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Which Statement Is True at STP? (The Atomic Mass of Zn Is 65.39 U.)
Atomic mass is an essential property used to describe and compare different elements and compounds. It represents the average mass of an atom of an element, taking into account its isotopes and their abundance. One such element is zinc (Zn), which has an atomic mass of 65.39 U (unified atomic mass units) at standard temperature and pressure (STP). Let’s explore what STP means and delve into the significance of the atomic mass of Zn.
STP refers to standard temperature and pressure conditions commonly used in scientific calculations and experiments. At STP, the temperature is set at 0 degrees Celsius (273.15 Kelvin), and the pressure is maintained at 1 atmosphere (atm) or 101.3 kilopascals (kPa). These conditions provide a common reference point for scientists to compare and evaluate various properties of substances.
The atomic mass of Zn, 65.39 U, represents the average mass of an atom of zinc. This value takes into account the different isotopes of zinc found in nature, each with its own atomic mass and abundance. Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons. The atomic mass is calculated by considering the mass of each isotope and its relative abundance.
Zinc has five stable isotopes: Zn-64, Zn-66, Zn-67, Zn-68, and Zn-70. The most abundant isotope, Zn-64, has a mass of 63.929 U and an abundance of approximately 48.6%. Zn-66, Zn-67, Zn-68, and Zn-70 have masses of 65.926 U, 66.928 U, 67.927 U, and 69.925 U, respectively, with abundances ranging from 27.9% to 4.1%. By considering the mass and abundance of each isotope, the average atomic mass of zinc is determined to be 65.39 U.
FAQs:
Q: What is the significance of atomic mass?
A: Atomic mass helps us identify and compare different elements by providing a standardized value for their mass. It is used in chemical calculations, such as determining the amount of a substance in a reaction or calculating the molar mass of a compound.
Q: Why is atomic mass given in unified atomic mass units (U)?
A: Unified atomic mass units provide a convenient scale for comparing the masses of atoms. One unified atomic mass unit is defined as 1/12th the mass of a carbon-12 atom, which is approximately equal to the mass of a proton or neutron.
Q: How is atomic mass calculated?
A: Atomic mass is calculated by multiplying the mass of each isotope by its relative abundance and summing these values. The result represents the weighted average mass of all the isotopes present in a naturally occurring sample of an element.
Q: Does the atomic mass of an element change?
A: The atomic mass of an element does not change; however, it may vary slightly depending on the sample source due to variations in the abundance of isotopes.
In conclusion, at STP, the atomic mass of zinc is 65.39 U. This value represents the average mass of an atom of zinc, taking into account the different isotopes and their abundances. Atomic mass is a crucial property used to compare and analyze elements and compounds, providing a standardized scale for their masses. Understanding atomic mass helps scientists in various fields, including chemistry, physics, and materials science, to study and manipulate matter effectively.
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