Atomic structure, analysis and quantitative chem.

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  • Atomic structure, analysis and quantitative chem.
    • The masses and charges of protons, neutrons and electrons.
      • Protons= 1, neutrons= 1, electrons= 1/2000
    • Protons + neutrons= mass number
    • Isotopes are atoms of the same element with different numbers of neutrons.
    • The relative atomic mass of an element (Ar) compares the mas of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element.
    • The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
    • The Mr of calcium chloride = Ar of Ca= 40, Ar of Cl= 35.5, so Mr= 40+ (35.5*2)= 111
    • Benefits of using instrumental methods to detect and ID elements and compounds.
      • They provide fast, accurate and sensitive ways of analysing chemical substances.
      • compounds in a mixture can be separated using gas chromatography.
      • Once separated, compounds can be identified using a mass spectrometer
      • the mass spectrometer can be used to find the relative molecular mass of a compound from its molecular ion peak.
    • Paper chromatography
      • Foods can be checked by chemical analysis to ensure safe additives have been used. Paper chromatography and mass spectrometry are used here.
      • It can be used to analyse artificial colours in food.
    • Gas chromatography linked to mass spectroscopy (GC-MS)
      • The output from the gas chromatography column can be linked directly to a mass spectrometer
      • The mass spectrometer gives further data that a computer can use quickly to identify the individual compounds.
      • The mass spectrometer can be used to identify the Mr of a compound from its molecular ion peak.
    • The percentage of an element within a compound.
      • percentage of carbon in carbon dioxide, CO2= Ar of C= 12, Ar of O= 16. Mr of CO2= 12+ (16*2)= 44 so % of carbon= (12/44)* 100= 27.3%
  • Protons= 1, neutrons= 1, electrons= 1/2000

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