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Test #2 - Quantitative Analysis
Chapters 3, 4, 5.
96
Chemistry
Undergraduate 2
10/08/2012

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Term
significant figures
Definition
the minimum number of digits needed to write a given value in scientific notation without any loss of accuracy
Term
interpolation
Definition
estimate all readings to the nearest tenth of the distance between scale divisions
Term
significant figures in arithmetic
Definition
in a series of calculations, carry the extra digits through to the final result then round.
Term
significant figures in rounding
Definition
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
Term
significant figures and addition and subtraction
Definition
round according to the number with the most uncertainty, that is, the answer is limited by the least certain number
Term
significant figures and multiplication and division
Definition
the answer is limited to the number of digits contained in the number with the fewest significant figures
Term
significant figures and logarithms and antilogarithms
Definition
the number of digits in the mantissa of (log x) is the number of significant figures in x.
Term
characteristic
Definition
the part of a logarithm to the left of the decimal point
Term
mantissa
Definition
the part of a logarithm to the right of the decimal point
Term
significant figures in graphs
Definition
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
Term
systematic error
determinate error
Definition
occurs in the same direction each time (high or low), often resulting from poor technique
Term
how to detect systematic error
Definition
analyze samples of known composition, 'blank' samples containing none of the sought analyte; use different analytical methods to measure same quantity; Round Robin experiment
Term
Round Robin experiment
Definition
assign different people/labs to analyze identical samples
Term
random error
indeterminate error
Definition
measurement has an equal probability of being high or low; obeys laws of statistics
Term
accuracy
Definition
agreement of a particular value with the "true" value.
Term
precision
Definition
degree of agreement among several elements of the same quantity
Term
absolute uncertainty
Definition
expression of the margin of uncertainty associated with a measurement
Term
relative uncertainty
Definition
compares the size of the absolute uncertainty with the size of its associated measurement
Term
percent relative uncertainty
Definition
100 * relative uncertainty
Term
propagation of uncertainty from random error
addition and subtraction
Definition
if A=B+-C+-D
Ua=(Ub^2+Uc^2+Ud^2)^1/2
abs uncertainty used
Term
propagation of uncertainty from random error
multiplication and division
Definition
A=B*/C*/D
%RUa=[(%RUb)^2+(%RUc)^2+(%RUd)^2]^1/2
percent relative uncertainty used
Term
propagation of uncertainty
mixed operations
Definition
same manner as the calculations are performed
Term
real rule of significant figures
Definition
THe first uncertain figure is the last significant figure
Term
propagation of uncertainty
exponents
Definition
%RUy=a(%RUx)
Term
propagation of uncertainty
logarithms
Definition
Uy=(1/ln10)*RUx
Term
propagation of uncertainty
natural log
Definition
Uy=RUx
Term
propagation of uncertainty
power of 10
Definition
RUy=(ln10)Ux
Term
propagation of uncertainty
base e
Definition
RUy=Ux
Term
uncertainty in molecular masses
Definition
Use rule for addition and subtraction, then multiply by n moles per identical atom
Term
Gaussian distribution
Definition
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.
Term
mean
Definition

average

 

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Term
standard deviation
Definition

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

 

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Term
degrees of freedom
Definition
the number of independent measurements
Term
variance
Definition
standard deviation squared
Term
relative standard deviation
Definition
100 * std. dev./ mean
Term
significant figures in mean and standard deviation
Definition
where uncertainty begins according to std. dev., that's where significant figures are.
Term
formula for Gaussian curve
Definition
[image]
Term
Z
Definition
[image]
Term
confidence interval
Definition
[image]
Term
Student's t
Definition
statistical tool used to express confidence intervals and to compare results from different experiments.
Term
Student's t test
Definition
used to compare one set of data with another to decide whether or not they are "the same"
Term
null hypothesis
Definition
the two sets of data are the same
Term
alternate hypothesis
Definition
the two sets of data are different
Term
when to use Student's t test
Definition
comparing a measured result with a known value, replicate measurements, individual differences
Term
t calc equation known value
Definition
[image]
Term
t calc equation replicate measurements if std. devs. equal
Definition
[image]
Term
s pooled replicate measurements
Definition
[image]
Term
t calc equation replicate measurements if std. devs. inequal
Definition
[image]
Term
F test
Definition
compares standard deviations
Term
F calc
Definition
[image]
Term
Grubbs test
Definition
determines whether one measurement can be thrown away -- whether it is an outlier or not
Term
G calc
Definition
[image]
Term
Real rule for bad data
Definition
Dropped sample? Pretty obvious
Be hesitant if not certain
Grubbs test is not very reliable
Term
Calibration curve
Definition

