Question

An element comprises three isotopes with masses of 28, 29, & 30 atomic mass units (amu). The relative abundances of these isotopes are 92.23%, 4.67%, & 3.10% respectively. What is the average atomic mass of this element?

A. 29.3 amu
B. 28.0 amu
C. 28.1 amu
D. 29.7 amu

Answer 1

The average atomic mass of an element with isotopes weighing 28, 29, and 30 amu, and respective relative abundances of 92.23%, 4.67%, and 3.10%, calculates to 28.1087 amu. Therefore, the nearest correct answer is 28.1 amu.

Step-by-step explanation:

To calculate the average atomic mass of an element based on the isotopic masses and their natural abundances, you multiply each isotope's mass by its relative abundance (expressed as a decimal), then sum these products. For the element with isotopes of masses 28 amu, 29 amu, and 30 amu, the calculation would be as follows:

• (28 amu × 0.9223) + (29 amu × 0.0467) + (30 amu × 0.0310)
• (25.8244) + (1.3543) + (0.930)
• 28.1087 amu

After completing the calculation, we see that the average atomic mass is 28.1087 amu. Therefore, based on the options provided, the closest answer to the average atomic mass of this element is C. 28.1 amu.