Chemistry module 2.2

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    • OCR A Level Chemistry
    • Contents
      • 2.2.1 Amount of Substance
      • 2.2.2 Determining Formulae
      • 2.2.3 Reaction Calculations
      • 2.2.4 The Ideal Gas Equation
      • 2.2.5 Percentage Yield & Atom Economy
    • Your notes
    • Amount of substance
      The name given when counting the number of particles in a substance
    • Amount of substance
      Often seen in calculations using the letter / symbol n
    • Units for amount of substance
      moles / mol
    • Avogadro constant, N
      The number of particles equivalent to the relative atomic, molecular or formula mass of a substance
    • The Avogadro constant applies to atoms, molecules, ions and electrons
    • Value of N
      6.02 x 10^23 g mol^-1
    • Mass of a substance with this number of particles
      A mole (mol)
    • Molar mass
      The mass of substance that contains the same number of fundamental units as exactly 12.00 g of carbon-12
    • Relationship between amount of substance, n, mass, m, and molar mass, M
      n = mass, m / Molar mass, M
    • Molar gas volume
      The volume occupied by one mole of any gas, at room temperature and pressure
    • Molar volume
      Equal to 24 dm^3
    • One mole of any element is equal to the relative atomic mass of the element, in grams
    • One mole of carbon is 6.02 x 10^23 atoms of carbon with a mass of 12.0 g
    • One mole of water is 6.02 x 10^23 molecules of water with a mass of 18.0 g
    • Calculating molar mass and molar gas volume
      1. Calculate the molar mass of: a. Carbon dioxide, CO2 b. Magnesium nitrate, Mg(NO3)2
      2. Calculate the number of moles of each gas: a. 36.0 dm^3 of carbon monoxide, CO b. 9.6 dm^3 of chlorine, Cl2
    • Molecular formula
      Shows the number and type of each atom in a molecule
    • Empirical formula
      Shows the simplest whole number ratio of the elements present in one molecule of the compound
    • The empirical formula of ethanoic acid is CH2O
    • The molecular formula of ethanoic acid is C2H4O2
    • Deducing molecular & empirical formulae
      Deduce the molecular and empirical formula of the following compounds:
    • Calculating empirical formula from mass
      Determine the empirical formula of a compound that contains 10 g of hydrogen and 80 g of oxygen.
    • Calculating empirical formula from percentage composition
      Determine the empirical formula of a compound that contains 85.7% carbon and 14.3% hydrogen.
    • Calculating molecular formula
      The empirical formula of X is CH2 and the relative molecular mass of X is 180.2. What is the molecular formula of X?
    • Water of crystallisation
      When some compounds can form crystals which have water as part of their structure
    • Hydrated compound

      A compound that contains water of crystallisation
    • Anhydrous compound

      A compound which doesn't contain water of crystallisation
    • Cobalt(II) chloride can be hydrated by six or two water molecules: CoCl2·6H2O or CoCl2·2H2O
    • Calculating water of crystallisation
      10.0 g of hydrated copper sulfate are heated to a constant mass of 5.59 g. Calculate the formula of the original hydrated copper sulfate.
    • Reacting masses

      The masses of reactants are useful to determine how much of the reactants exactly react with each other to prevent waste
    • Mass calculation using moles
      Calculate the mass of magnesium oxide that can be made by completely burning 6 g of magnesium in oxygen.
    • Moles
      The amount of a substance, measured in mol
    • Molar mass
      The mass of one mole of a substance, measured in g mol−1
    • Formula unit
      The smallest repeating unit of a compound
    • One mole of CaF2 contains one mole of CaF2 formula units, but one mole of Ca and two moles of F ions