Quantitative Chemistry

• The Law of Conservation of Mass - no atoms are made or lost during a chemical reaction
• Sometimes reactions appear to involve a change in mass:

  When the mass of a gaseous product or reactant that has not been considered in a non-closed system.
• A closed system is one from which nothing can escape, including gases
• Uncertainty is always present when measurements are made
• Uncertainty can be expressed as a range about the mean
• Limiting reactants are used with other reactants in excess to ensure that all of the reactant is used up
• One mole of any gas occupies the same volume at the same temperature and pressure
• Room temperature and pressure are 20 degrees Celsius and 1 atmosphere (atm)
• At room temp and pressure, one mole of any gas occupies 24dm(threed)
• A strong acid is completely ionised in aqueous solution. Examples include:

  • HCl
  • HNO3
• The pH of strong acids are lower than weak acids, at pH 1-2
• A weak acid id only partially ionised in aqueous solution
• The pH of weak acids is higher than strong acids but below 7.

  Examples include:

  • ethanoic
  • citric
  • carbonic
• As the pH decreases by 1 unit, the concentration of H+ increases x 10
• The practical technique for finding the volume of one solution that is needed to completely react with another is called titration.
• The technique of titration is often used to calculate:

  • The volume of one solution that is needed to completely react with another
  • The unknown concentration of an acid or alkali
• A dilute solution is one where a small amount of solution is added to a large amount of water
• A concentrated solution us one where lots of solute is added to a small amount of water
• The concentration of a solution can be measured in two ways:

  • $mol/dm^3$
  • $g/dm^3$
• The number of cm3 in one dm3 is 1000
• you can interconvert from mol/dm3 and g/dm3 like this:

  • g/dm3 = mol x Mr/dm3
  • mol/dm3 = (mass/Mr)/dm3