4.5 volumetric analysis Flashcards
what is a standard solution
a solution of accurately known concentration
how can you prepare a standard solution
- weigh a primary standard accurately
- dissolve in a small amount of solvent (usually distilled water) in a beaker
- transfer the solution and rinsings into a volumetric flask
- make up to the graduation mark with more solvent
- stop and invert
how can you prepare a standard solution using accurate dilution
- pipette an appropriate volume of a standard solution into a volumetric flask
- make up to the graduation mark with solvent
- stop and invert
what qualities must a primary standard have
- available in a high state of purity
- be stable when solid and in solution
- be soluble
- have a reasonably high GFM
what are examples of primary standards
sodium carbonate
hydrated oxalic acid
potassium hydrogen phthalate
silver nitrate
potassium iodate
potassium dichromate
why is sodium hydroxide not a primary standard
it has a low gfm
its unstable when solid
its unstable when solution
has to be standardised before it can be used in volumetric analysis
what are redox titrations based on
reactions between oxidising and reducing agents
what are complexometric titrations based on
reactions in which complexes are formed
what is EDTA
it is an important complexometric reagent and can be used to determine the concentration of metal ions in solution
what are back titrations used for
finding the number of moles of a substance
how do back titrations work
reacting substance with excess volume of a reactant of known concentration
the resulting mixture is titrated to work out the number of moles of the reactant is in excess
from the initial number of moles of that reactant the number of moles used in the reaction can be determined
the initial number of moles of the subtance being analysed can then be calculated
when is a back titration useful
when you are trying to work out the quantity of a substance in a solid with a low solubility
