quantitative chemistry

• the atom economy is the measure of the proportion of the starting reactants that end up as the desired products
• atom economy =

  • relative formula mass of desired products / relative formula masses of all the reactants
• concentration tells us the mass of a solute in a given volume of solution
• the law of conservation states that no atoms are lost or made during a chemical reaction, so the mass of the reactants equals the mass of the products
• the relative formula mass of a compound is the sum of all the relative atomic masses of the atoms in the proportions shown in the formula
• percentage by mass = (relative atomic mass of element / relative formula mass) X 100
• some reactions can appear to have a change in mass if a product or reactant is a gas, however this can be explained by the fact if a reactant or a product is a gas, it's mass cannot be taken into account
• uncertainty is plus or minus half the resolution
• the mass of one mole of a substance in grams numerically equal to its relative formula mass (mass = Mr X moles)
• the number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant (6.02 x 10 ^ 23 per mole)
• the limiting reactant is the reactant that is completely used up first, because once it is used up the chemical reaction can no longer continue so the amount of product produced is limited
• a smaller volume or a larger mass of solute gives a higher concentration
• a larger volume or a smaller mass of solute gives a lower concentration
• concentration = mass / volume
• it is not always possible to obtain maximum theoretical yield because:

  • the reaction may be reversible and so not go to completion
  • some product may be lost when it is separated from the reaction mixture
  • some reactant may react in different ways to the expected reaction
• the amount of product obtained is known as the yield
• % yield = (mass of product actually made / maximum theoretical mass) X 100
• atom economy and atom utilisation are the same thing
• the concentration of a solution can be measured in mol/dm3
• titration

  1. measure 25cm3 of the solution with the unknown concentration using a pipette and a pipette filler. Place into a conical flask
  2. add 5 drops of phenolphthalein indicator into conical flask
  3. place conical flask on white tile to ensure colour change can be seen clearly
  4. fill a burette with the solution with the known concentration to 0.0cm3
  5. slowly start the titration while continuously swirling the contents in the conical flask
  6. stop titration when indicator turns slightly pink
  7. read the final volume of known solution from the bottom of the meniscus
  8. repeat to concordant results
• in titration, the equation used is 'moles = concentration x volume'