Laboratory manual for principles of general chemistry 9th edition 1

This page intentionally left blank ffirs.qxd 9/1/10 4:37 PM Page i Laboratory Manual for Principles of General Chemistry This page intentionally left blank ffirs.qxd 9/1/10 4:37 PM Page iii Laboratory Manual for Principles of General Chemistry Ninth Edition J A Beran Regents Professor, Texas A&M University System Texas A & M University—Kingsville John Wiley & Sons, Inc ffirs.qxd 9/1/10 4:37 PM Page iv The author of this manual has outlined extensive safety precautions in each experiment Ultimately, it is your responsibility to practice safe laboratory guidelines The author and publisher disclaim any liability for any loss or damage claimed to have resulted from, or been related to, the experiments PUBLISHER Kaye Pace ASSOCIATE PUBLISHER Petra Recter ACQUISITIONS EDITOR Nick Ferrari PROJECT EDITOR Jennifer Yee PRODUCTION MANAGER Dorothy Sinclair PRODUCTION EDITOR Erin Bascom MARKETING MANAGER Kristine Ruff CREATIVE DIRECTOR Harry Nolan SENIOR DESIGNER Kevin Murphy PRODUCTION MANAGEMENT SERVICES MPS Limited SENIOR ILLUSTRATION EDITOR Anna Melhorn MANAGER, PHOTO DEPARTMENT Hilary Newman EDITORIAL ASSISTANT Cathy Donovan MEDIA EDITOR Thomas Kulesa COVER PHOTO ©Stuart Gregory/Getty Images, Inc This book was set in Times New Roman by MPS Limited, and printed and bound by Courier Westford The cover was printed by Courier Westford This book is printed on acid free paper ࠗ ȍ Copyright ᭧ 2011, 2009 John Wiley & Sons, Inc All rights reserved 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 Sections 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, website 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 07030-5774, (201) 748-6011, fax (201) 748-6008, website http://www.wiley.com/go/permissions Evaluation copies are provided to quali ed academics and professionals for review purposes only, for use in their courses during the next academic year These copies are licensed and may not be sold or transferred to a third party Upon completion of the review period, please return the evaluation copy to Wiley Return instructions and a free of charge return shipping label are available at www.wiley.com/go/returnlabel Outside of the United States, please contact your local representative Library of Congress Cataloging-in-Publication Data Beran, Jo A Laboratory manual for principles of general chemistry / J.A Beran — 9th ed p cm ISBN 978-0-470-64789-9 (pbk.) Chemistry—Laboratory manuals I Title QD45.B475 2010 542—dc22 2010026597 Printed in the United States of America 10 fpref.qxd 9/3/10 1:40 PM Page v Preface Chemistry laboratories have changed with advances in technology and safety issues Welcome to the ninth edition! Writing the ninth edition has been the most challenging of the nine editions of this manual The eighth edition was one of the most successful laboratory manuals that Wiley has ever produced for general chemistry Reviewers’ comments were supportive of the challenges and format offered in the eighth edition with only a handful of suggestions—the experiments are interesting, challenging, and have good pedagogy regarding laboratory techniques, safety, and experimental procedures The reporting and analyzing of data and the questions (pre- and post-lab) sought to focus on the intuitiveness of the experiment The challenge for the ninth edition was to improve on what already appeared to be the general chemistry laboratory manual that “students and faculty want and expect.” Consequently, the “good” from the eighth has been retained, but added depth, relevance, and appreciation of the laboratory experience has been intertwined Trends toward safer, more modern laboratory equipment, computer usage, and online information are included The open-endedness of each experiment is encouraged in “The Next Step” where, on completion of the experiment, the student has the tools and experience to employ for studying additional chemical systems or topics of his or her interest It is hoped that laboratory instructors and students will add their own Next Step for pursuing personal areas of interest and investigation The Front Cover: The front cover for this ninth edition was chosen to convey the message to students that this laboratory experience is not as an end in itself Rather, as the sun rises to begin a new day, so does the dawn of careers in science, beginning with hands-on involvement into scienti