Zinc has five naturally occurring isotopes, Zn-64, Zn-66, Zn-67, Zn-68 and Zn-70. Calculate the atomic mass of zinc given the following abundances and atomic masses for the isotopes: Zn-64 63.9291 amu 48.61%
Zn-66 65.9260 amu 27.9%
Zn-67 66.9271 amu 4.1%
Zn-68 67.9248 amu 18.75%
Zn-70 69.9253 amu 0.62%
A)65.34 amu
B)65.38 amu
C)65.65 amu
D)65.19 amu
E)65.85 amu

Question

Quizplus · Accepted Answer

To calculate the atomic mass, we need to multiply the abundance of each isotope by its atomic mass, then add up the products.

Atomic mass of Zn = (63.9291 amu x 0.4861) + (65.9260 amu x 0.279) + (66.9271 amu x 0.041) + (67.9248 amu x 0.1875) + (69.9253 amu x 0.0062)
= 31.0862831 + 18.4274 + 2.740791 + 12.7192 + 0.4347916 
= 65.4084667 amu

Rounding to two decimal places, the atomic mass is 65.38 amu.

Zinc Has Five Naturally Occurring Isotopes, Zn-64, Zn-66, Zn-67, Zn-68