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Accuracy and Precision

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okay let us start

the other areas of analytical chemistry

analytical chemistry qualitative

analysis

quantitative

what is the difference between accuracy

and precisions

value the average of the best

results obtained by efficient and

experienced workers

in many laboratories using

different techniques or those obtained

by using the most

highly sophisticated instruments is the

most

probable value generally taken as the

true value above

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between the result observed value

and the true value or most probable

value

precision and angular concordance of a

series of measurements of the

same quantity

law it represents how close the

measurements are to

each other

for example

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it

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the difference between the true value

and the measured value of

a quantity is known as error and either

numbers

in the value and that is

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accuracy

first one absolute error second one

relative error

it is the difference between the

observed value and the

true value that is absolute error

is x observed minus x

t where x obs

meaning observed value and x

t means true value

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next one is relative error it is the

ratio of the error to the

true or most probable value

it is usually represented

x observed minus x t divided by

x t into hundred percentage

the percentage then

parts per thousand dollar er

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operational and personal error then

method error instrumental and reagent

error

fourth one additive and proportional

error

indeterminate errors classifies

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can be avoided or its magnitude can be

determined these errors can either be

eliminated or improved by repetition

determination first of all not in the

operational error

another one misinterpreting directions

with respect to conditions such as

temperature ph

experiment conditions temperature ph

conditions now other misinterpreted

next one is instrumental and reagent

errors

it is due to the use of defective

instruments

or by using defective apparatus such as

balance weight glassware etc

the instrumental error is so useful

for the number

properly in accordance with the

requirement or one which attacks

glass

uh

such errors may arise from incorrect

sampling

incompleteness of reactions

so

analysis it arises due to side reactions

non-stoichiometry of the reaction etc

either number of volumetric analysis s

uh

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are independent of the amount of

constituent present

in determination

an example on a in weight of a crucible

in which precipitate is ignited or due

to errors

in weight etc

analysis precipitate crucible vegetable

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error depends upon the amount of

constituent present in

determinations example

presence of impurity in standard

substance

weight and hence the molarity of

solution prepared

either number one substance usage

solution preparing

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whose magnitude cannot be determined

these are a group of unsuspected and

non-reproducible errors otherwise

these errors are beyond the control of

analyst

either

due to the inability of the analyst to

distinguish between slightly different

readings colors position in needles etc

this cannot be corrected by a repetition

of the experiment because the inherent

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