basics of analytical chemistry and chemical equilibria

418 Pages·2013·4.18 MB·English

BASICS OF ANALYTICAL
CHEMISTRY AND
CHEMICAL EQUILIBRIA
BASICS OF ANALYTICAL
CHEMISTRY AND
CHEMICAL EQUILIBRIA
BRIAN M. TISSUE
VirginiaTech
DepartmentofChemistry
Blacksburg,VA
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Tissue,BrianM.,1961–
Basicsofanalyticalchemistryandchemicalequilibria / BrianM.Tissue.
pagescm
“PublishedsimultaneouslyinCanada”–Titlepageverso.
Includesindex.
ISBN978-0-470-59208-3(cloth)
1. Chemistry,Analytic–Textbooks. 2. Chemicalequilibrium–Textbooks. I.Title.
QD75.22.T572013
543–dc23
2013000336
PrintedintheUnitedStatesofAmerica.
10987654321
CONTENTS
PREFACE ix
I QUANTITATIVE ANALYSIS USING REACTIONS
THAT GO TO ‘‘COMPLETION’’ 1
1 MAKING MEASUREMENTS 3
1.1 Introduction / 3
1.2 GLP and a Few Other Important Acronyms / 10
1.3 Precision and Random Error / 15
1.4 Discarding a Suspected Outlier / 25
1.5 Calibration / 28
1.6 Maintaining Accurate Results / 43
Practice Exercises / 48
2 SAMPLE PREPARATION, EXTRACTIONS, AND
CHROMATOGRAPHY 53
2.1 Sampling and Control Samples / 53
2.2 Sample Preparation / 58
2.3 Solvents and Solutions / 64
2.4 Introduction to Solubility / 69
2.5 Extraction / 71
2.6 Stationary Phases / 82
v
vi CONTENTS
2.7 Solid-Phase Extraction (SPE) / 88
2.8 Introduction to Chromatography / 91
2.9 Immunoassays / 96
Practice Exercises / 97
3 CLASSICAL METHODS 103
3.1 Introduction / 103
3.2 Review of Chemical Reactions / 105
3.3 Reactions in Aqueous Solution / 111
3.4 Gravimetry / 120
3.5 Titration / 124
3.6 Titration Curves / 132
3.7 Coulometry / 134
Practice Exercises / 137
4 MOLECULAR SPECTROSCOPY 141
4.1 Introduction / 141
4.2 Properties of EM Radiation / 142
4.3 Electromagnetic Spectrum / 146
4.4 Spectroscopic Transitions / 147
4.5 UV/Vis Absorption Spectroscopy / 154
4.6 UV/Vis Instrumentation / 156
4.7 Beer–Lambert Law / 159
4.8 Molecular Fluorescence / 167
Practice Exercises / 171
II REACTIONS THAT DO NOT GO TO
‘‘COMPLETION.’’ EQUILIBRIA IN AQUEOUS
SOLUTIONS 177
5 ACID–BASE EQUILIBRIA AND ACTIVITY 179
5.1 Acids and Bases / 179
5.2 Weak Acids and Weak Bases / 186
5.3 Water and K / 190
w
5.4 Acid Strength / 196
5.5 The Concept of Activity / 199
5.6 Acid–Base Equilibrium Calculations / 212
Practice Exercises / 218
CONTENTS vii
6 BUFFER SOLUTIONS AND POLYPROTIC ACIDS 221
6.1 Buffer Solutions / 221
6.2 Alpha Fraction Plots / 226
6.3 Weak Acid Titration Curve / 230
6.4 Polyprotic Acids / 233
Practice Exercises / 242
7 COMPLEXATION AND PRECIPITATION EQUILIBRIA 245
7.1 Complex Terminology / 246
7.2 Complex Equilibria / 249
7.3 Competing Equilibria / 256
7.4 Stepwise Complexation / 263
7.5 Precipitate Equilibrium / 267
7.6 Molar Solubility / 275
7.7 Precipitation and Competing Equilibria / 282
Practice Exercises / 287
III INSTRUMENTAL METHODS AND ANALYTICAL
SEPARATIONS 293
8 ELECTROANALYTICAL CHEMISTRY 295
8.1 Introduction / 295
8.2 Standard Reduction Potentials / 298
8.3 Using Half Reactions / 302
8.4 Background on Spontaneous Reactions and Equilibrium / 308
8.5 Reaction Energies, Voltages, and the Nernst Equation / 311
8.6 Electrochemical Cells / 314
8.7 Potentiometry / 319
8.8 Ion-Selective Electrodes (ISE) / 322
8.9 Voltammetry / 328
Practice Exercises / 336
9 ATOMIC SPECTROMETRY 340
9.1 Atomization / 342
9.2 Atomic Absorption Spectrometry (AAS) / 346
9.3 Atomic Emission Spectrometry (AES) / 354
9.4 Introduction to Mass Spectrometry (MS) / 357
viii CONTENTS
9.5 ICP-MS Measurements / 361
9.6 Summary / 362
Practice Exercises / 364
10 ANALYTICAL SEPARATIONS 367
10.1 Thin-Layer Chromatography / 368
10.2 Chromatogram Terminology / 372
10.3 Column Selection / 375
10.4 High Performance Liquid Chromatography / 380
10.5 Gas Chromatography / 388
10.6 Molecular Mass Spectrometry / 390
10.7 Electrophoresis / 398
Practice Exercises / 402
INDEX 407
PREFACE
This text will introduce you to analytical chemistry: the science of making
quantitative measurements. Quantifying the individual components in a com-
plexsampleisanexerciseinproblemsolving.Aneffectiveandefficientanalyst
will have expertise in
• sampling, sample processing, and method validation;
• the chemistry that can occur in a sample before and during analysis;
• selecting an appropriate analytical method; and
• proper record keeping, data analysis, and reporting of results.
