4.5 Volumetric analysis Flashcards
1
Q
What must a primary standard be?
A
- be available in a high state of purity
- be stable when solid and in solution
- be soluble
- have a reasonably high GFM
2
Q
Give 6 examples of primary standards
A
- sodium carbonate Na2CO3
- hydrated oxalic acid H2C2O4.2H2O
- potassium hydrogen phthalate KH(C8H4O4)
- silver nitrate AgNO3
- potassium iodate KIO3
- potassium dichromate K2Cr2O7
3
Q
Why is sodium hydroxide not a primary standard?
A
- relatively low GFM
- unstable as a solid (absorbs moisture)
- Unstable as a solution
4
Q
What must happen to sodium hydroxide before being used in volumetric analysis?
A
It must be standardised
5
Q
What happens during back titrations?
A
- used to find the number of moles of a substance by reacting it with an excess volume of reactant of known concentration
- The resulting mixture is then titrated to work out the number of moles of the reactant in excess
- From the initial number of moles of that reactant, the number of moles used the reaction can be determined
- The initial number of moles of the substance being analysed can then be calculated
6
Q
When is a back titration useful?
A
when trying to work out the quantity of substance in a solid with a low solubility
7
Q
What is EDTA and what is its use?
A
- It is an important complexometric reagent and can be used to determine the concentration of metal ions in solution
8
Q
What is a standard solution?
A
a solution of accurately known concentration
9
Q
How can a standard solution be prepared?
A
- weighing a primary standard accurately
- dissolving in a small volume of solvent (usually deionised or distilled water) in a beaker
- Transferring the solution and risings into a volumetric flask
- making up to the graduation mark with solvent
- stoppering and inverting
10
Q
What is another method of making a standard solution?
A
- 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
