An element has three stable isotopes with masses of 27.977 amu,28.976 amu,and 29.973 amu.The heavier two isotopes have an abundance of 4.68% and 3.09%,respectively.What is the mass of the element?
A) 27.684 amu
B) 29.251 amu
C) 28.085 amu
D) 30.107 amu
E) 28.991 amu

Question

Quizplus · Accepted Answer

To calculate the mass of the element, we need to take the weighted average of the masses of its isotopes, using their relative abundances as weights.

Mass of element = (0.0468)(28.976 amu) + (0.0309)(29.973 amu) + (1 - 0.0468 - 0.0309)(27.977 amu)
Mass of element = 1.357208 + 0.928397 + 0.691395
Mass of element = 2.976 amu

Therefore, the mass of the element is 28.085 amu, which is option C.

An Element Has Three Stable Isotopes with Masses of 27