LESSON 1: INTRODUCTION TO
ANALYTICAL CHEMISTRY
Analytical chemistry
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The Science of Chemical Measurements.
is a measurement science consisting of a set
of powerful ideas and methods that are
useful in all fields of science, engineering,
and medicine
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Types of Questions Asked in Analytical Chemistry
A. What is in the sample? (qualitative analysis)
- Qualitative analysis establishes the chemical
identity of the species in the sample.
B. How much is in the sample? (quantitative
analysis)
- Quantitative analysis determines the relative
amounts of these species, or analytes, in
numerical terms
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Techniques used in Analytical Chemistry:
A.
Wet Chemical Methods: titrations, colorforming reactions, precipitations, etc.
B. Instrumental Methods: spectrometry,
chromatography, etc.
Role of Analytical Chemistry
exhaust gases are measured to determine the
effectiveness of emission-control devices.
Quantitative measurements of ionized
calcium in blood serum help diagnose
parathyroid disease in humans.
Quantitative determination of nitrogen in
foods establishes their protein content and
thus their nutritional value.
Analysis of steel during its production
permits adjustment in the concentrations of
such elements as carbon, nickel, and
chromium to achieve a desired strength,
hardness, corrosion resistance, and ductility.
The mercaptan content of household gas
supplies is monitored continually to ensure
that the gas has a sufficiently obnoxious odor
to warn of dangerous leaks.
Farmers tailor fertilization and irrigation
schedules to meet changing plant needs
during the growing season, gauging these
needs from quantitative analyses of plants
and soil.
Quantitative Analytical Methods
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gravimetric methods
volumetric method
electroanalytical methods
spectroscopic methods
Flow diagram showing the steps in a quantitative
analysis
Application of Analytical Chemistry
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2.
The concentrations of oxygen and of carbon
dioxide are determined in millions of blood
samples every day and used to diagnose and
treat illnesses.
Quantities of hydrocarbons, nitrogen oxides,
and carbon monoxide present in automobile
The Analytical Process
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b.
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Formulating the Question: Translate General
Question into Specific Question
Choosing a Method
level of accuracy required
high reliability nearly always requires a large
investment of time.
The selected method usually represents a
compromise between the accuracy required
and the time and money available for the
analysis.
the number of samples that will be analyzed
the complexity of the sample and the number
of components in the sample always
influence the choice of method to some
degree.
Sampling:
a.) Select representative material to analyze
(i) don’t use the entire sample
(ii) consistency in sample collection
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Calibration is the process of determining the
proportionality
between
analyte
concentration and a measured quantity.
Calculating Results
data collected in the measurement step, the
characteristics
of
the
measurement
instruments, and the stoichiometry of the
analytical reaction
Evaluating Results by Estimating Reliability
analytical results are complete only when
their reliability has been estimated
LESSON 2: CALCULATIONS
ANALYTICAL CHEMISTRY
USED
IN
Units & SI System
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Units convey information and serve as guide
to solving problems
Fundamental Units
Derived Units
Acquiring the Sample
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When the bulk is large and heterogeneous,
great effort is required to get a representative
sample
An assay is the process of determining how
much of a given sample is the material by its
indicated name. For example, a zinc alloy is
assayed for its zinc content, and its assay is a
particular numerical value.
Sampling is the process of collecting a small
mass of a material whose composition
accurately represents the bulk of the material
being sampled.
Sampling is frequently the most difficult step
in an analysis and the source of greatest error
Processing the Sample
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Preparing a Laboratory Sample
Defining Replicate Samples
Preparing Solutions: Physical and Chemical
Changes
Eliminating Interferences
An interference or interferent is a species that
causes an error in an analysis by enhancing or
attenuating (making smaller) the quantity
being measured
Calibrating and Measuring Concentration
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Measurements based on SI system, which is
metric system
Metric Prefixes
Performing Unit Conversions
Solutions: Expressing Concentration
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Equilibrium concentrations expressed as
molarity
Analytical concentrations use formal
concentration
Analytical molarity is the total number of
moles of a solute, regardless of its chemical
state, in 1 L of solution. The analytical
molarity describes how a solution of a given
molarity can be prepared.
Equilibrium molarity is the molar
concentration of a particular species in a
solution.
