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Sources of errors in titration


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Instant Notes in Analytical Chemistry Amazon

Instant Notes in Analytical Chemistry

by D. Kealey, P.J. Haines

Titration » Titration errors

There are several types of errors that can make titration result differ from the reality.

First, there is an intrinsic error of the method - end point is not identical with equivalence point and color changes of indicators are not instant. Reasons of this difference are discussed in details in the end point detection and acid-base titration end point detection sections.

In some cases excess of the titrant must be used as it is titrant color that signals end point. While this is also intrinsic characteristic of the method, it can be adjusted for by blind trials.

Then, there are errors that can be connected with volumetric glass accuracy. These can be adjusted for by careful calibration of the glassware. If for some reason calibration can't be done, we can minimalize errors using A class volumetric glass. We can also minimalize errors carefully selecting volumes of pipettes and burettes used. As it is discussed in the volumetric glassware and selection of sample size and titrant volume sections, using 50 mL burettes and about 80-90% of their volume guarantees the smallest possible relative error of titration (it doesn't guarantee accuracy of the determination). Also using large (20 or 25 mL) single volume pipettes means smaller relative errors.

Finally, there are thousands of possible random errors, that can't be adjusted for. Some of them are typical human errors, that can be limited by sticking to lab procedures, but as long as there is a human operator involved, they will be never completely eliminated. Some of possible cases are:

These are just examples. Every day in every lab in the world old mistakes are repeated and new cases are recorded.

Finally, each titration has its own quirks. They are usually related to chemical characteristics of titrant and other substances involved - NaOH used as a titrant tends to adsorb atmospheric CO2, KMnO4 and thiosulfate slowly decompose and so on. These will be addressed on individual titration procedure pages.

Page was last modified on May 25 2011, 23:46:54.

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