c investigations in the laboratory We wish for students to use scienti c logic and quantitative analysis to account for the observed chemical phenomena Ultimately, we hope these experiences will provide them a strong, basic foundation on which they can build their professional careers, whether they become chemists, biologists, medical- eld scientists, or professional chefs While all comments of users and reviewers from the previous eight editions have been heavily weighed with each new edition, the task of presenting the “perfect” manual, like chemistry and science in general, is impossible However, at this point in time, we feel it is the “best” that it can be Breadth (and Level) of the Ninth Edition This manual covers two semesters (or three quarters) of a general chemistry laboratory program A student may expect to spend three hours per experiment in the laboratory; limited, advanced preparation and/or extensive analysis of the data may lengthen this time The experiments were chosen and written so that they may accompany any general chemistry text Features of the Ninth Edition Safety and Disposal “Safety rst” is again emphasized throughout the manual, with recent advisories and guidelines being added Laboratory Safety and Guidelines outlines personal and laboratory safety rules and issues Icons in the Experimental Procedures cite Cautions for handling various chemicals, the proper Disposal of chemicals, and the proper Cleanup of laboratory equipment Prelaboratory Assignment questions often ask students to review the safety issues for the experiment Preface v fpref.qxd 9/3/10 1:40 PM Page vi Laboratory Techniques Numbered icons cited at the beginning of each experiment and within the Experimental Procedure are referenced to basic laboratory techniques that enable the student to complete the experiment more safely and ef ciently The Laboratory Techniques section provides a full explanation of 17 basic general chemistry laboratory techniques (along with the corresponding icons) that are used throughout the manual Each of the techniques has been closely edited, with one from the eighth edition omitted because it is not cited in the Experimental Procedures of the manual Organization For the eighth edition, the experiments were categorized according to subject matter This format was widely accepted by users and reviewers and retained in the ninth edition For example, all redox experiments are grouped in Part E such that the sequential numbering of the experiments within Part E indicates a greater degree of complexity Experiment 27, Oxidation–Reduction Reactions, is the simplest of the experiments involving oxidation–reduction reactions, not the 25th most dif cult experiment in the manual, and Experiment 33, Electrolytic Cells: Avogadro’s Number, is perhaps the most dif cult of the oxidation–reduction experiemnts Report Sheets Report Sheets are more user-friendly! Data entries on the Report Sheet are distinguished from calculated entries—the calculated entries are shaded on the Report Sheet Students also are encouraged to engage appropriate software for analyzing and plotting data Additionally, at the discretion of the instructor, the web site www.wiley.com/college/chem/brean provides downloadable Excel Report Sheet templates for each experiment where a numerical analysis is required Online References A signi cant number of web sites are cited in various experiments and dry labs An extensive list of online references is also provided in the Laboratory Data section of the manual New to the Ninth Edition Prelaboratory Assignment and Laboratory Questions Perhaps the most evident revisions appear in the questions in the Prelaboratory Assignments and the Laboratory Questions More than one-half of the questions are new to the ninth edition, and all of the questions were reviewed for clarity Revised Experiments All of experiments from the eighth edition have been retained but have been addressed for clarity in the Experimental Procedures for obtaining good data while using proper chemical techniques and on the Report Sheet for recording and analyzing data These re nements have become increasingly important for today’s students who continue to develop, in general, a multitude of state-of-the-art electronic skills The Next Step The Next Step is a feature added to the eighth edition and has been met with anticipated inclusion into open-ended laboratory programs