How Much?

  • Created by: DeanJowl
  • Created on: 06-11-12 20:18
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  • How Much?
    • The mass of atoms
      • The relative mass of protons and neutrons is 1.
      • The atomic number of an atom is its number of protons.
      • The mass number of an atom is the total number of protons and neutrons in the necleus.
      • Isotopes are atoms of  the same element with different numbers  of neutrons.
    • Masses of atoms and Moles
      • We compare the masses of atoms by measuring them relative to atoms of Carbon-12
      • We worl out the relative formula mass of a compound by adding up the relative atomic masses of the elements in it, in the ratio shown by its formula.
      • One mole of any substance is its relative formula mass, in grams.
    • Percentages and formulae
      • The relative atomic masses of the elements in a compound and its formula can be used to work out its percentage composition.
      • We can calculate empirical formulae given the masses or percentage composition of elements present.
    • Equations and calculations.
      • Balanced symbol equations tell us the number of moles of substance involved in a chemical reaction.
      • We can use balanced symbol equations to calculate the masses of reactants and products in a chemical reaction.
    • The yield of a chemical reaction.
      • The yield of a chemical reaction describes how much product is made.
      • The percentage yield of a chemical reaction tells us how much product is made compared with the maximum (100%).
      • Factors affecting the yield of a chemical reaction include product being left behind in the apparatus and difficulty separating the products from the reaction mixture.
      • It's important to get the highest yield and minimise energy wasted to benefit the environment.
    • Reversible reactions
      • In a reversible reaction  the products of the reaction can react to make the original reactants.
      • The reaction can be shown to be reversible by using a
    • Analysing substances
      • Although simpler to use than bench chemistry methods, instrumental methods still need trained technicians to operate.
      • Additives may be added to food in order to improve its appearance , taste and its 'shelf life'.
      • Food scientists can anaylse foods to identify additives.
      • Modern instrumental techniques provide fast, accurate and sensitive ways of analysing chemical substances.
    • Instrumental analysis.
      • Compounds in a mixture can be seperated 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.


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