erros, random errors and statical data in chemical analyses

Question 1

it is impossible that the analytical results are free of ___ or ___

Answer 1

errors
uncertainties

Question 2

statical calculations for use to judge the ____ of experimental measurements

Answer 2

quality

Question 3

measurements are always accompanied by _____. the _____ always fall within a range due to uncertainty.

Answer 3

uncertainty
true value

Question 4

true or false:
data of unknown quality are worthless

Answer 4

true

Question 5

true or false:
the true value of a measurement is always known exactly

Answer 5

false - never known exactly

Question 6

how to enhance the quality of data

Answer 6

calibrating equipment

Question 7

what is the question to answer before beginning an analysis

Answer 7

what is the max. error that i can tolerate in the result?

Question 8

it measures the location of the middle of a distribution

Answer 8

mean
median

Question 9

it is used when 2 or more measurements is their average value

Answer 9

mean

Question 10

it is used advantageously when a set of data contains an outlier (result v different from the data), a result that differs significantly from others in set

Answer 10

median

Question 11

it describes the reproducibility of measurements: the closeness of results to each other

Answer 11

precision

Question 12

precision is determined by repeating the measurements on _____

Answer 12

replicate samples

Question 13

what are the 3 terms to describe the precision of a set of replicate data

Answer 13

standard deviation (most commonly used)
variance
coefficient of variation

Question 14

it indicates the closeness of the measurements to its true or accepted value and is expressed by the error

Answer 14

accuracy

Question 15

to determine accuracy, we have to know the ___ and this value is exactly what we are seeking in the analysis

Answer 15

true value

Question 16

true or false:
results cannot be precise without being accurate and accurate without being precise

Answer 16

false - results can be precise without being accurate and accurate without being precise

Question 17

what are the 2 types of error

Answer 17

random error - indeterminate
systematic error - determinate

Question 18

this type of error causes data to be more scattered more or less symmetrically around a mean value

Answer 18

random error

Question 19

this type of error causes the mean of set data to differ from the accepted value

Answer 19

systematic error

Question 20

what do these error affect
random error -
systematic error -

Answer 20

random error - the precision of measurement
systematic error - the accuracy of results

Question 21

this error usually occur occasionally. they are oftem large and may cause a result to be either high or low

Answer 21

gross error

Question 22

gross errors lead to ____, result that appear to differ markedly from all other data in a set of replicate measurements

Answer 22

outliers

Question 23

what are the 3 types of systematic error

Answer 23

instrument errors
method errors
personal errors

Question 24

which type of systematic error is difficult to deal with

Answer 24

method errors

Question 25

systematic instrument errors are usually corrected by _______

Answer 25

periodic calibration of equipment

Question 26

most personal errors can be minimized by ____ and ____

Answer 26

care and self discipline

Question 27

____ is an analytical method is particularly difficult to detect

Answer 27

bias

Question 28

what is the best way to estimate the bias of an analytical method

Answer 28

SRMs - standard reference materials

Question 29

examples of SRMs

Answer 29

inorganics in marine sediment
913a uric acid clinical standard
84L or 185h potassium hydrogen phthalate
1577c bovine liver

Question 30

in detecting systematic methods error, if SRMs are not available, use ____

Answer 30

second independent and reliable analytical method

Question 31

in detecting systematic method errors, blank determinations reveal ____ and ____ data

Answer 31

errors
correct

Question 32

constant errors can be detected using _____ and ____

Answer 32

blank determinants
varying the sample size

Question 33

true or false:
all measurements contain random errors

Answer 33

true

Question 34

true or false:
the nature of random errors are not accumulative

Answer 34

false - they are accumulative

Question 35

do not confuse the ______ sample with the ______ sample

Answer 35

statistical
analytical

Question 36

what is one of the best ways of indicating reliability to give a ____ at the ____ or ____ confidence level

Answer 36

confidence interval
90%
95%

Question 37

define a numerical interval around that conatins with a certain probability

Answer 37

confidence limits

Question 38

it is the numerical magnitude of the confidence limit

Answer 38

confidence limit

Question 39

the use of confidence limit is valid ONLY when ______ are absent

Answer 39

determinate errors (systematic error)

Question 40

a plot of instrument response versus known analyte concentrations is used to produce a ______

Answer 40

calibration curve

Question 41

what are some sources of random uncertainties in the calibration of pipet

Answer 41

1. visual judgements (lvl of water w respect to the marking on the pipet)
2. variation in the drainage time and the angle
3. temp fluctuations which affect the vol. of the pipet
4. variations and drafts that cause small variations in the balance reading

Question 42

population mean symbol

Answer 42

μ

Question 43

sample mean symbol

Answer 43

X̄