BASICS OF ANALYTICAL CHEMISTRY AND CHEMICAL EQUILIBRIA
BASICS OF ANALYTICAL CHEMISTRY AND CHEMICAL EQUILIBRIA BRIAN M. TISSUE Virginia Tech Department of Chemistry Blacksburg, VA
Cover Design: Wiley Cover Illustration: Courtesy of Brian M. Tissue Copyright 2013 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com. Library of Congress Cataloging-in-Publication Data: Tissue, Brian M., 1961 Basics of analytical chemistry and chemical equilibria / Brian M. Tissue. pages cm Published simultaneously in Canada Title page verso. Includes index. ISBN 978-0-470-59208-3 (cloth) 1. Chemistry, Analytic Textbooks. 2. Chemical equilibrium Textbooks. I. Title. QD75.22.T57 2013 543 dc23 2013000336 Printed in the United States of America. 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 w / 190 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 complex sample is an exercise in problem solving. An effective and efficient analyst 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 preparation 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 and physical concepts that underlie the analytical methods. With an understanding of the fundamental concepts, a scientist faced with a difficult analysis can apply the most appropriate techniques, identify when a particular problem cannot 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, and molecular UV/Vis spectroscopy ix
x PREFACE Part II: chemical equilibria involving acids, bases, complexes, and insoluble 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 reactants and products coexist. Equilibrium is critical to the functioning of many aspects of chemical, biochemical, and environmental systems. Part III describes the most common instrumental methods of analysis, illustrating many of the tools of the trade for making quantitative measurements. Even if your future career veers away from science, you will find the problem-solving and graphical data analysis skills developed in this text to be useful. Many of the topics in this text follow directly from first-year college chemistry. 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 reactions and analytical methods. The level of this text presumes that you know Basic math Basic chemistry Reaction types Algebra Exponential functions Calculating and plotting in a spreadsheet Predicting properties based on the periodic table The nature of chemical compounds Stoichiometry and balancing reactions 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 differences. 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 1 See IUPAC Compendium of Chemical Terminology the Gold Book. Available at http://goldbook.iupac.org/. Accessed 2013 Feb 13.