Volumetric Analysis Flashcards
What is a Volumetric Analysis?
Quantitative Technique
Involves measuring volume of a solution with a known concentration which is used to determine the concentration of the analyte.
What process is involved in a volumetric analysis?
Titration
Steps to a Volumetric Analysis
- Preparation of standard solution
- Titration between standard solution and solution to be standardised
- Titration between standardised solution and analyte
- Calculations to determine analyte concentration
Volumetric Flask
Used to prepare standard solution
A fixed volume usually 100mL or 250mL
Pipette
Used to transfer a known volume of solution being analyzed to the conical flask
Fixed volume, commonly 20 - 25mL
Aliquot
an amount taken from a larger quantity, so that it can be tested
Burette
A variable volume
Holds up to 50mL
Contains the standard solution
Titre
the volume of a solution required to complete a reaction in a titration.
Conical Flask
Used for holding the aliquot delivered by the pipette
What is a standard solution?
Concentration is accurately known, prepared in volumetric flask, prepared using a primary standard
Requirements of a primary standard
- available in pure form
- known formula
- stable enough to not react with the atmosphere
- soluble in water
- high molar mass
Standardization
A standard solution can be used to standardise another solution
Titration
adding one solution to another until a reaction is complete
Indicator
signals the point where neutralisation reaction is complete
Equivalence point
reaction is complete according to mole ratios in equation
Endpoint
when the indicator changes colour
Factors to consider when choosing an indicator
End point of the indicator must be close to the equivalence point of the reaction
What does CONCORDANT mean?
0.10mL between the lowest and highest titre
Why should we use concordant titres?
Increases reliability and precision of results, minimizing effects of random errors
STRONG ACIDS
HCl, NO3, H2SO4
WEAK ACIDS
Carboxylic acids
STRONG BASES
NaOH, KOH, Ba(OH)2
WEAK BASES
NH3
What are TITRATION CURVES?
Graph of Burette Volume versus pH in the titration flask
What are the types of experimental errors in a volumetric analysis?
- Rinsing Errors
- Indicator Errors
What are rinsing errors?
Lead to either overestimations or underestimations of analyte concentration
Effects size of the titre delivered
What should the volumetric flask be rinsed with?
Distilled Water
What should the pipette be rinsed with?
The solution it is to contain
Why shouldn’t we rinse the pipette with water?
- decrease the concentration of solution in the pipette
- hence a smaller titre of would be delivered by the burette to react completely
- leading to a lower calculated concentration (underestimation)
Why shouldn’t we rinse the pipette with a more concentrated solution?
- Increase the concentration of solution in the pipette
- Larger titre required to react completely
- Higher calculated concentration (overestimation)
What should the burette be rinsed with?
With the solution it is to contain
Why shouldn’t the burette be rinsed with water?
- dilute the concentration of solution in burette
- larger titre required to react completely
- higher calculated concentration of analyte
Why shouldn’t the burette be rinsed with a more concentrated solution?
- increase the concentration of solution in the burette
- smaller titre required to react completely
- lower calculated concentration of analyte
What should the conical flask be rinsed with?
Distilled water
Why shouldn’t you rinse the conical flask with the solution it is to contain?
- Increases the concentration of solution
- Greater titre required
- Overestimation
Poor Indicator Choice
Incorrect indicator choice can lead to overestimations and underestimations of final concentration
Missed Indicator Endpoint
If titration is stopped after endpoint, the size of the titre will be bigger than it should be
