chemistry - 3e - volumetric analysis Flashcards
What is a standard solution?
A solution of accurately known concentration.
How can standard solution be prepared?
weighing a primary standard accurately
dissolving in a small volume of solvent (usually deionised or
distilled water) in a beaker
transferring the solution and rinsings into a volumetric flask
making up to the graduation mark with solvent
stoppering and inverting
What is another way of preparing standard solutions?
By accurate dilution by
pipetting an appropriate volume of a standard solution into a
volumetric flask, making up to the graduation mark with solvent, stoppering and inverting.
What must a primary standard be?
- be available in a high state of purity
- be stable when solid and in solution
- be soluble
- have a reasonably high GFM
What are some 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?
As it has a relatively low
GFM, is unstable as a solid (absorbs moisture) and unstable as a solution.
What must happen to sodium hydroxide before being used in volumetric analysis?
It must be standardised.
What is EDTA?
An important complexometric reagent and can be used to determine the concentration of metal ions in solution.
What are back titrations used for?
To find the number of moles of a substance by reacting it with an excess volume of a reactant of known concentration.
In a back titration, what happens to the resulting mixture?
It is then titrated to work out
the number of moles of the reactant in excess.
When is a back titration useful?
When trying to work out the quantity of substance in a solid with a low solubility.