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Ch.2 - Atoms, Molecules, and Ions
Chapter 2, Problem 38b

Consider the mass spectrometer shown in Figure 2.11. Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (b) The height of each peak in the mass spectrum is inversely proportional to the mass of that isotope.

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1. Understand the concept of a mass spectrometer: A mass spectrometer is an instrument that is used to identify the different kinds of isotopes present in a sample of an element. It does this by ionizing the atoms in the sample and then accelerating them through a magnetic field. The ions are deflected by the magnetic field to different extents depending on their mass-to-charge ratio. The ions are then detected and the relative abundance of each isotope is determined.
2. Analyze the statement: 'The height of each peak in the mass spectrum is inversely proportional to the mass of that isotope.' This statement is suggesting that the heavier an isotope is, the smaller the peak in the mass spectrum will be.
3. Evaluate the statement: The height of each peak in the mass spectrum is actually representative of the relative abundance of each isotope in the sample, not the mass of the isotope. Therefore, the statement is false.
4. Correct the statement: A more accurate statement would be 'The height of each peak in the mass spectrum is proportional to the relative abundance of that isotope in the sample.'
5. Remember: The position of the peak in the mass spectrum (along the x-axis) is determined by the mass-to-charge ratio of the isotope, not the height of the peak (along the y-axis).

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Key Concepts

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

Mass Spectrometry

Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. It involves ionizing chemical species and sorting the ions based on their mass. The resulting mass spectrum provides information about the composition and abundance of different isotopes in a sample.
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Isotope Abundance

Isotope abundance refers to the relative amount of each isotope of an element present in a sample. In mass spectrometry, the height of each peak in the mass spectrum corresponds to the abundance of the respective isotope, with taller peaks indicating higher abundance, not inversely proportional to mass.
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Mass Spectrum Interpretation

Interpreting a mass spectrum involves analyzing the peaks to determine the identity and relative abundance of isotopes. The position of each peak indicates the mass of the isotope, while the height reflects its abundance. Therefore, the statement in the question is false; peak height is directly proportional to isotope abundance, not inversely related to mass.
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Guided course
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Electromagnetic Spectrum
Related Practice
Textbook Question

Rubidium has two naturally occurring isotopes, rubidium-85 (atomic mass = 84.9118 amu; abundance = 72.15%) and rubidium-87 (atomic mass = 86.9092 amu; abundance = 27.85%). Calculate the atomic weight of rubidium

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Textbook Question

(a) Thomson's cathode-ray tube (Figure 2.4) and the mass spectrometer (Figure 2.11) both involve the use of electric or magnetic fields to deflect charged particles. What are the charged particles involved in each of these experiments?

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Textbook Question

Consider the mass spectrometer shown in Figure 2.11. Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (a) The paths of neutral (uncharged) atoms are not affected by the magnet.

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Textbook Question

Massspectrometry is more often applied to molecules than to atoms. We will see in Chapter 3 that the molecular weight of a molecule is the sum of the atomic weights of the atoms in the molecule. The mass spectrum of H2 is taken under conditions that prevent decomposition into H atoms. The two naturally occurring isotopes of hydrogen are 1H (atomic mass = 1.00783 amu; abundance 99.9885%) and 2H (atomic mass = 2.01410; abundance 0.0115%). (a) How many peaks will the mass spectrum have?

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Textbook Question

Massspectrometry is more often applied to molecules than to atoms. We will see in Chapter 3 that the molecular weight of a molecule is the sum of the atomic weights of the atoms in the molecule. The mass spectrum of H2 is taken under conditions that prevent decomposition into H atoms. The two naturally occurring isotopes of hydrogen are 1H (atomic mass = 1.00783 amu; abundance 99.9885%) and 2H (atomic mass = 2.01410; abundance 0.0115%). (c) Which peak will be the largest, and which the smallest?

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Textbook Question

For each of the following elements, write its chemical symbol, locate it in the periodic table, give its atomic number, and indicate whether it is a metal, metalloid, or nonmetal: (a) radon (b) tellurium (c) cadmium (d) chromium (e) barium (f) selenium (g) arsenic.

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