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PRELIMS > CHEM: Errors in Chemical Analysis > Flashcards

CHEM: Errors in Chemical Analysis Flashcards

1
Q

(TRUE OR FALSE)
Data of unknown quality are useless!

A

true

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2
Q

(true or false)
All laboratory measurements contain
experimental error.

A

true

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3
Q

true or false

It is necessary to determine the magnitude of the accuracy and reliability in your measurements.

A

true

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4
Q

true or false

No measurement is perfectly accurate or exact. Many instrumental, physical and human limitations cause measurements to deviate from the “true” values of the quantities being measured. These deviations are called “experimental uncertainties,” but more commonly the shorter word “error” is used.

A

true

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5
Q

two or more determinations on the same sample
Example: One student measures Fe (III) concentrations six times.

A

Replicates

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6
Q

average or arithmetic mean

A

Mean

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7
Q

the middle value of replicate data

A

median

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8
Q

(true or false)

If an odd number of replicates, the middle value of replicate data

A

true

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9
Q

(true or false)

If an even number of replicates, the middle two values are averaged to obtain the median

A

true

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10
Q

describes the reproducibility of measurements.

A

Precision

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11
Q

How close are results which have been obtained in exactly the same way?

A

Precision

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12
Q

derived from the deviation from the Mean

A

reproducibility

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13
Q

of an element of a data set is the absolute difference between that element and a given point. Typically the point from which the deviation is measured is the value of either the median or the mean of the data set

A

absolute deviation (D)

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14
Q

is the average of the absolute deviations and is a summary statistic of statistical dispersion or variability.

A

Average absolute deviation or Average deviation or mean absolute deviation

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15
Q

Average absolute deviation or Average deviation or mean absolute deviation

A

Standard Deviation

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16
Q

is a measure of the dispersion of a collection of number

A

Standard Deviation

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17
Q

measures the spread of the data about the mean value. It is useful in comparing sets of data which may have the same mean but a different range

A

Standard Deviation

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18
Q

is a measure of statistical dispersion

A

Variance

19
Q

is the average squared deviations about the mean. Thus, variance is the square of the standard deviation.

A

variance

20
Q

is a normalized measure of dispersion of a probability distribution. It is defined as the ratio of the standard deviation to the mean

A

Coefficient of Variation (CV)

21
Q

the closeness of the measurement to the true or accepted value

A

Accuracy

22
Q

called as the error:
absolute or relative error of a result to its true value.

A

closeness

23
Q

Occasional error that obviously differs significantly from the rest of the results

A

Outlier

24
Q

Described by the standard deviation, the variance and the
coefficient of variation (all are function of the deviation from the mean).

A

•Precision

25
Q

Described by the absolute and relative error.

A

Accuracy

26
Q

the difference between the experimental value and the true value. Has a sign and experimental units

A

Absolute Error (E)

27
Q

the absolute error corrected for the size of the measurement or expressed as the fraction, %, or parts-per-thousand (ppt) of the true value. Er has a sign, but no units.

A

Relative Error (Er)

28
Q

true or false

Systematic or determinate errors affect accuracy

A

true

29
Q

( true or false)
Random or indeterminate errors affect precision!

A

true

30
Q

(true or false)
Gross errors or blunders lead to outlier’s and require statistical techniques to be rejected.

A

true

31
Q

failure to calibrate, degradation of parts in the instrument, power fluctuations, etc

A

Instrument errors

32
Q

errors due to no ideal physical or chemical behavior - completeness and speed of reaction, interfering side reactions, sampling problems

A

Method errors

33
Q

occur where measurements require judgment, result from prejudice, color acuity problems

A

Personal errors

34
Q

Potential Instrument Errors

A

Variation in temperature
•Contamination of the equipment
•Power fluctuations
•Component failure
All of these can be corrected by calibration or proper instrumentation maintenance.

35
Q

method errors

A

Slow or incomplete reactions
•Unstable species
•Nonspecific reagents
•Side reactions
These can be corrected with proper method development

36
Q

Personal Errors

A

Misreading of data
•Improper calibration
•Poor technique/sample preparation
•Personal bias
•Improper calculation of results
These are blunders that can be minimized or eliminated with proper training and experience

37
Q

Es is of the same magnitude, regardless of the size of the measurement.
•This error can be minimized when larger samples are used. In other words, the relative error decreases with increasing amount of analyte.

A

Constant errors

38
Q

Es increases or decreases with increasing or decreasing sample size, respectively. In other words, the relative error remains constant.

A

Proportional errors

39
Q

true or false

  1. Analysis of standard samples
    •2. Independent Analysis: Analysis using a “Reference Method” or “Reference Lab”
    •3. Blank determinations
    •4. Variation in sample size: detects constant error only
A

true

40
Q

true or false

caused by uncontrollable variables which normally cannot be defined
•The accumulated effect causes replicate measurements to fluctuate randomly around the mean.
• Random errors give rise to a normal or Gaussian curve.
• Results can be evaluated using statistics
• Usually statistical analysis assumes a normal distribution

A

true

41
Q

named after Carl Friedrich Gauss
•characteristic symmetric “bell shape curve” that quickly falls off towards plus/minus infinity

A

Normal or Gaussian Curve

42
Q

(true or false)
gross errors cause an experimental value to be discarded.
• Lead to outlier’s and require statistical techniques to be rejected.

A

true

43
Q

Examples of _________ are an obviously “overrun end point“ (titration), instrument breakdown, loss of a crucial sample, and
discovery that a “pure” reagent was actually contaminated.

A

gross error

44
Q

true or false

We do NOT use data obtained when gross error has occurred during collection.

A

true

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