Based on the tools and techniques gained with completion of the experiment, The Next Step takes students from its completion to ideas for an independent, self-designed experience or experiment The Next Step was developed to answer the student’s question, “What more can I now with what I just learned in the laboratory?” Scienti c inquiry of the chemical system begins with The Next Step when the student leaves the laboratory, it does not end with “Well, that experiment is over!” Laboratory Equipment Simple laboratory glassware and equipment, shown in the early sections of the manual, are necessary for completing most experiments Where appropriate, the apparatus or technique is shown in the experiment with a line drawing or photograph Analytical balances, spectrophotometers (Experiments 34 and 35), pH meters (Experiment 18), and multimeters (Experiments 32 and 33) are suggested; however, if this instrumentation is unavailable, these experiments can be modi ed without penalizing students In general, hot plates have largely replaced Bunsen burners in the manual; however if not available, the Bunsen ame can still be safely used for heating Contents of the Ninth Edition The manual has ve major sections: • Laboratory Safety and Guidelines Information on self-protection, what to in case of an accident, general laboratory rules, and work ethics in the laboratory are presented vi Laboratory Manual for Principles of General Chemistry fpref.qxd 9/3/10 1:40 PM Page vii • Laboratory Data Guidelines for recording and reporting data are described Sources of supplementary data (handbooks and World Wide Web sites) are listed Suggestions for setting up a laboratory notebook are presented • Laboratory Techniques Seventeen basic laboratory techniques present the proper procedures for handling chemicals and apparatus Techniques unique to qualitative analysis (Experiments 37–39) are presented in Dry Lab • Experiments and Dry Labs Thirty-nine experiments and four “dry labs” are subdivided into 12 basic chemical principles • Appendices Seven appendices include conversion factors, the treatment of data, the graphing of data, names of common chemicals, vapor pressure of water, concentrations of acids and bases, and water solubility of inorganic salts Contents of Each Experiment Each experiment has six sections: • Objectives One or more statements establish the purposes and goals of the experiment The “ avor” of the experiment is introduced with an opening photograph • Techniques Icons identify various laboratory techniques that are used in the Experimental Procedure The icons refer students to the Laboratory Techniques section where the techniques are described and illustrated • Introduction The chemical principles, including appropriate equations and calculations that are applicable to the experiment, and general interest information are presented in the opening paragraphs New and revised illustrations have been added to this section to further enhance the understanding of the chemical principles that are used in the experiment • Experimental Procedure The Procedure Overview, a short introductory paragraph, provides a perspective of the Experimental Procedure Detailed, stepwise directions are presented in the Experimental Procedure Occasionally, calculations for amounts of chemicals to be used in the experiment must precede any experimentation • Prelaboratory Assignment Questions and problems about the experiment prepare students for the laboratory experience The questions and problems can be answered easily after studying the Introduction and Experimental Procedure Approximately 60 percent of the Prelaboratory questions and problems are new to the ninth edition • Report Sheet The Report Sheet organizes the observations and the collection and analysis of data Data entries on the Report Sheet are distinguished from calculated (shaded) entries Laboratory Questions, for which students must have a thorough understanding of the experiment, appear at the end of the Report Sheet Approximately 50 percent of the Laboratory Questions are new to the ninth edition Instructor’s Resource Manual The Instructor’s Resource Manual (available to instructors from Wiley) continues to be most explicit in presenting the details of each experiment Sections for each experiment include • • • • • • • • • an Overview of the experiment an instructor’s Lecture Outline Teaching Hints representative or