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Test Your Knowledge
Key Idea 1: Isotopes

1) All atoms of carbon have 6 protons, carbon-12 has __ neutrons and carbon-13 has __neutrons.

  1. 12 and 13
  2. 18 and 19
  3. 6 and 7
  4. They both have 6

2) A sample of magnesium, which contains a mixture of isotopes of magnesium-24, magnesium-25, and magnesium-26 atoms is analyzed with a mass spectrometer. How many peaks do you expect to see in the mass spectrum?

  1. 1
  2. 25
  3. 75
  4. 3
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D.

3) You detect a peak on a mass spectrum of a pure monatomic element near m/z: 28. Which isotope would you expect that this peak represents?

  1. Silicon-28 (A: 28 Z: 14)
  2. Nickel-58 (A: 58 Z: 28)

4) You insert a sample consisting of aluminum-27 atoms into a mass spectrometer. These atoms lose one electron each to become cations. At what mass/charge ratio do you expect to see a peak in the mass spectrum?

  1. m/z: 26
  2. m/z: 27
  3. m/z: 28
  4. m/z: 13
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B.

5) Which of the following isotopes is consistent with the knowledge that a particular atom has 7 protons and 8 neutrons? Consult the IUPAC Periodic Table of the Elements and Isotopes Learning Tool if needed.

  1. Nitrogen-8
  2. Oxygen-15
  3. Oxygen-8
  4. Nitrogen-15

6) Sulfur-36 and argon-36:

  1. Have the same mass number and have the same number of neutrons
  2. Have the same mass number and do not have the same number of neutrons
  3. Have the same atomic number and have the same number of neutrons
  4. Have the same atomic number and do not have the same number of neutrons
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B.
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