Chapter 2: Problem 17
Chlorine consists of two isotopes, chlorine- \(35(75.77 \%\) abundance) and chlorine- 37 ( \(24.23 \%\) abundance). Draw a graph of the mass spectrum obtained from a sample of \(\mathrm{Cl}_{2}\) gas.
Short Answer
Expert verified
Graph peaks at masses 70, 72, and 74 with respective intensities 57.44%, 36.72%, and 5.87%.
Step by step solution
01
Identify Isotopes and Their Abundances
Chlorine has two isotopes: chlorine-35 with 75.77% abundance and chlorine-37 with 24.23% abundance. These percentages will help us find the relative peaks in the mass spectrum.
02
Calculate Relative Intensities for Single Chlorine Atoms
For a single chlorine atom, the isotopes show peaks at their respective mass numbers, 35 and 37, with intensities proportional to their abundances. Thus, for chlorine-35, the intensity is 75.77, and for chlorine-37, it is 24.23.
03
Identify Possible \\( ext{Cl}_2\\) Molecule Combinations
In a sample of \( ext{Cl}_2\) gas, the molecule can consist of a combination of the isotopes: 35-35, 35-37, and 37-37. We need to calculate the masses for these combinations.
04
Calculate Masses of the \\( ext{Cl}_2\\) Molecules
The molecular masses of the \( ext{Cl}_2\) gas combinations are: 70 for 35-35, 72 for 35-37, and 74 for 37-37. These reflect the sum of atomic masses of the chlorine atoms in each pair.
05
Calculate Relative Abundances for Each Molecule
Use the formula \(\text{Relative abundance} = (\text{Abundance of first isotope}) \times (\text{Abundance of second isotope})\). For Cl-35/Cl-35: \(75.77\% \times 75.77\% = 57.44\%\); for Cl-35/Cl-37: \(2 \times 75.77\% \times 24.23\% = 36.72\%\); and for Cl-37/Cl-37: \(24.23\% \times 24.23\% = 5.87\%\). The 2 multiplier in the second calculation accounts for the two possible arrangements.
06
Draw the Mass Spectrum
On the x-axis, plot the masses (70, 72, 74) and on the y-axis, plot their respective calculated relative abundances. So, points are at (70, 57.44%), (72, 36.72%), and (74, 5.87%). Ensure proper scaling to reflect the difference in abundance clearly where the peak at 70 is the highest and 74 is the lowest.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Isotopic Abundance
Isotopic abundance refers to the percentage of a particular isotope present in a natural sample of an element. For chlorine, which has two stable isotopes, the isotopic abundance helps determine the characteristics observed in mass spectrometry.
- Isotopic Contribution: Chlorine-35 represents 75.77% of the natural mixture, while chlorine-37 consists of 24.23%.
- Mass Spectrum Peaks: The peaks in a mass spectrum directly reflect these isotopic abundances. Higher abundance results in taller peaks for each isotope.
Chlorine Isotopes
Chlorine's two main isotopes are chlorine-35 and chlorine-37. These isotopes differ in the number of neutrons, which affects their mass. Here's how they influence the mass spectrum:
- Chlorine-35: This isotope has a mass number of 35. Due to its higher abundance, it plays a major role in the mass spectrum of chlorine gas.
- Chlorine-37: With a mass number of 37, this isotope is less abundant. Its peak in the spectrum is smaller compared to chlorine-35.
Chlorine Gas Analysis
Analyzing chlorine gas through mass spectrometry reveals information about the molecular composition and isotopic distribution.
- Molecular Combinations: Chlorine gas molecules can be a mix of the isotopes, forming combinations like 35-35, 35-37, and 37-37.
- Mass Calculations: These combinations result in distinct mass peaks, calculated as 70 (35-35), 72 (35-37), and 74 (37-37).
- Relative Abundances: The relative abundance is calculated using the product of the isotopic abundances. For instance, 35-35 has the highest, while 37-37 has the lowest occurrence.