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Classification of Errors

Classification of Errors:
Errors are classified in two types – Systemic (Determinate) and Random (Indeterminate) errors

Systemic (Determinate) errors:
Errors which can be avoided or whose magnitude can be determined is called as systemic errors. It can be determinable and presumably can be either avoided or corrected. Systemic errors further classified as

  • Operational and personal error
  • Instrumental error
  • Errors of method
  • Additive or proportional error

Operational and personal error:
Errors for which the individual analyst is responsible and are not connected with the method or procedure is called as personal errors e.g. unable to judge color change

When errors occur during operation is called as operational error e.g. transfers of solution, effervescence, incomplete drying, underweighting of precipitates, overweighing of precipitates, and insufficient cooling of precipitates. These errors are physical in nature and occur when sound analytical techniques is not followed


Instrumental and Reagent errors:
Errors occur due to faulty instrument or reagent containing impurities e.g. un-calibrated weights, un-calibrated burette, pipette and measuring flasks.

Errors of Method:
When errors occur due to method, it is difficult to correct. In gravimetric analysis, error occurs due to Insolubility of precipitates, co-precipitates, post-precipitates, decomposition, and volatilization.

In titrimetric analysis errors occur due to failure of reaction, side reaction, reaction of substance other than the constituent being determined, difference between observed end point and the stoichiometric equivalence point of a reaction.


Additive or proportional errors:
Additive error does not depend on constituent present in the determination e.g. loss in weight of a crucible in which a precipitate is ignited.

Proportional error depends on the amount of the constituent e.g. impurities in standard compound.

Random Errors:
It occurs accidentally or randomly so called as indeterminate or accidental or random error. Analyst has no control in this error. It follows a random distribution and a mathematical law of probability can be applied.

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