Reliability
The extent to which observations are consistent under identical circumstances
How is reliability achieved in titration?
A titration is repeated until at least three titres are obtained that are within narrowly specified limits (concordant titres)
How do concordant titres increase reliability?
Repeated measurement of the titres increases the reliability of the result and minimises errors that may have affected one titre more than others.
Accuracy
How close a measurement is to the true or accepted value (errors and limitations of instruments)
What are some errors made during titration that decrease accuracy?
- Misreading numbers on a scale- Using a pipette of incorrect volume- Spilling a portion of sample- Incorrect rinsing of volumetric glassware
Why should burettes and pipettes be rinsed with the acid or base they are to be filled with?
Rinsing with water only will dilute the acid or base solution
Why should conical flasks be rinsed only with water?
Rinsing with acidic or basic solutions will introduce unmeasured amounts of acids or bases into the flask, which can react and affect the results.- Only the number of moles present is important and adding water will not change the number of moles in the conical flask
What are some systematic errors that can occur during a titration?
- Uncertainty in volume measurements due to the limits of reading of equipment- Reading the scale on a burette with a constant parallax error
What is a random error that can occur during a titration?
- Uncertainty in pinpointing the exact colour change at the endpoint
Validity
The extent to which the process measured what was intended (do you address the question under investigation?)
How do you improve the validity of a titration?
- Choosing the right indicator so you are able to correctly determine the equivalence point.- Rinsing glassware with the right solution. If you don't, then you aren't testing what was intended to be tested as the concentration of the liquids will change.