Quantitative Chemistry

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  • Quantitative Chemistry
    • Atomic Mass
      • Protons + Neutrons = Mass Number
      • Isotopes
        • Same number of protons (atomic number)
        • Different number of neutrons (mass number)
        • Same element
          • Different number of neutrons (mass number)
          • Same number of protons (atomic number)
      • Relative Formula Mass (Mr)
        • = sum of  all (Mr)s
        • e.g. Mr for MgCl? = 95
    • Moles
      • Mr of substance in grams is known as one mole
      • Number of moles = Mass in g of element ÷ Mr of element
    • Percentage mass
      • = (mass of element in compound ÷ total Mr of compound)  x 100
      • e.g. % mass of sodium in sodium carbonate
        • (23x2  ÷ 106) x 100 = 43.4%
    • Empirical Formula
      • List all elements in compound
        • Write amount in question
          • Divide by Ar for that element (gives moles)
            • Divide each by smallest number if moles
    • Mass of Reactants
      • e.g.  If we have 50g of CaCO3, how much CaO can we make?
        • Work out the Mr values for the two compounds
          • Mr of CaCO3 = 100
          • Mr of CaO = 56
    • Percentage Yield
      • = (amount made ÷ predicted yield) x 100
      • Never 100%
        • Impurities
        • Other reactants
        • Difficult to separate
        • Reversible reaction
    • Reversible reactions
      • Products of reaction can react to produce original products
      • e.g. ammonium chloride ? ammonia + hydrogen chloride
    • Analysing Substances
      • Chromatography
        • Paper
        • Gas (GC-MS)
          • Separates mixture of compounds
          • Substances travel through tube at different speeds so become separated
          • No. of peaks on gas chromatograph shows no. of different compounds present
          • Position of peaks shows retention time for each substance
          • Can be linked to mass spectronometer
            • Sensitive
            • Fast
            • Accurate
      • Mass Spectronomy
        • Finds Mr of moelcule
  • 100 g of CaCO3 would yield 56 g of CaO
    • Mr of CaO = 56
    • Mr of CaCO3 = 100
    • Therefore, 50g of CaCO3 makes 28g of Cao

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