Question

A sample of Element X is found to contain 72.15% of isotope type 1 (84.91 amu) and 27.85% of isotope type 2 (86.91 amu). Calculate the average atomic mass.

A) 85.55 amu
B) 85.12 amu
C) 85.20 amu
D) 85.75 amu

Answer 1

The average atomic mass, multiply the mass of each isotope by its relative abundance in decimal form, then add the products together. The result for Element X is an average atomic mass of 85.51 amu, which rounds to 85.55 amu, and the correct answer is A) 85.55 amu.

Step-by-step explanation:

The question involves calculating the average atomic mass of an element based on the given abundances and masses of its isotopes. To find the average atomic mass, we multiply the mass of each isotope by its relative abundance (converted from a percentage to a decimal), and then sum these values. The calculation for Element X with 72.15% of isotope 1 (84.91 amu) and 27.85% of isotope 2 (86.91 amu) will be:

• (0.7215 × 84.91 amu) = 61.305065 amu
• (0.2785 × 86.91 amu) = 24.205635 amu

Adding both products together gives the average atomic mass of Element X:

61.305065 amu + 24.205635 amu = 85.5107 amu

The closest answer to our calculation is 85.51 amu, which would be rounded to 85.55 amu as per usual rounding rules, so the correct answer is Option A).