expected data and results Chemicals Required Special Equipment Suggested Unknowns answers to the Prelaboratory Assignment questions and Laboratory Questions a Laboratory Quiz Offered as a supplement to the Instructor’s Resource Manual is a Report Sheet template for those experiments requiring the numerical analysis of data The format of the templates is based on Microsoft Excel software and is available from Wiley on adoption The Appendixes of the Instructor’s Resource Manual detail the preparation of all of the solutions, including indicators, a list of the pure substances, and a list of the special equipment used in the manual and the corresponding experiment number for each listing Users of the laboratory manual have made mention of the value of the Instructor’s Resource Manual to the laboratory package Preface vii fpref.qxd 9/3/10 1:40 PM Page viii Reviewers The valuable suggestions provided by the following reviewers for this ninth edition are greatly appreciated: Steven E Czerwinski Harford Community College Jeanne Domoleczny Benedictine University Phillip DeLassus University of Texas—Pan American Dimitrios Giarikos Nova Southeastern University Todor Gounev University of Missouri—Kansas City Stephen Z Goldberg Adelphi University Michael Schuder Carroll University Acknowledgments The author thanks Dr John R Amend, Montana State University, for permission to use his basic idea in using emission spectra (without the aid of a spectroscope) to study atomic structure (Dry Lab 3); Dr Gordon Eggleton, Southeastern Oklahoma State University, for encouraging the inclusion of the paper chromatography experiment (Experiment 4); the general chemistry faculty at Penn State University, York Campus for the idea behind the thermodynamics experiment (Experiment 26); and to Dr Stephen Goldberg, Adelphi University, for his insightful chemical and editorial suggestions and opinions throughout the writing of the ninth edition What a staff at Wiley! Thanks to Jennifer Yee, Project Editor, for her keen insight, helpful suggestions, and unending commitment to see the manual through its birth; Erin Bascom, Production Editor, for coordinating the production of the manual; Hilary Newman, Photo Editor at Wiley, for assistance in obtaining the photographs for this edition; Kevin Murphy, Senior Designer; Anna Melhorn, Illustration Coordinator; Kristine Ruff, Marketing Manager; Cathy Donovan, Editorial Program Assistant; and Lynn Lustberg, Project Manager Thanks also to the Chemistry 1111 and 1112 students, and laboratory assistants and staff at Texas A&M—Kingsville for their keen insight and valuable suggestions; also to my colleagues and assistants for their valuable comments A special note of appreciation is for Judi, who has unsel shly permitted me to follow my professional dreams and ambitions since long before the rst edition of this manual in 1978 She has been the “rock” in my life And also to Kyle and Greg, who by now have each launched their own families and careers—a Dad could not be more proud of them and their personal and professional accomplishments My father and mother gave their children the drive, initiative, work ethic, and their blessings to challenge the world beyond that of our small Kansas farm I shall be forever grateful to them for giving us those tools for success James E Brady, St Johns University, Jamaica, NY, who was a coauthor of the manual in the early editions, remains the motivator to review and update the manual and to stay at the forefront of general chemistry education Gary Carlson, my rst chemistry editor at Wiley, gave me the opportunity to kick off my career in a way I never thought possible or even anticipated Thanks Jim and Gary The author invites corrections and suggestions from colleagues and students J A Beran Regents Professor, Texas A&M University System MSC 161, Department of Chemistry Texas A&M University—Kingsville Kingsville, TX 78363 viii Laboratory Manual for Principles of General Chemistry exp12.qxd 9/3/10 6:46 PM Page 172 a How is the pressure of the vaporized liquid determined in this experiment? b How is the volume of the vaporized liquid determined in this experiment? c How is the temperature of the vaporized liquid determined in this experiment? d How is the mass of the vaporized liquid determined in this experiment? The molar mass of a compound is measured to be 30.7, 29.6, 31.1, and 32.0 g/mol in four trials a What is the