CHEM 211 Final Exam Questions With
Complete Answers
What is an assay? - ANSWER The process of determining the amount of an
analyte in a sample
What is an analyte? - ANSWER The chemical substance being measured
What is qualitative analysis? - ANSWER Identification of the elements, ions or
compounds that are present in an unknown sample
What is quantitative analysis? - ANSWER Concerned with the determination of
the quantity of one or more components of the sample
What are the advantages of visual detection? - ANSWER Simple, low-cost, and
no maintenance
What are the disadvantages of visual detection? - ANSWER Subjectivity, time
consuming, may not be very sensitive
What is a signal? - ANSWER A measured quantity that is correlated to the
amount of analyte
What is a noise? - ANSWER Unwanted variation in a measured quantity that
takes form of random fluctuations
What is the signal-to-noise ratio? - ANSWER The magnitude of the signal divided
by the magnitude of the noise
What S/N is required to resolve an analytical signal? - ANSWER S/N > 3
What is the background of a detection limit? - ANSWER Approximately constant
signal that is measured in the absence of the analyte
What is the detection limit? - ANSWER The amount of analyte that corresponds
to a signal just greater than the means of the background plus three standard
deviations of the noise
What is the equation for the detection limit? - ANSWER Signal > Mean
Background + 3SD background
What is S/N proportional to? - ANSWER Sqrt of the number of trials
,What is a sample matrix? - ANSWER All of the components of the sample except
the analyte
What is a blank? - ANSWER A man made sample matrix which lacks the analyte
What is a positive control? - ANSWER A standard sample that contains the
analyte of interest that helps prevent false negative results
What is a negative control? - ANSWER A standard sample that does not contain
any analyte to help prevent false positives
What is interference? - ANSWER A specific chemical substance in the matrix
that causes an error in the measurement
What is a masking agent? - ANSWER A reagent that prevents one or more
components in a sample from interfering with an analysis
What is selectivity? - ANSWER The extent to which other substances interfere
with the determination of an analyte
How can interferences impact measurments? - ANSWER Act on the analyte
Act on the reagent
Cause a background signal
What is accuracy? - ANSWER Accuracy is how close an experimental value is to
the true value
What is precision? - ANSWER Precision is how close a set of measurements are
to each other (SD)
What is absolute error? - ANSWER The difference between the measured and
true value
E = Xmeas - Xtrue
What is relative error? - ANSWER Error in measurement expressed as a
percentage
E = (Xmeas-Xtru)/Xtru x100
What are replicates? - ANSWER Samples from the same source run using the
same method under the same conditions
, What is random error? - ANSWER Error that can be treated with statistics
Symmetric about the true value
Looks like a random scattering around the mean
What is a systematic error? - ANSWER An error that introduces bias (always
higher or lower) introducing a bias
What are the three types of systematic error? - ANSWER Instrument, Method
and Personal
Describe instrument errors? - ANSWER Voltage drift which can be corrected
with calibration
Describe some method errors? - ANSWER Chemistry does not behave as
expected, such as an incomplete reactions or interference from non-analytes
What are personal errors? - ANSWER Incorrect recording of the data or from
deviations from an established method
What is a proportional error? - ANSWER An error that is always a specific %
higher or lower than the measurement
What is a constant error? - ANSWER An error that measures a constant value
lower or higher than the true value
What are the three standard deviations (1, 2, 3) - ANSWER 68, 95, 99.7 rule
What is relative standard deviation? - ANSWER S/Mean * 100%
How can error be propagated during addition and subtraction? - ANSWER
Sqrt(S1^2+S2^2)
What is the equation for a confidence interval with a T statistic? - ANSWER u = x
+- ts/sqrtN
U = population mean
x = sample mean
t = t-statistic
s = sample standard deviation
N = number of measures
When is the case one T test used? - ANSWER case one T test is used when you
want to compare an experimental value to a known value
Complete Answers
What is an assay? - ANSWER The process of determining the amount of an
analyte in a sample
What is an analyte? - ANSWER The chemical substance being measured
What is qualitative analysis? - ANSWER Identification of the elements, ions or
compounds that are present in an unknown sample
What is quantitative analysis? - ANSWER Concerned with the determination of
the quantity of one or more components of the sample
What are the advantages of visual detection? - ANSWER Simple, low-cost, and
no maintenance
What are the disadvantages of visual detection? - ANSWER Subjectivity, time
consuming, may not be very sensitive
What is a signal? - ANSWER A measured quantity that is correlated to the
amount of analyte
What is a noise? - ANSWER Unwanted variation in a measured quantity that
takes form of random fluctuations
What is the signal-to-noise ratio? - ANSWER The magnitude of the signal divided
by the magnitude of the noise
What S/N is required to resolve an analytical signal? - ANSWER S/N > 3
What is the background of a detection limit? - ANSWER Approximately constant
signal that is measured in the absence of the analyte
What is the detection limit? - ANSWER The amount of analyte that corresponds
to a signal just greater than the means of the background plus three standard
deviations of the noise
What is the equation for the detection limit? - ANSWER Signal > Mean
Background + 3SD background
What is S/N proportional to? - ANSWER Sqrt of the number of trials
,What is a sample matrix? - ANSWER All of the components of the sample except
the analyte
What is a blank? - ANSWER A man made sample matrix which lacks the analyte
What is a positive control? - ANSWER A standard sample that contains the
analyte of interest that helps prevent false negative results
What is a negative control? - ANSWER A standard sample that does not contain
any analyte to help prevent false positives
What is interference? - ANSWER A specific chemical substance in the matrix
that causes an error in the measurement
What is a masking agent? - ANSWER A reagent that prevents one or more
components in a sample from interfering with an analysis
What is selectivity? - ANSWER The extent to which other substances interfere
with the determination of an analyte
How can interferences impact measurments? - ANSWER Act on the analyte
Act on the reagent
Cause a background signal
What is accuracy? - ANSWER Accuracy is how close an experimental value is to
the true value
What is precision? - ANSWER Precision is how close a set of measurements are
to each other (SD)
What is absolute error? - ANSWER The difference between the measured and
true value
E = Xmeas - Xtrue
What is relative error? - ANSWER Error in measurement expressed as a
percentage
E = (Xmeas-Xtru)/Xtru x100
What are replicates? - ANSWER Samples from the same source run using the
same method under the same conditions
, What is random error? - ANSWER Error that can be treated with statistics
Symmetric about the true value
Looks like a random scattering around the mean
What is a systematic error? - ANSWER An error that introduces bias (always
higher or lower) introducing a bias
What are the three types of systematic error? - ANSWER Instrument, Method
and Personal
Describe instrument errors? - ANSWER Voltage drift which can be corrected
with calibration
Describe some method errors? - ANSWER Chemistry does not behave as
expected, such as an incomplete reactions or interference from non-analytes
What are personal errors? - ANSWER Incorrect recording of the data or from
deviations from an established method
What is a proportional error? - ANSWER An error that is always a specific %
higher or lower than the measurement
What is a constant error? - ANSWER An error that measures a constant value
lower or higher than the true value
What are the three standard deviations (1, 2, 3) - ANSWER 68, 95, 99.7 rule
What is relative standard deviation? - ANSWER S/Mean * 100%
How can error be propagated during addition and subtraction? - ANSWER
Sqrt(S1^2+S2^2)
What is the equation for a confidence interval with a T statistic? - ANSWER u = x
+- ts/sqrtN
U = population mean
x = sample mean
t = t-statistic
s = sample standard deviation
N = number of measures
When is the case one T test used? - ANSWER case one T test is used when you
want to compare an experimental value to a known value
