A sample of chlorine has two naturally occurring isotopes. The isotope Cl-35 (mass 35.0 amu) makes up 75.8% of the sample, and the isotope Cl-37 (mass = 37.0 amu) makes up 24.3% of the sample. What is the average atomic mass for chlorine?
A)36.0 amu
B)35 amu
C)36.6 amu
D)35.5 amu
E)35.521 amu

Question

Quizplus · Accepted Answer

To find the average atomic mass, we use the formula:

average atomic mass = (% abundance of isotope 1 × mass of isotope 1) + (% abundance of isotope 2 × mass of isotope 2)

Plugging in the values given, we get:

average atomic mass = (0.758 × 35.0 amu) + (0.243 × 37.0 amu)

= 26.53 amu + 8.97 amu

= 35.50 amu

Therefore, the average atomic mass for chlorine is 35.5 amu (option D).

A Sample of Chlorine Has Two Naturally Occurring Isotopes