ERRORS IN ANALYSIS

Question 1

Analytical results are often used in the diagnosis of
disease, in the assessment of hazardous wastes and
pollution, in the solving of major crimes, and in the
quality control of industrial products. Errors in these
results can have serious personal and societal
effects.

Answer 1

ERRORS IN THE LABORATORY

Question 2

TYPES OF ERRORS

Answer 2

DETERMINATE OR SYSTEMATIC ERROR

Question 3

errors that can be determined or eliminated.
It affects the accuracy of results.

Answer 3

1. DETERMINATE OR SYSTEMATIC ERROR
2. INDETERMINATE OR RANDOM ERROR

Question 4

have a definite value, an
assignable cause, and are of the same
the magnitude for replicate measurements made in
the same way. They lead to bias in measurement
results.

Answer 4

Systematic errors

Question 4

have a definite value, an
assignable cause, and are of the same
the magnitude for replicate measurements made in
the same way. They lead to bias in measurement
results.

Answer 4

Systematic errors

Question 5

the deviation from the target value.
- measures the systematic error
associated with an analysis. It has a
negative sign if it causes the results to be
low and a positive sign

otherwise

Answer 5

Bias

Question 6

TYPES OF SYSTEMATIC ERRORS:

Answer 6

INSTRUMENTAL ERRORS, METHOD ERRORS, METHOD ERRORS

Question 7

errors that cannot be determined or
controlled. It affects precision.

Answer 7

INDETERMINATE OR RANDOM ERROR

Question 8

Random errors are the cumulative effect of
many small, uncontrollable variables and
personal judgments that lead to uncertainty in
a measured value.

Answer 8

INDETERMINATE OR RANDOM ERROR

Question 9

Presence of bubbles in one of the
trials, presence of bubbles in the reading in the
instruments, microclots in a plasma due to
particulate matter

Answer 9

INDETERMINATE OR RANDOM ERROR

Question 10

A volumetric flask or pipette was graduated
at 20oC and used at 25oC.

Answer 10

INSTRUMENTAL ERRORS

Question 11

In gravimetric method, if precipitate is not
sufficiently insoluble, a weight is less than the
correct one.

Answer 11

METHOD ERRORS

Question 12

Color blindness is a good example of a
limitation that could cause a personal error in a
volumetric analysis.

Answer 12

PERSONAL ERRORS

Question 13

EEFECTS OF SYSTEMATIC ERRORS:

Answer 13

CONSTANT ERRORS, PROPORTIONAL ERRORS,

Question 14

errors that are independent of the size of the
sample being analyzed.

Answer 14

CONSTANT ERRORS

Question 15

Here the value of absolute error is constant with
sample size, but the relative error varies when the
sample size is changed

Answer 15

CONSTANT ERRORS

Question 16

loss on the amount of precipitate due to large
amount of liquid.

Answer 16

CONSTANT ERRORS

Question 17

Presence of contaminants does not depend
on the size of the sample

Answer 17

PROPORTIONAL ERRORS

Question 18

• errors that decrease or increase in proportion to the
  size of the sample.

Answer 18

PROPORTIONAL ERRORS

Question 19

Here the value of absolute error varies with sample
size, but the relative error stays constant when the
sample size is changed.

Answer 19

PROPORTIONAL ERRORS

Question 20

It is impossible to have a perfect chemical analysis,
one that is free from errors and uncertainties

Answer 20

QUANTIFYING EXPERIMENTAL METHODS

Question 21

Does that mean your results are unreliable? So, what
do you do?

Answer 21

QUANTIFYING EXPERIMENTAL METHODS

Question 22

 Evaluate the error
- Where did it come from? How?
Perform same procedure from known values
 Compare from standard values
 Calibration of equipment
 Statistical treatments

Answer 22

BASIC STATISTICAL TREATMENT

Question 23

In order to improve the reliability and to obtain
information about the variability of results, two to five
portions (replicates) of a sample are usually carried
through an entire analytical procedure.

Answer 23

BASIC STATISTICAL TREATMENT

Question 24

________are samples of about the same size
that are carried through an analysis in exactly the
same way.

Answer 24

Replicates

Question 25

Individual results from a set of measurements are
seldom the same, so we usually consider the____________
estimate to be the central value for the set.

Answer 25

“best”