We would expect three “kinds” of H2 molecules 1H1H, mass = 2.0 u,

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Presentation transcript:

We would expect three “kinds” of H2 molecules 1H1H, mass = 2.0 u, QUESTION: A sample of H2 molecules, containing protium (1H) and deuterium (2H) isotopes, is injected into a mass spectrometer. How many signals due to H2+ ions can we expect to observe? A. 0, B. 1, C. 2, D. 3 We would expect three “kinds” of H2 molecules 1H1H, mass = 2.0 u, 1H2H, mass = 3.0 u, 2H2H, mass = 4.0 u Therefore, we also expect three kinds of “H2+” ions. A sample of H2 molecules, containing protium and deuterium isotopes, is fed into a mass spectrometer. How many signals due to H2 ions with a +1 charge can we expect to observe? A. 0, B. 1, C. 2, D. 3 PAUSE We would expect to find three kinds of H2 molecules. One kind would be made up of two protium atoms, which will have a total mass of 2 atomic mass units, since each protium atom has a mass of 1 unit. Another kind would be made up of a protium atom and a deuterium atom, which will have a total mass of 3 atomic mas sunits. And a third kind would be made up of two deuterium atoms. Therefore, we also expect to see three dihydrogen ions. Each kind will correspond to one signal in the mass spectrometer output. The correct answer is D. CLICK CONTINUED ON NEXT PAGE

http://upload. wikimedia http://upload.wikimedia.org/wikipedia/commons/b/b8/Mass_spectrometer_schematics.png Here’s a schematic of what happens in a mass spectrometer. HIGHLIGHT pertinent sections of diagram as they are mentioned A gas sample is introduced in to the instrument. The molecules in the gas are ionized… and a beam of positive ions is produced inside the instrument. The beam of ions is passed through a magnetic field. For ions of the same charge, the path of lighter ions are bent more than those of heavier ions. Ions with the same mass-to-charge ratio will reach the detector in the same place, and produce one signal. In this diagram shown here, the beam corresponding to ions with a mass of 44 units are bent more than the beam correspnoding to ions with a mass of 46 units. CLICK PAUSE END RECORDING

Video ID: 1-12-2 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08