average molar mass of the compound? b Calculate the standard deviation and the relative standard deviation (as %RSD) (see Appendix B) for the determination of the molar mass 172 Molar Mass of a Volatile Liquid exp12.qxd 9/3/10 6:46 PM Page 173 Experiment 12 Report Sheet Molar Mass of a Volatile Liquid Date Lab Sec Name Desk No A Preparing the Sample Trial Unknown number _ Mass of dry ask, foil, and rubber band ( g) Trial Trial _ B Vaporize the Sample Temperature of boiling water (ЊC, K) _ _ _ Mass of dry ask, foil, rubber band, and vapor ( g) _ _ _ C Determine the Volume and Pressure of the Vapor Volume of 125-mL ask ( L) _ ϩ _ ϩ _ ϭ total volume _ Atmospheric pressure (torr, atm) _ D Calculations Moles of vapor, nvapor (mol) _ _ _ Mass of vapor, mvapor (g) _ _ _ Molar mass of compound (g/mol) _* _ _ Average molar mass (g/mol) _ Standard deviation of molar mass _ Appendix B Relative standard deviation of molecular mass (%RSD) _ Appendix B *Calculation of Trial Show work here Class Data/Group Molar mass Sample unknown no _ Experiment 12 173 exp12.qxd 9/3/10 6:46 PM Page 174 Calculate the standard deviation and the relative standard deviation (as %RSD) of the molar mass of the unknown for the class See Appendix B (Optional) Ask your instructor for the name of your unknown liquid Using van der Waals’ equation and the values of a and b for your compound, repeat the calculation for the moles of vapor, nvapor (show for Trial below), to determine a more accurate molar mass of the compound E Calculations (van der Waals’ equation) Trial 1* Trial Trial Moles of vapor, nvapor (mol) _ _ _ Mass of vapor, mvapor (g) _ _ _ Molar mass of compound (g/mol) _ _ _ Unknown number a ϭ , b ϭ Average molar mass (g/mol) _ *Calculation of nvapor from van der Waals’ equation for Trial Show work here Laboratory Questions Circle the questions that have been assigned Part A.1 The mass of the ask ( before the sample in placed into the ask) is measured when the outside of the ask is wet However, in Part B.3, the outside of the ask is dried before its mass is measured a Will the mass of vapor in the ask be reported as too high or too low, or will it be unaffected? Explain b Will the molar mass of vapor in the ask be reported as too high or too low, or will it be unaffected? Explain Part A.1 From the time the mass of the ask is rst measured in Part A.1 until the time it is nally measured in Part B.3, it is handled a number of times with oily ngers Does this lack of proper technique result in the molar mass of the vapor in the ask being reported as too high or too low or as unaffected? Explain Part B.2 The ask is completely lled with vapor only when it is removed from the hot water bath in Part B.3 However, when the ask cools, some of the vapor condenses in the ask As a result of this observation, will the reported molar mass of the liquid be too high or too low or as unaffected? Explain Part B.2 Suppose the thermometer is miscalibrated to read 0.3°C higher than actual Does this error in calibration result in the molar mass of the vapor in the ask being reported as too high or too low or as unaffected? Explain Part C.1 If the volume of the ask is assumed to be 125 mL instead of the measured volume, would the calculated molar mass of the unknown liquid be too high or too low or as unaffected by this experimental error? Explain Part C.2 The pressure reading from the barometer is recorded higher than it actually is How does this affect the reported molar mass of the liquid: too high, too low, or unaffected? Explain 174 Molar Mass of a Volatile Liquid exp13.qxd 9/1/10 3:40 PM Page 175 Experiment 13 A Carbonate Analysis; Molar Volume of Carbon Dioxide The reaction of hydrochloric acid on calcium carbonate produces carbon dioxide gas • To determine the percent calcium carbonate in a heterogeneous mixture • To determine the molar volume of carbon dioxide gas at 273 K and 760 torr Objectives Heterogeneous mixture: a nonuniform mix of two or more substances, oftentimes in different phases The following techniques are used in the Experimental Procedure: Techniques Calcium carbonate is perhaps the most prevalent simple inorganic compound in Earth’s crust More commonly known as limestone, calcium carbonate is found in many forms and formulations Chalk, marble (a dense form of calcium carbonate), shells of shell sh, stalactites, stalagmites (Figure 13.1), caliche, and the minerals responsible for