I do not attempt to be comprehensive in this text. Samples that require
analysis are so diverse that it is not possible to describe every sample prepa-
ration protocol, separation method, and measurement technique. These details
are contained in handbooks and method compilations, many of which are now
accessible from online sources. This text emphasizes the fundamental chemical
andphysicalconceptsthatunderlietheanalyticalmethods.Withanunderstand-
ing of the fundamental concepts, a scientist faced with a difficult analysis can
apply the most appropriate techniques, identify when a particular problem can-
not be solved with existing methods, and develop new analytical methods. The
proficient analyst will also be alert to interferences and problems in analytical
measurements and recognize when an “answer” might not be correct.
I organize the discussion of the core principles of analytical chemistry into
three parts:
• Part I: analytical concepts such as calibration and uncertainty, sample
preparation,classical(wet-chemical)methods,andmolecularUV/Visspec-
troscopy
ix
x PREFACE
• Part II: chemical equilibria involving acids, bases, complexes, and insolu-
ble precipitates
• Part III: electroanalytical methods, atomic and mass spectrometry, and
chromatographic separations
The analytical methods in Part I rely on reactions that go to completion.
Part II is a detailed treatment of chemical equilibria—reactions in which reac-
tants and products coexist. Equilibrium is critical to the functioning of many
aspectsofchemical,biochemical,andenvironmentalsystems.PartIIIdescribes
the most common instrumental methods of analysis, illustrating many of the
tools of the trade for making quantitative measurements. Even if your future
careerveersawayfromscience,youwillfindtheproblem-solvingandgraphical
data analysis skills developed in this text to be useful.
Many of the topics in this text follow directly from first-year college chem-
istry. You will want access to a general chemistry text or online resource to
refresh your memory of the principles that underlie the different types of reac-
tions and analytical methods. The level of this text presumes that you know
Basic math Algebra
Exponential functions
Calculating and plotting in a spreadsheet
Basic chemistry Predicting properties based on the periodic table
The nature of chemical compounds
Stoichiometry and balancing reactions
Reaction types Acid–base
Complexation
Precipitation
Reduction and oxidation (redox)
The beginning of each chapter lists learning outcomes that serve as a
brief outline to help categorize new material. After completing a chapter,
make a concept map to help yourself see the big picture and underlying
concepts. You will often encounter a repeat of concepts in the text. Making
connections with prior material makes learning analytical concepts much
easier. Treating every topic as something new becomes overwhelming. Each
chapter contains sample calculations and practice exercises. I assume that your
goal is success. Achieving success requires skills, and acquiring skills takes
practice.
Variables and constants are italicized to not be confused with other text.
As much as possible, I use the conventions and terminology in the IUPAC
PREFACE xi
Compendium of Chemical Terminology.1 You will find other symbols
in other books and resources, so use the context to decipher the differ-
ences. Relevant spreadsheets and links to useful resources are available at
http://www.basicsacce.com/ or http://www.files.chem.vt.edu/chem-ed/a-text/.
Blacksburg, VA Brian M. Tissue
May 2013
1See “IUPAC Compendium of Chemical Terminology–the Gold Book”. Available at
http://goldbook.iupac.org/. Accessed 2013 Feb 13.