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]

Term
method of least squares
Definition
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.
Term
standard solutions
Definition
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
Term
blank solution
Definition
a solution that does not contain analyte; used to correct for interferences
Term
linear range
Definition
the analyte concentration range over which response is proportional to concentration
Term
dynamic range
Definition
the analyte concentration range over which there is a measurable response to analyte.
Term
quality assurance
Definition
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.
Term
Use objective
Definition
states the purpose for which results will be used
Term
specifications
Definition
describes how good analytical results need to be and what precautions are required in an analytical method.
Term
false positive
Definition
a conclusion that the concentration of analyte exceeds a certain limit when, in fact, the concentration is below the limit
Term
false negative
Definition
a conclusion that the concentration of analyte is below a certain limit when, in fact, the concentration is above the liimit.
Term
selectivity
Definition
being able to distinguish analyte from other species in the the sample
Term
sensitivity
Definition
the capability of responding reliably and measurably to changes in analyte concentration.

Slope of the calibration curve
Term
method blank
Definition
a sample containing all components except analyte and is taken through all steps of the analytical process.

Response is subtracted from sample's response.
Term
reagent blank
Definition
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
Term
field blank
Definition
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.
Term
matrix
Definition
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.
Term
spike
Definition
addition of a known compound (with known concentration) to an unknown
Term
spike recovery
Definition
[image]
Term
calibration check
Definition
the analysis of a solution formulated by the analyst to contain a known concentration of analyte

Ensures that procedures and instruments are functioning correctly.
Term
performance test samples
Definition
inserted in a series of measurements to see if a procedures gives correct results when the analyst does not know the right answer
Term
standard operating procedures
Definition
a written procedure that must be rigorously follow to ensure the quality of a chemical analysis
Term
control chart
Definition
a visual representation of a confidence interval for a Gaussian distribution
Term
assessment
Definition
the process of collecting data to show that analytical procedures operating within specified limits and verifying that final results meet use objectives
Term
method validation
Definition
the process of proving that an analytical process is acceptable for its intended purpose
Term
specificity
Definition
the ability of an analytical method to distinguish the analyte from everything else that might be in the sample
Term
linearity
Definition
measures how well a calibration curve follows a straight line
Term
square of the correlation coefficient
Definition
measure of goodness of fit of data points to a straight line.

Closer to 1 = better
Term
how to demonstrate accuracy
Definition
Analyze a standard reference material
compare results of different methods
spike a blank sample with analyte
standard additions
Term
reproducibility of results
Definition
precision

(alternate definition)
Term
range
Definition
concentration interval over which linearity, accuracy, and precision are all acceptable
Term
detection limit
Definition
the smallest quantity of analyte that is "significantly different" from the blank.

*
*
Term
procedure for detection limit determination
Definition
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Term
quantitation limit
Definition
[image]
Term
reporting limit
Definition
the concentration below which regulatory rules say that a given analyte is reported as "not detected"
Term
robustness
Definition
the ability of an analytical method to be unaffected by small, deliberate changes in operating parameters
Term
standard addition
Definition
known quantities of analyte are added to the unknown and the responses are recorded. This keeps any matrix effect constant.
Term
matrix effect
Definition
a change in the analytical signal caused by anything in the sample other than the analyte
Term
standard addition equations
Definition
[image]
Term
standard addition with constant total volume
Definition
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Term
standard addition with varying total volume
Definition
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Term
internal standard
Definition
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.
Term
response factor, F
Definition
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