (0.853).
• The second isotope, X-42, has a relative atomic mass of 41.9 amu and an abundance of 10.4% (0.104).
• The third isotope, X-44, has a relative atomic mass of 44.4 amu and an abundance of 4.30% (0.0430).

Now, we multiply each mass by its abundance:

• (40.3 amu * 0.853) = 34.5199 amu
• (41.9 amu * 0.104) = 4.3436 amu
• (44.4 amu * 0.0430) = 1.9152 amu

Finally, we add all of the weighted masses together:

• 34.5199 amu + 4.3436 amu + 1.9152 amu = 40.7787 amu

Therefore, the average atomic mass of element X is approximately 40.777 amu.