hard water have their origin from fossilized remains of marine life In this experiment, the percent by mass of a carbonate salt in a heterogeneous mixture is determined Your instructor may choose anhydrous calcium carbonate, anhydrous sodium carbonate, or potassium carbonate as the salt For each of the carbonates, the same chemistry and analysis applies The focus of the Introduction is on calcium carbonate Calcium carbonate readily reacts in an acidic medium to produce carbon dioxide gas: Introduction CaCO3(s) ϩ H3Oϩ(aq) l Ca2ϩ(aq) ϩ H2O(l) ϩ CO2(g) (13.1) The calcium carbonate of the sample is treated with an excess of hydrochloric acid, and the carbon dioxide gas is collected over water The moles of carbon dioxide generated in the reaction are measured and, from the stoichiometry of equation 13.1, the moles and mass of CaCO3 in the sample are calculated Because carbon dioxide is relatively soluble in water, the water over which the CO2 is collected is pretreated to saturate it with carbon dioxide In addition to analyzing the unknown mixture for percent calcium carbonate and impurities, the molar volume of carbon dioxide is also determined At standard temperature and pressure (STP), one mole of an ideal gas occupies 22.4 L; that is, its molar volume is 22.4 L at STP Because carbon dioxide is not an ideal gas, we may expect its molar volume to vary slightly from this number To make these two determinations in the experiment, two important measurements are made: (1) The CO2 gas evolved from the reaction is collected and its volume is measured, and (2) the mass difference of the CaCO3 mixture, before and after reaction, is also measured Figure 13.1 Stalagmites and stalactites are primarily calcium carbonate Molar volume: volume occupied by one mole (6.023 ϫ 1023 atoms or molecules) of gas at defined temperature and pressure conditions Standard temperature and pressure: 273 K (0ЊC) and atmosphere (760 torr) Experiment 13 175 exp13.qxd 9/1/10 3:40 PM Page 176 Molar Volume of Carbon Dioxide The mass loss of the CaCO3 mixture is due to the mass of CO2(g) evolved in the reaction; the mass of CO2 is converted to moles of CO2 evolved The volume of CO2(g), collected over water under the temperature and pressure conditions of the experiment, is calculated at STP conditions (see equation 13.4) Knowing the number of moles and the volume at STP, the molar volume of CO2(g) is calculated VCO2(STP) (13.2) ϭ molar volume of CO2 nCO2 Volume of Collected Carbon Dioxide at STP The CO2(g) evolved in the reaction is collected by displacing an equal volume of water [Figure 13.2 (top)] Because the CO2(g) is bubbled through the water, it is considered “wet,” meaning that the volume occupied by the CO2(g) is also saturated with water vapor at the temperature of the water over which it is collected Therefore, the total pressure, PT, in this volume is due to the combined pressures of the CO2 gas, pCO2, and the water vapor, pH2O The pressure of the dry CO2 is calculated using Dalton’s law of partial pressures For carbon dioxide gas, Dalton’s law of partial pressures: The total pressure, PT, exerted by a mixture of gases is the sum of the individual pressures (called partial pressures) exerted by each of the constituent gases pCO2 ϭ PT Ϫ pH2O (13.3) The pressure of the water vapor, pH2O, at the gas-collecting temperature (obtained from Appendix E) is subtracted from the total pressure of the gases, PT, in the gascollecting vessel Experimentally, the total pressure of the gaseous mixture (CO2 ϩ H2O) is adjusted to atmospheric pressure (PT ϭ Patm) by adjusting the water levels inside and outside the gas-collecting vessel to be equal [Figure 13.2 (bottom)] Atmospheric pressure is read from the laboratory barometer Once the experimental values for the volume, pressure, and temperature of the CO2(g) are determined, the volume of CO2(g) at STP conditions is calculated using a combination of Boyle’s law (P ϰ 1/V ) and Charles’ law (V ϰ T) VCO2(at STP) ϭ VCO2 expt ϫ ΂ pCO2 expt(torr) 760 torr Boyle’s law correction Figure 13.2 The collection of CO2 gas over water (top) and the pressure measurement of “wet” CO2 gas (bottom) Percent Calcium Carbonate in Mixture ΃ ϫ ΂T 273 K(K)΃ Charles’ law correction This value is used in equation 13.2 In addition to the fact that the collected CO2(g) is wet, CO2 also has an appreciable solubility in water When the CO2(g) is bubbled through pure water, some