Suppose a new element is discovered and it has two stable isotopes. One isotope has a mass of 73.942 u and an abundance of 38.92%. The average atomic mass of the element is 73.970 u. What is the mass of the second isotope?

73.988 amu

Explanation:

Given dа ta:

Abundance of 1st isotope = 38.92%

Abundance of 2nd isotope = 61.08%

Atomic mass of 1st isotope = 73.942 amu

Atomic mass of 2nd isotope = ?

Average atomic mass = 73.970 amu

Solution:

Average atomic mass = (abundance of 1st isotope * its atomic mass) + (abundance of 2nd isotope * its atomic mass) / 100

73.970 = (38.92*73.942) + (61.08*atomic mass) / 100

73.970 * 100 = 2877.823 + (61.08*atomic mass)

7397 = 2877.823 + (61.08*atomic mass)

7397 - 2877.823 = (61.08*atomic mass)

4519.18 = 61.08*atomic mass

4519.18 / 61.08 = atomic mass

73.988 amu = atomic mass