Chemistry (Year 12) - Volumetric Analysis
Importance of Rinsing
Each piece of glassware should be rinsed before titration. Rinsing glassware before titration ensures the equipment is clean and free of any leftover substances. This is important because any extra chemicals could interfere with the results, leading to inaccurate measurements.
When rinsing, if the solution concentration needs to be kept the same, the glassware should be rinsed with the solution it will store.
If the number of moles needs to be kept the same, the glassware should be rinsed with deionised water.
The volumetric flask is used to prepare and store standard solutions. It will store more solution than required for a single titration, so multiple trials can be conducted.
Given that the number of moles of standard solutions must be held constant, the volumetric flask is rinsed with deionised water.
Pipettes are used to accurately measure and transfer solutions in 10 mL or 25 mL portions known as ‘aliquots’ between glassware.
The pipette is rinsed with the solution it is transferring. Rinsing with water would dilute the exact amount that is meant to be transferred (i.e. 10 mL or 25 mL), therefore affecting the concentration.
A burette is used to store the titre solution (usually the known or standard solution) and slowly transfer it to the conical flask, until the titration is complete.
The burette is rinsed with the titre solution. Rinsing with the water would dilute the exact amount of titre solution in the burette (i.e. 50 mL), therefore affecting the concentration.
A conical flask stores the analyte (usually the unknown solution) and indicator, and receives the titre solution. It is where the titration reaction takes place.
The conical flask is rinsed with deionised water. Rinsing it with water will dilute the concentration of the aliquot stored, but it won’t change the number of moles of analyte in the conical flask (which is what we are trying to hold constant), therefore it won’t affect the outcome of the titration.