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mass spec - Chemistry in Context Life on Mars The Viking...

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Chemistry in Context Life on Mars. The Viking and Phoenix landers were sent to Mars to determine if life ever existed there. What were these spacecrafts looking for and how did they perform the analyses?
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CH 11 Mass Spectrometry HW: 11-2, 11-3, 11-6, 11-7, 11-8, 11-11 Concept Te$t The 12.01 on the periodic table for C indicates that: (A) A carbon atom weighs 12.01 g (B) A carbon atom weighs 12.01 lbs (C) A carbon atom weighs 12.01 x 10 -24 g (D) It does not indicate anything pertaining to the absolute mass of a carbon atom
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CH 11 Mass Spectrometry What is atomic mass? Atomic mass units (amu) or daltons (Da): Defined relative to 12 C, which is assigned a mass of exactly 12 amu. H has a mass of 1.008 relative to carbon-12, so it is assigned a mass of 1.008 amu. 1 amu = 1 Da = an absolute mass of 1.6605387 x 10 -27 kg The mole provides the link between numbers of atoms and mass of atoms. It is defined as the amount of a substance that contains the same number of entities as there are atoms in exactly 12 g of C-12. This number is Avogadro’s number.
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CH 11 Mass Spectrometry Mass to charge ratio A unitless ratio of mass number to the number of charges, z, on the ion. For 12 C 1 H 4 + the m/z is 16.0313/1. For 13 C 1 H 4 2+ the m/z is 17.0346/2 = 8.5173. Ions in mass spec are often singly charged so the z is frequently dropped, but this is not strictly correct. A mass spectrometer is an instrument that produces ions and separates them according to their mass-to-charge ratios, m/z.
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CH 11 Mass Spectrometry General steps (1) Atomization (2) Ionization (3) Separation of ions (4) Detection-Counting the ions General Schematic 10 -5 – 10 -8 Torr Inlet Mass Analyzer
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Mass Spectra M : ionize M + . fragment m 1 + + m 2 …. Where M is a molecule and m x fragments of M
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Mass Spectra Molecular Ion: Unfragmented molecule that has lost an electron Base Peak: Highest intensity peak Fragment Ions: Stable carbocations of the parent molecule. *Key Concepts
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Mass Spectra Notice the successive loss of m/z = 14. This corresponds to fragments of the molecular ion that have lost CH 2 .
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Mass Spectra
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Concept Test The spectrum below is from a hydrocarbon containing which substituent?
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