question

significant figures

answer

the minimum number of digits needed to write a given value in scientific notation without any loss of accuracy

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interpolation

answer

estimate all readings to the nearest tenth of the distance between scale divisions

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significant figures in arithmetic

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in a series of calculations, carry the extra digits through to the final result then round.

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significant figures in rounding

answer

if the digit is to be removed and is less than 5, the preceding digit stays the same
if greater than 5, the preceding digit increases by 1
if equal to 5, preceding digit remains the same or increases by 1, whichever gives an even digit

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significant figures and addition and subtraction

answer

round according to the number with the most uncertainty, that is, the answer is limited by the least certain number

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significant figures and multiplication and division

answer

the answer is limited to the number of digits contained in the number with the fewest significant figures

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significant figures and logarithms and antilogarithms

answer

the number of digits in the mantissa of (log x) is the number of significant figures in x.

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characteristic

answer

the part of a logarithm to the left of the decimal point

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mantissa

answer

the part of a logarithm to the right of the decimal point

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significant figures in graphs

answer

depends on the purpose of the graph.
if to display qualitative behavior of data, then sig figs are irrelevant.
if to display precise values, then several sig figs

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systematic error
determinate error

answer

occurs in the same direction each time (high or low), often resulting from poor technique

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how to detect systematic error

answer

analyze samples of known composition, 'blank' samples containing none of the sought analyte; use different analytical methods to measure same quantity; Round Robin experiment

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Round Robin experiment

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assign different people/labs to analyze identical samples

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random error
indeterminate error

answer

measurement has an equal probability of being high or low; obeys laws of statistics

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accuracy

answer

agreement of a particular value with the "true" value.

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precision

answer

degree of agreement among several elements of the same quantity

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absolute uncertainty

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expression of the margin of uncertainty associated with a measurement

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relative uncertainty

answer

compares the size of the absolute uncertainty with the size of its associated measurement

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percent relative uncertainty

answer

100 * relative uncertainty

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propagation of uncertainty from random error
addition and subtraction

answer

if A=B+-C+-D
Ua=(Ub^2+Uc^2+Ud^2)^1/2
abs uncertainty used

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propagation of uncertainty from random error
multiplication and division

answer

A=B*/C*/D
%RUa=[(%RUb)^2+(%RUc)^2+(%RUd)^2]^1/2
percent relative uncertainty used

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propagation of uncertainty
mixed operations

answer

same manner as the calculations are performed

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real rule of significant figures

answer

THe first uncertain figure is the last significant figure

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propagation of uncertainty
exponents

answer

%RUy=a(%RUx)

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propagation of uncertainty
logarithms

answer

Uy=(1/ln10)*RUx

question

propagation of uncertainty
natural log

answer

Uy=RUx

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propagation of uncertainty
power of 10

answer

RUy=(ln10)Ux

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propagation of uncertainty
base e

answer

RUy=Ux

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uncertainty in molecular masses

answer

Use rule for addition and subtraction, then multiply by n moles per identical atom

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Gaussian distribution

answer

Theoretical bell-shaped distribution of measurements when all error is random. The center of the curve is the mean, and the width is characterized by the standard deviation.

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mean

answer

average

[image]

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standard deviation

answer

measure of how closely the data are clustered to the mean.

[image]

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degrees of freedom

answer

the number of independent measurements

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variance

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standard deviation squared

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relative standard deviation

answer

100 * std. dev./ mean

question

significant figures in mean and standard deviation

answer

where uncertainty begins according to std. dev., that's where significant figures are.

question

formula for Gaussian curve

answer

[image]

question

Z

answer

[image]

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confidence interval

answer

[image]

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Student's t

answer

statistical tool used to express confidence intervals and to compare results from different experiments.

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Student's t test

answer

used to compare one set of data with another to decide whether or not they are "the same"

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null hypothesis

answer

the two sets of data are the same

question

alternate hypothesis

answer

the two sets of data are different

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when to use Student's t test

answer

comparing a measured result with a known value, replicate measurements, individual differences

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t calc equation known value

answer

[image]

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t calc equation replicate measurements if std. devs. equal

answer

[image]

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s pooled replicate measurements

answer

[image]

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t calc equation replicate measurements if std. devs. inequal

answer

[image]

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F test

answer

compares standard deviations

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F calc

answer

[image]

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Grubbs test

answer

determines whether one measurement can be thrown away -- whether it is an outlier or not

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G calc

answer

[image]

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Real rule for bad data

answer

Dropped sample? Pretty obvious
Be hesitant if not certain
Grubbs test is not very reliable

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Calibration curve

answer

a graph showing the value of some property versus concentration of analyte. When the same property of an unknown is measured, its concentration can be determined from the graph.

