First Exam Flashcards
This is the most common method for expressing the
concentration of a solution in biochemical studies.
Molarity
is one that contains a
precisely known concentration of solute.
Standard Solutions
is the one having
a concentration many folds higher than that actually required in
the experiment.
Stock Solutions
A solution which contains mole of the solute dissolved in 1 kg of
the solvent is called a molal solution.
Molality
expresses concentration in terms of the equivalents
of one chemical species reacting stoichiometrically with
another chemical species; a function of chemical reaction.
Normality
is the number of gram equivalents
of the solute per litre of the solution.
Normality
This is generally employed for those solutions in which a
substance is present in a very small quantity.
ppm or ppb
a measurement science consisting of a set of powerful ideas and
methods that are helpful in all fields of science and medicine
analytical chemistry
concerned with the chemical characterization of matter;
analytical chemistry
concerned with the theory and practice of methods used to
determine the composition of matter;
Analytical chemistry
involves separating, identifying and determining the relative
amounts of the components in a sample of matter.
analytical chemistry
is often called the central science
Chemistry
data based on numbers
quantitative data
data based on observations
qualitative data
• deals with the identification of elements, ions or compound present in a sample.
• concerned with what elements or compounds is in the sample.
• reveals the chemical identity of a species in the sample.
Qualitative analysis
• concerned with the determination of the amount of a particular substance present in a sample.
• establishes the relative amounts of one or more of these species or analytes.
Quantitative analysis
Examples of wet chemical methods
precipitation, extraction, distillation, boiling
or melting points, gravimetric and
titrimetric measurements.
Analytical measurements such as ——– are made using instrumentation
(conductivity, electrode potential, light absorption or
emission, mass-to-charge ratio,
fluorescence etc.)
the mass of the analyte or some compound chemically
related to it is determined.
gravimetric method
the volume of a solution containing sufficient reagent to
react completely with the analyte is measured.
volumetric method
employs instruments other than those used in
gravimetric and volumetric methods of analysis.
instrumental methods
involves the measurement of such electrical properties
as potential, current, resistance and quantity of electricity.
electroanalytical method
examples of electroanalytical method
Potentiometry
Voltammetry
Coulometry
based upon the measurement of the interactions between
electromagnetic radiation and the analyte atoms or molecules or
upon the production of such radiation by analytes.
spectroscopic method
examples of spectroscopic method
• UV-VIS Spectroscopy
• IR Spectroscopy
• Atomic Absorption Spectroscopy (AAS)
• Fluorescence Spectrophotometry
• NMR Spectroscopy
involves separation of sample components based on differences in their migration rates.
chromatographic method
examples of chromatographic method
• Thin Layer Chromatography (TLC)
• Gas Chromatography (GC)
• High Performance Liquid Chromatography (HPLC)
the classification of analyses are based on what 3?
Based on the extent of analysis
Based on the size of the sample available for
analysis
Based on the type of constituents
under the based on the extent of the analysis there are 3 types. what are they?
complete or exact
ultimate
proximate or partial
Steps in a Typical Quantitative Analysis
Selecting a Method of Analysis
Sampling
Preparing a Laboratory Sample
Defining Replicate Samples
Preparing Solutions of the Samples
Eliminating Interferences
Calibration and Measurement of Concentration
Calculating Results
Evaluating Results by Estimating their Reliability
what are the steps in an analytical process
sampling
sample preparation
chemical analysis
calibration curves
interpreting the results
The analysis is
meaningless unless:
⮚ you have collected the
sample properly;
⮚ you have taken measures
to ensure the reliability of
the analytical method;
⮚ you communicate your
results clearly and
completely.
The _______ is only the
middle portion of a process that
begins with a question and ends with
a conclusion.
chemical analysis
Chemists usually carry ________ replicates (portions) of a sample through an analytical procedure.
three to five
___________ are samples of about the same size that are carried through an analysis in exactly the same way.
Replicates
arithmetic mean or average
the quantity obtained by dividing the sum of replicate
measurements (xi) by the number of measurements (N) in the
set.
mean
middle value of a sample of results arranged in order of
increasing/decreasing magnitude.
Median
the value that occurs most frequently in a set of determinations.
Mode
describes the reproducibility of the measurements.
