A sample of chlorine has two naturally occurring isotopes.The isotope Cl-35 makes up 75.8% of the sample,and the isotope Cl-37 makes up 24.3% of the sample.Which of the following statements is true?
A)The atomic mass of chlorine will be less than 35.
B)The atomic mass of chlorine will be more than 37.
C)You cannot tell what the atomic mass will be.
D)The atomic mass will be between 35 and 37.
E)The atomic mass will be 24.3.

Question

Quizplus · Accepted Answer

The atomic mass of chlorine will be a weighted average of the atomic masses of the isotopes, weighted according to their abundances. The atomic mass of Cl-35 is approximately 35, while the atomic mass of Cl-37 is approximately 37. Therefore, the atomic mass of chlorine will be between 35 and 37, closer to 35 because Cl-35 is more abundant in the sample. Choice A and B are incorrect because the atomic mass will definitely fall within the range defined by the isotopes. Choice C is also incorrect because the atomic mass can be calculated based on the abundances of the isotopes. Choice E is incorrect because it refers to the abundance of Cl-37, not the atomic mass.

A Sample of Chlorine Has Two Naturally Occurring Isotopes