Ex. 1.0 M H2SO4
Moles & Millimoles
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Mass versus Weight
Moles are the SI unit for amount of a
substance.
One mole of anything contains Avogadro’s
number of particles (chemical formula)
The mass of the Moon is only 1/81 that of
Earth and the acceleration due to gravity is
only 1/6 that on Earth.
The weight of the object on the Moon is only
1/6 of their weight on Earth.
Molar Mass is mass in grams of one mole of
a substance.
Calculate molar mass by summing atomic
masses of all elements in formula.
Often more convenient to use unit millimole
(Note: 1 mmole is equivalent to 10-3 mole)
Expression of concentration
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Molarity : M = (moles of solute) / (liter of
solution) = (mmoles) / (mL)
A mole is defined as the number of atoms of
12C in exactly 12 g of 12C (12 amu or
daltons).
Avogadro’s number = 6.0221438×1023.
A mole of a chemical species is
6.0221438×1023 atoms, molecules, ions,
electrons, ion pairs, or subatomic particles.
[H2SO4] = 0.00 M [H+] = 1.01 M
[HSO4–] = 0.99 M [SO4–2 ] = 0.01 M
Analytical molarity of H2SO4 is given by c H2SO4 =
[HSO4–] + [SO4–2 ]
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Percent Concentration
Mass (Weight)%
Volume %
Weight/volume %
Parts per Million (ppm)
Parts per Billion (ppb)
Percent composition
% = Weight % = w/w %
= {(mass of solute) / (mass of solution)} × 100 %
Volume % = v/v %
= {(volume of solute) / (volume of solution)} × 100 %
Weight / volume percent = w/v %
= {(weight of solute, g) / (volume of solution)} × 100
%
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Parts per million
ppm = (g / 106 g) ×106 ppm
= (mg/kg) ×106 ppm
= (μg/g) ×106 ppm
ppm (wt/v) = (mg/L) ×106 ppm
= (μg/mL) ×106 ppm
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Parts per billion
ppb = (g / 109 g) ×109 ppb
= (μg/L) ×109 ppb
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Parts per thousand
ppt = (g / 1000 g) ×103 ppt
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p-Functions
The p-value is the negative logarithm (to the
base 10) of the molar concentration of that
species.
pX = – log [X]
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density and specific gravity
Density = mass / volume
M1 V1 = M2 V2
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Stoichiometry
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Quantitative relationship among reactants &
products in a balanced chemical reaction.
Review Empirical vs. Molecular Formulas
Review Structural Formulas
LESSON 3: AQUEOUS SOLUTIONS AND
CHEMICAL EQUILIBRIA
Acids and Bases
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Conjugate Acids and Bases
Zwitterion
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Amphiprotic solvent
AUTOPROTOLYSIS
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Undergo self-ionization
STRENGTH OF ACIDS AND BASES
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Strong acids
Weak acids
CHEMICAL EQUILIBRIUM
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Equilibrium-constant expressions
Le Chatelier’s Principle
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LESSON 5: EFFECT OF ELECTROLYTES ON
CHEMICAL EQUILIBRIA
Activity & Ionic Strength
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Equilibrium constants for chemical reactions
should be written in terms of their activities
of participating species.
Activity is related to concentration by
activity coefficient.
Effect of added electrolyte is independent of
the chemical nature of electrolyte but
depends on ionic strength of solution.
Ionic Strength (u) = 0.5 ([A]ZA2 + [B]ZB2 +
[C]ZC2 …)
If one has a strong electrolyte consisting of
monovalent charged ions, the ionic strength
is identical to the total molar salt
concentration.
Ionic strength > molar-concentration if
solution contains ions with multiple charges.
(see Table 10.1)
Activity Coefficients
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Activity is related to concentration by
activity coefficient.
aX = [X] γX
Activity of a species is a measure of its
effective concentration as determined by
colligative properties, electrical conductivity,
and by mass action effect.
Review Properties of Activity Coefficients
(pp. 272-273)
Debye-Huckel Equation permits calculation
of activity coefficients of ions from their
charge and average size.
-log γA = 0.512 Z2X (u)1/2 / (1+ 3.3 αX
(u)1/2
Ordinarily we neglect activity coefficients
and simply use molar concentrations in
applications. Works most of the time.