Why, when I perform an equivalence point titration using an automatic titrator, do I get a different result as to when I titrate manually using a color indicator?
This discrepancy in results is primarily noticeable when performing acid/base titrations using one of the pH indicators. The first reason for this is that these pH indicators change color over a pH range rather than at a fixed value. The actual point at which the color change occurs is very much sample dependant and may not coincide with the chemical equivalence point. This can result in a small discrepancy in result which is easily nullified by standardizing the titrant using a similar method as is used for samples. The second reason for this difference is primarily one of the sensitivity of the human eye to color change. While a color change may have already started to occur, the human eye has still not detected any change. This can be demonstrated by using a photometric sensor such as the METTLER TOLEDO DP5 phototrodes. Using one of these sensors there is a clear change in light transmittance long before the human eye detects any color change.
This discrepancy in results is primarily noticeable when performing acid/base titrations using one of the pH indicators. The first reason for this is that these pH indicators change color over a pH range rather than at a fixed value. The actual point at which the color change occurs is very much sample dependant and may not coincide with the chemical equivalence point. This can result in a small discrepancy in result which is easily nullified by standardizing the titrant using a similar method as is used for samples. The second reason for this difference is primarily one of the sensitivity of the human eye to color change. While a color change may have already started to occur, the human eye has still not detected any change. This can be demonstrated by using a photometric sensor such as the METTLER TOLEDO DP5 phototrodes. Using one of these sensors there is a clear change in light transmittance long before the human eye detects any color change. In the typical acid/base titration usin
Related Questions
- Why, when I perform an equivalence point titration using an automatic titrator, do I get a different result as to when I titrate manually using a color indicator?
- How does knowing the equivalence point in an acid-base titration help you choose an indicator for titration?
- Why isn the equivalence point of acid-base titration always at pH7?