Precision
tells how close the results are, provided that they are obtained in exactly
the same way.
precision
deals with repeatability (within-runs) and reproducibility (between-runs).
precision
three terms are widely used to describe the precision of a set of replicate
data:
standard deviation
Variance
coefficient of variation.
indicates the closeness of the measurements to its true value
or accepted value and is expressed by the error (or simply the
proximity to the true value).
accuracy
accuracy is expressed in terms of
a. absolute error, E =| xi- xt|
b. relative error, Er = |xi- xt| / xi
what are the 3 types of error
random/indeterminate
systematic/determinate
gross
causes data to be scattered more or less systematically around a mean value.
affect measurement precision
Random / Indeterminate Error
causes the mean of a set of data to differ from the accepted value.
causes the results in a series of replicate measurements to be all high or low.
e.g. loss of a volatile analyte while heating a sample.
Systematic / Determinate Error
occur only occasionally, are often large and may cause a result to be either high or low.
often the product of human errors.
e.g. precipitate is lost before weighing;
e.g. touching a weighing bottle with your fingers after its empty mass is determined.
leads to outliers, results that obviously differ significantly from the rest of the data of
replicate measurements.
gross error
Sources of systematic errors
instrumental
method
personal
caused by nonideal instrument behavior, by faulty calibrations, or by use under
inappropriate conditions
caused by imperfection of measuring devices and instabilities in their power
supplies.
e.g glasswares used at temperatures that differ from their calibration temperature
distortion of container walls, errors in the original calibration, contaminants on the inner
surface of the containers
Calibration eliminates most systematic errors of this type.
Electronic instruments are also subject to systematic errors.
e.g. voltage of a battery- operated power supply decreases with use
e.g. instruments are not calibrated frequently or if they are calibrated incorrectly.
e.g. Temperature changes
Errors of these types are detectable and correctable.
instrumental error
arises from non-ideal chemical or physical behavior of analytical
systems.
chemical or physical behavior of the reagents and reactions.
due to slowness of some reactions
incompleteness of a reaction
instability of some species
nonspecificity of the reagents
possible occurrence of side reactions
method error
arises from non-ideal chemical or physical behavior of analytical
systems.
chemical or physical behavior of the reagents and reactions.
due to slowness of some reactions
incompleteness of a reaction
instability of some species
nonspecificity of the reagents
possible occurrence of side reactions
method error
results from the carelessness, inattention or personal limitations of the
experimenter.
estimating the level of the liquid between two scale divisions
the color of the solution at the end point in a titration
level of a liquid with respect to a graduation in a pipet or buret
personal error
Detection of Systematic Method Error:
a. analysis of standard samples
b. independent analysis
c. blank determination
d. variation in sample size
can be purchased from a number of governmental and
industrial sources (e.g. National Institute of Standards and
Technology, NIST which offers over 1300 SRMs)
Standard Reference Materials (SRM)
Concentration of the SRM has been determined in one of the
three ways:
- through analysis by previously validated reference method,
- through analysis by two or more independent, reliable measurement
methods, - through analysis by a network of cooperating laboratories, technically
competent and throughly knowledgeable with the material being tested.
a second independent and reliable analytical method to
be used in parallel with the method being evaluated.
🞑 should differ as much as possible from the method used.
🞑 This minimizes the possibility that some common factor in
the sample has the same effect on both methods.
independent analysis
a _______ contains the reagents and solvents used in a determination, but no analyte.
blank
useful for detecting certain types of constant errors.
all steps of the analysis are performed in the absence of the sample.
blank determination
many of the sample constituents are added to simulate the analyte environment, which is called the _______ (collection of
all the constituents in the sample).
sample matrix
can detect constant errors (as the size of
the measurement increases, the effect of a constant error decreases).
variation in sample size
Statistical Treatment of Random Errors
sample
population or universe
population mean, μ
sample mean
a finite number of experimental observations; a tiny fraction of infinite number of observations; subset of measurements selected from the population.
sample
the theoretical infinite number of data.
population
true mean of the population; in the
absence of any systematic error, this is also the true value for the measured quantity.
population mean
the mean of a limited sample drawn from the
population of the data
sample mean
Measures of precision
pop std
sample std
std of the mean
variance
relative std
coefficient of variation
spread or range
a measure of the precision of a population of data
pop std
a measure of the precision of a sample of data
sample std
the square of std
variance
the difference between the largest value and the smallest in the set of data.
spread or range
The exact value of the mean, μ, for a population of data can never be determined exactly because such a determination requires that an infinite number of measurements be made. Statistical theory, however, allows us to set limits around an
experimentally determined mean within which the population mean lies with a given degree of probability.
These limits are called _______, and the interval they define is known
as the ________
confidence limits; confidence interval