[image]

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method of least squares

answer

process of fitting a mathematical function to a set of measured points by minimizing the sum of the squares of the distances from the points to the curve.

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standard solutions

answer

a solution whose composition is known by virtue of the way it was made from a reagent of known purity or by virtue of its reaction with a known quantity of standard reagent

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blank solution

answer

a solution that does not contain analyte; used to correct for interferences

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linear range

answer

the analyte concentration range over which response is proportional to concentration

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dynamic range

answer

the analyte concentration range over which there is a measurable response to analyte.

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quality assurance

answer

Quantitative indications that indicate whether data requirements have been met.

Also refers to the broader process that includes quality control, quality assessment, and documentation of procedures and results designed to ensure adequate data quality.

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Use objective

answer

states the purpose for which results will be used

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specifications

answer

describes how good analytical results need to be and what precautions are required in an analytical method.

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false positive

answer

a conclusion that the concentration of analyte exceeds a certain limit when, in fact, the concentration is below the limit

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false negative

answer

a conclusion that the concentration of analyte is below a certain limit when, in fact, the concentration is above the liimit.

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selectivity

answer

being able to distinguish analyte from other species in the the sample

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sensitivity

answer

the capability of responding reliably and measurably to changes in analyte concentration.

Slope of the calibration curve

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method blank

answer

a sample containing all components except analyte and is taken through all steps of the analytical process.

Response is subtracted from sample's response.

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reagent blank

answer

a solution prepared from all of the reagents, but no analyte; for measuring response of analytical method to impurities in reagents and other effects caused by anything but the analyte

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field blank

answer

a blank sample exposed to the environment at the sample collection site and transported in the same manner as other samples between the lab and the field.

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matrix

answer

everything in the sample other than analyte

Also, the virtual reality which the machines have set us in while they harvest our bodies for energy. Ignore that it would be incredibly inefficient.

question

spike

answer

addition of a known compound (with known concentration) to an unknown

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spike recovery

answer

[image]

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calibration check

answer

the analysis of a solution formulated by the analyst to contain a known concentration of analyte

Ensures that procedures and instruments are functioning correctly.

question

performance test samples

answer

inserted in a series of measurements to see if a procedures gives correct results when the analyst does not know the right answer

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standard operating procedures

answer

a written procedure that must be rigorously follow to ensure the quality of a chemical analysis

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control chart

answer

a visual representation of a confidence interval for a Gaussian distribution

question

assessment

answer

the process of collecting data to show that analytical procedures operating within specified limits and verifying that final results meet use objectives

question

method validation

answer

the process of proving that an analytical process is acceptable for its intended purpose

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specificity

answer

the ability of an analytical method to distinguish the analyte from everything else that might be in the sample

question

linearity

answer

measures how well a calibration curve follows a straight line

question

square of the correlation coefficient

answer

measure of goodness of fit of data points to a straight line.

Closer to 1 = better

question

how to demonstrate accuracy

answer

Analyze a standard reference material
compare results of different methods
spike a blank sample with analyte
standard additions

question

reproducibility of results

answer

precision

(alternate definition)

question

range

answer

concentration interval over which linearity, accuracy, and precision are all acceptable

question

detection limit

answer

the smallest quantity of analyte that is "significantly different" from the blank.

*
*

question

procedure for detection limit determination

answer

[image]

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quantitation limit

answer

[image]

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reporting limit

answer

the concentration below which regulatory rules say that a given analyte is reported as "not detected"

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robustness

answer

the ability of an analytical method to be unaffected by small, deliberate changes in operating parameters

question

standard addition

answer

known quantities of analyte are added to the unknown and the responses are recorded. This keeps any matrix effect constant.

question

matrix effect

answer

a change in the analytical signal caused by anything in the sample other than the analyte

question

standard addition equations

answer

[image]

question

standard addition with constant total volume

answer

[image]

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standard addition with varying total volume

answer

[image]

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internal standard

answer

a known amount of a compound, different from analyte, that is added to the unknown. Signal from the analyte is compared with signal from the internal standard to find out how much analyte is present.

question

response factor, F

answer

[image]

Test #2 – Quantitative Analysis – Flashcards

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