1.4 -1.5 - The Mole, Solutions, & Ideal gases

• Absolute zero


  temperature at which all movement of particles stop
• If pressure remains the same 


  Volume/Temperature = constant
• if constant pressure and temperature


  Volume/moles = constant
• The mole


  A mole of a substance is the amount of the substance that contains as may specified particles as there are atoms in exactly 12g of carbon-12
• Relative molecular mass


  Only applies to molecular substances: the mass of a molecule relative to 1/12 the mass of a cabon-12 atom
• Relative formula mass


  the sum of the relative atomic masses of the atoms as given in the chemical formula of a species
• Relative atomic mass


  the weighted average of the elements isotopic masses relative to 1/12 the mass of a carbon-12 atom
• Empirical formula 


  gives the simplest ratio of atoms of each element present in that compound
• Molecular formula


  • gives the actual number of atoms of each element present in that compound
  • only used for covalent molecular species
• To find molecular formula:

  • relative molecular mass (or molar mass)
  • divided by the relative empirical formula mass
• The concentration of a solution is a description of the relative amounts of solute and solvent present
• Concentrated solution


  contains a lot of solute relative to the amount of solvent
• Dilute solution 


  contains little solute relative to the amount of solvent
• molar concentration:

  • also known as molarity
  • the concentration of a solution measured in mol/dm^3
• Concentration of components of a solution:

  • if an ionic compound is soluble, when it dissolves, the ions are said to dissociate
• Dilution:

  • the process of adding more solvent to a solution
  • number of moles stays the same
  • volume changes
• Relative atomic mass


  the weighted average mass of of the atoms relative isotopic masses relative to 1/12 of a carbon-12 atom
• Molecules

  covalent substances only
• A mole


  the amount of substance that contains as many specified particles as there are atoms in exactly 12g of carbon-12
• Percentage composition of a compound (by mass)


  indicates what proportion of the total mass of the compound is accounted for by the mass of each element
• Compound


  a pure substance that consists of two or more types of elements chemically combined in a whole number ratio of atoms
• • for metallic substances the empirical formula is the same as the symbol of the element
  • for ionic substances the empirical formula is the same as the ionic formula
  • metallic and ionic substances DO NOT have a molecular formula
• Molar concentration


  determined by the amount of solute and the volume of the solution
• Preparing a solution of known concentration:

  1. dispense the required mass of a solid into a weighing bottle
  2. Record the mass of the weighing bottle and solid on an analytical balance
  3. transfer the solid to a volumetric flash using a funnel
  4. record the mass of the empty weighing bottle
  5. add deionised water to the volumetric flask via the funnel until it is about 1/3 full
  6. put a stopper on the flask and shake it until the solid dissolves
  7. fill the flask to the calibration mark with deionised water, the meniscus should sit on the line
  8. put a stopper on the flask and invert several times
• Ideal gases:

  • consists of moving particles with negligible volume and no intermolecular forces
  • all collisions between particles are perfectly elastic
• The molar volume of an ideal gas is a constant at specific temperature and pressure
• Real gases deviate from ideal gas behaviour most:

  • when pressure is high
  • when temperature is low
  • when the gas molecules are polar and strongly attracted to each other
  • when the gas molecules are large
• Avogrado's hypothesis 


  equal volumes of all gases at the same temperature and pressure contain the same number of molecules
• Molar volume


  the volume occupied by one mole of gas at a specified temperature and pressure

  • at STP Vm is 22.7 dm^3/mol
• Preparing a solution of known concentration


  1. dispense the required mass of the solute into the volumetric flask
  2. Fill the flask with deionised water until 1/3, stopper the flask and shake until the solid dissolves
  3. Fill the flask with deionised water until the calibration mark
  4. Stopper the flask and invert several times
• if an ionic compound is soluble, when it dissolves, the ions are said to dissaociate