What is the average atomic mass of zinc?
The correct answer and explanation is:
The average atomic mass of zinc is approximately 65.38 u (unified atomic mass units).
The atomic mass of an element represents the weighted average of the masses of all naturally occurring isotopes of that element. Zinc has five stable isotopes: ^64Zn, ^66Zn, ^67Zn, ^68Zn, and ^70Zn, each with different relative abundances and atomic masses. To calculate the average atomic mass, you must consider both the mass of each isotope and its abundance in nature.
- ^64Zn has an atomic mass of approximately 63.929 u and accounts for about 48.6% of naturally occurring zinc.
- ^66Zn has an atomic mass of approximately 65.926 u and makes up about 27.9% of the natural zinc.
- ^67Zn has an atomic mass of approximately 66.927 u and constitutes around 4.1% of zinc.
- ^68Zn has an atomic mass of approximately 67.925 u and is about 18.8% of the natural zinc.
- ^70Zn has an atomic mass of approximately 69.925 u and makes up about 0.6% of naturally occurring zinc.
To find the average atomic mass of zinc, multiply the atomic mass of each isotope by its relative abundance (as a decimal) and then sum these values: (63.929×0.486)+(65.926×0.279)+(66.927×0.041)+(67.925×0.188)+(69.925×0.006)(63.929 \times 0.486) + (65.926 \times 0.279) + (66.927 \times 0.041) + (67.925 \times 0.188) + (69.925 \times 0.006)
The result is approximately 65.38 u, which is the average atomic mass of zinc.
This average value is what is typically used in chemical calculations. It reflects the distribution of isotopes in nature and allows for a more accurate representation of the element’s mass in reactions and other applications.