C2 amount of substance

• relative atomic mass is the average mass of an atom of an element, relative to 1/12 the mass of a carbon-12 atom
• relative molecular mass is the average mass of a molecule, relative to 1/12 the mass of a carbon-12 atom
• relative formula mass is the relative mass of an ionic compound as this does not exist as a molecule
• the avogadro constant is the number of atoms/particles in one mole of a substance
• the avogadro constant is 6.022 x 10^23
• a mole is the amount of substance that contains 6.022*10^23 atoms/particles
• moles = mass / Mr
• concentration represents how much solute is dissolved in a known volume of solution, it is measured in moldm^-3
• concentration = moles / volume
• the ideal gas equation is pV=nRT
• in pV=nRT:

  p = pressure in Pa

  V = volume in m^3

  n = number of moles

  R = gas constant, 8.31

  T = temperature in K
• no gases obey the ideal gas equation exactly, so no real gases are ideal gases
• the empirical formula is the simplest whole number ratio of atoms of each element in a compound
• to find empirical formula, draw a table:

  • first row write masses or percentage by mass
  • second row write Mr
  • third row use moles = mass / Mr to write moles
  • fourth row divide by the smallest
  • scale up to get integers
• the molecular formula is the actual number of atoms of each element in a compound
• to find the molecular formula, divide the Mr of the compound by the Mr of the empirical formula, then multiply the empirical formula by this value
• chemical equations need to be balanced before you can use them in calculations
• rules for balancing equations:

  • do not change any of the formulae
  • only add coefficients, no other numbers
  • coefficient represents number of moles of that substance
  • if the equation is ionic, the charges on each side must also be balanced
• atom economy = (mass of desired product / total mass of reactants) * 100
• a high atom economy means less waste is produced, making it more economically viable
• percentage yield = (experimental yield / theoertical yield) * 100
• a high percentage yield means less product has been lost throughout the manufacture process