Question

1. What are the three most common types of determinate errors? Give at least 2 exampies for each type

Answer 1

Determinate or systematic errors are those errors which can be avoided or whose magnitude can be determined in experiment. These errors are determinable and presumably can be either avoided or corrected. Systemic errors are classified into 4 categories as :

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

Operational and personal error :
Personal errors are errors for which the individual person who is doing/conducting the experiment is responsible and are not connected with the method or procedure. example : unable to judge color change

When errors occur during operation of experiment, these are called as operational error example : 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 correct operational techniques is not followed

Instrumental and Reagent errors :
These are errors which occur due to faulty instrument or reagent containing impurities example : use of un-calibrated weights, un-calibrated burette, pipette and measuring flasks in experiment.

Errors of Method :
This type of error occurs due to method employed in experiment and is difficult to correct.

Example : in gravimetric analysis, error occurs due to Insolubility of precipitates, co-precipitates, post-precipitates, decomposition, and volatilization.

In titration analysis, errors occur due to failure of reaction, side reaction or 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 example : 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.