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Ch.2 - Atoms, Molecules & Ions
Chapter 2, Problem 133

Use the data from the mass spectrum of a sample of an element to calculate the element's atomic weight. Identify the element.

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1
Identify the isotopes present in the mass spectrum and their respective abundances.
For each isotope, multiply the mass of the isotope by its relative abundance (expressed as a decimal).
Sum the values obtained from the previous step to get the weighted average mass, which is the atomic weight of the element.
Compare the calculated atomic weight with known atomic weights from the periodic table to identify the element.
Verify the identification by checking if the isotopic composition matches the natural abundance of the element's isotopes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio of ions. It provides information about the different isotopes of an element and their relative abundances. By analyzing the peaks in the spectrum, one can determine the mass of the isotopes and their proportions, which are essential for calculating the average atomic weight of the element.
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Atomic Weight Calculation

The atomic weight of an element is calculated by taking the weighted average of the masses of its isotopes, based on their natural abundances. This involves multiplying the mass of each isotope by its relative abundance (expressed as a fraction) and summing these values. The result gives a single value that reflects the average mass of an atom of the element as it occurs in nature.
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Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For example, carbon has isotopes like carbon-12 and carbon-14. Understanding isotopes is crucial for interpreting mass spectra, as the presence of multiple isotopes affects the calculated atomic weight and helps in identifying the element.
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