Chapter 10: Summary

Question 1

all measurements contain __ and __

Answer 1

• errors
• uncertainties

Question 2

what is always provided

Answer 2

• estimate of quality
• reliability of collected data

Question 3

what is prepared to improve the reliability of results

Answer 3

two to five replicate samples

Question 4

what is used as a measure of central value of data

Answer 4

• mean or
• median

Question 5

what is measured to demonstrate reproducibility of data

Answer 5

precision

Question 6

why is it often more difficult to determine the accuracy of results than the precision

Answer 6

because true value is seldom known

Question 7

precise measurements are not __ all of the time

Answer 7

accurate

Question 8

arise from experimental variables that cannot be controlled or determined

Answer 8

Random or indeterminate errors

Question 9

Random error affect __

Answer 9

precision

Question 10

occur when instruments or measuring devices are uncalibrated or are calibrated improperly

Answer 10

Systematic or determinate errors

Question 11

caused by nonideal instrument behavior, by faulty calibrations, or by use under inappropriate conditions

Answer 11

instrumental errors

Question 12

arise from nonideal chemical or physical behavior of analytical systems

Answer 12

method errors

Question 13

result from carelessness, inattention, or personal limitations of the experimenter

Answer 13

personal errors

Question 14

are independent of the size of the sample being analyzed

Answer 14

constant errors

Question 15

decrease or increase in proportion to the size of the sample

Answer 15

proportional errors

Question 16

most personal errors can be minimized by what

Answer 16

• careful, disciplined laboratory work
• careful choice of methods and instruments

Question 17

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

Answer 17

analyzing standard reference materials (SRMs)

Question 18

contains the solvent and all the reagents in an analysis

Answer 18

blank

Question 19

blank that contain added constituents to simulate the __ __

Answer 19

sample matrix

Question 20

refers to the collection of all the constituents in the sample

Answer 20

matrix

Question 21

Random, or indeterminate, errors affect measuremetn __

Answer 21

precision

Question 22

where do random errors arise from

Answer 22

experimental variables that cannot be controlled or determined

Question 23

Example of random errors

Answer 23

1. random fluctuations in electrical noise
2. random inconsistencies in measurement readings
3. random changes in laboratory temperature

Question 24

systematic, or determinate, errors affect the __ of results

Answer 24

accuracy

Question 25

systematic errors often occur when?

Answer 25

instruments or measuring devices are uncalibrated or calibrated improperly

Question 26

systematic errors can be very __ and __ to detect

Answer 26

- subtle - difficult

Question 27

substance being determined

Answer 27

analyte

Question 28

occur infrequently and often result from an experimental blunder such as misreading a scale or interpreting a number incorrectly

Answer 28

gross errors

Question 29

occasional result in replicate measurements that differs significantly from the other results

Answer 29

outlier

Question 30

- measures the systematic error associated with an analysis - has negative sign if it causes the results to be low and positive sign otherwise

Answer 30

bias

Question 31

sign of bias if it causes results to be low

Answer 31

negative sign

Question 32

sign of bias if it causes results to be high

Answer 32

positive sign

Question 33

- determines the relationship between a measured quantity and the analyte concentration - very important part of any analytical procedure

Answer 33

calibration

Question 34

Of the three types of systematic errors encountered in a chemical analysis, what is usually the most difficult to identify and correct

Answer 34

method errors

Question 35

independent of the size of the sample being analyzed

Answer 35

constant errors

Question 36

decrease or increase in proportion to the size of the sample

Answer 36

proportional errors

Question 37

Equation for Mean

Answer 37

x̄ = sum of all measurements / no. of measurements

Question 38

Equation for Absolute Error

Answer 38

E = xi - xt

Question 39

Equation for Deviation from the mean

Answer 39

di = |xi - x̄ |

Question 40

Equation for Relative Error

Answer 40

Er = (xi - xt/ xt) x 100%