quantitative analysis

• concentration (mol dm^3 ) = moles (mol) / volume (dm^3)
• conversion from gdm3 to mol dm3

  gdm3 ->mol dm3

  • mass / Mr = moles

  mol dm3 -> gdm3

  • moles x Mr = mass
• CORE PRACTICAL 


  1. use a pipette and pipette filler to add 25 cm3 of dilute sodium hydroxide solution to a clean conical flask
  2. add a few drops of phenolphthalein indicator and put the conical flask on a white tile.
  3. fill the burette with dilute hydrochloric acid and note the starting volume
• CORE PRACTICAL


  1. slowly add the acid from the burette to the conical flask, swirling to mix
  2. stop adding the acid when the end-point is reached (when the colour first permanently changes from pink to colourless), note the final volume reading
  3. repeat steps 1 to 5 until you get concordant titres (see step 1 in the analysis)

  
• actual yield - quantity of product that is obtained from a chemical reaction, usually less than theoretical yield
• theoretical yield - the maximum possible mass of a product that a chemical reaction can make
• percentage yield = ( actual yield / theoretical yield ) x 100
• causes of actual yield being less than theoretical yield

  • incomplete reactions (not all of the reactants have reacted)
  • practical losses during the experiment (some product has been left in the weighing boat etc)
  • side reactions (some of the products react to form other products than those you wanted)
• atom economy - a measure of the amount of starting materials that end up as useful products
• important for sustainable development and for economic reasons to use reactions with high atom economy
• atom economy = ( Mr of desired product from reaction / sum of Mr of all reactants ) x100
• look for a high atom economy, high yield, fast rate, equilibrium position to the right (towards products) and useful by-products
• volume (dm3) of gas = mol x 24

  volume (cm3) of gas = mol x 24000
• a balanced equation, the mass/volume of a reactant and are asked to calculate the mass/volume of a product

  calculate moles of the reactant if given a mass

  -moles=mass ÷ molar mass

  -if given a volume: moles = volume ÷ 24

  • work out the mole ratio and so work out how many moles of the product you have
  • calculate mass/volume using moles for calculating mass, mass=moles x molar mass for calculating volume, volume=moles x 24
• avogadros law - one mole of a substance contains 6.02 x 1023 particles