VOLUMETRIC ANALYSIS Flashcards
What is a solution of accurately known concentration called?
A standard solution
A standard solution is crucial for quantitative analysis in chemistry.
What are the steps to prepare a standard solution?
- Weigh a primary standard accurately
- Dissolve in a small volume of solvent (usually deionised or distilled water) in a beaker
- Transfer the solution and rinsings into a volumetric flask
- Make up to the graduation mark with solvent
- Stopper and invert
Each step ensures the accuracy of the solution’s concentration.
How can standard solutions be prepared by 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
This method is useful for creating solutions of lower concentrations.
What are the requirements for a primary standard?
- Must be available in a high state of purity
- Must be stable when solid and in solution
- Must be soluble
- Must have a reasonably high GFM
List examples of primary standards.
- Sodium carbonate, Na2CO3
- Hydrated oxalic acid, H2C2O4·2H2O
- Silver nitrate, AgNO3
- Potassium iodate, KIO3
- Potassium dichromate, K2Cr2O7
True or False: Sodium hydroxide is a primary standard.
False
Sodium hydroxide is not a primary standard due to its low GFM and instability.
Why must sodium hydroxide solution be standardized before use?
Because it has a relatively low GFM, is unstable as a solid (absorbs moisture), and unstable as a solution
What is the basis of complexometric titrations?
Reactions in which complexes are formed
What is EDTA used for in complexometric titrations?
To determine the concentration of metal ions in solution
What is a back titration?
A method to find the number of moles of a substance by reacting it with an excess volume of a reactant of known concentration
How is the number of moles of the reactant in excess determined in a back titration?
By titrating the resulting mixture
What can be calculated from the initial number of moles of a reactant in a back titration?
The number of moles used in the reaction and the initial number of moles of the substance being analyzed
When is a back titration particularly useful?
When trying to work out the quantity of a substance in a solid with a low solubility