of the CO2 dissolves in the water and is not measured as gas evolved in the reaction To minimize any loss of evolved CO2 as a result of its water solubility, the water is saturated with CO2 before the experiment is conducted This saturation is completed with the addition of either sodium bicarbonate to slightly acidi ed water or an antacid tablet that evolves CO2, such as Alka-Seltzer By use of equation 13.1, once the moles of CO2(g) evolved in the reaction is known, the moles and mass of CaCO3 in the heterogeneous mixture can be calculated The percent CaCO3 in the mixture is calculated by dividing this mass of CaCO3 by that of the original mixture and multiplying by 100: mass of CaCO3 ϫ 100 ϭ % CaCO3 mass of mixture Experimental Procedure 176 (13.4) CO2 expt (13.5) Procedure Overview: A gas generator is constructed to collect the CO2(g) evolved from a reaction The masses of the sample in the gas generator before and after the reaction are measured; the volume of CO2(g) evolved in the reaction is collected and measured A Carbonate Analysis; Molar Volume of Carbon Dioxide exp13.qxd 9/1/10 3:40 PM Page 177 Two trials are required in this experiment To hasten the analyses, prepare two samples for Part A and perform the experiment with a partner Obtain an unknown calcium carbonate sample from your instructor Record the sample number Water saturated with CO2 Fill a 1-L beaker with tap water and saturate the water with CO2 using one Alka-Seltzer tablet.1 Save for Part A.3 Sample preparation a Mass of heterogeneous sample Calculate the mass of CaCO3 that would produce ϳ40 mL of CO2 at STP See Prelaboratory Assignment question and show the calculation on the Report Sheet On weighing paper, measure this calculated mass (Ϯ0.001 g) of the sample mixture, one that contains CaCO3 and a noncarbonate impurity Carefully transfer the sample to a 75-mm test tube b Set up the CO2 generator Place 10 mL of M HCl in a 200-mm test tube; carefully slide the 75-mm test tube into the 200-mm test tube without splashing any of the acid into the sample Important: The HCl(aq) is in the 200-mm test tube and separately, but inserted, the CaCO3(s) sample is in the 75-mm test tube Do not mix the two substances until Part B.1! c Mass of CO2 generator Measure the combined mass (Ϯ0.001 g) of this CO2 generator (Figure 13.3) Setup of CO2 collection apparatus a Saturated water with CO2 Fill the pan (Figure 13.4) about two-thirds full with the water that is saturated with CO2 (Part A.1) Do not proceed in the experiment until the CO2 from the Alka-Seltzer is no longer evolved b Fill CO2(g)-collecting graduated cylinder Use the CO2-saturated water in the pan to ll the 50-mL graduated cylinder that will collect the CO from the sample Fill the graduated cylinder by laying it horizontal in the water, and then, without removing the mouth of the cylinder from the water, set it upright c Connect the gas inlet tube Place the gas inlet tube (connect to rubber or Tygon tubing) that connects to the CO2 generator into the mouth of the 50-mL CO2(g)collecting graduated cylinder Support the graduated cylinder with a ring stand and clamp Read and record the water level in the graduated cylinder (if no air entered the cylinder, it should read zero) Note that the graduation marks on the cylinder are now upside down—be careful in reading and recording the volume A Sample Preparation and Setup of Apparatus Figure 13.3 Apparatus for measuring the combined mass of the CO2 generator Figure 13.4 A CO2 gas-collection apparatus An acidic solution of sodium bicarbonate can also be used to saturate the water with CO2 Experiment 13 177 exp13.qxd 9/1/10 3:40 PM Page 178 Figure 13.5 A CO2 gas generator Figure 13.6 Equalizing the pressure in the test tube to atmospheric pressure Setup of CO2 generator Prepare a one-hole rubber stopper (check to be certain there are no cracks in the rubber stopper) tted with a short piece of glass tubing and rmly insert it into the 200-mm test tube to avoid any leaking of CO2(g) from the reaction Clamp the CO2 generator (200-mm test tube) to the ring stand at a 45Њ angle from the horizontal (Figure 13.5) Connect the gas delivery tube from the CO2 collection apparatus (Figure 13.4) to the CO2 generator (Figure 13.5) Obtain instructor’s approval Obtain your instructor’s approval before continuing B Collection of the Carbon Dioxide Gas Generate and collect the CO2(g) Initiate the reaction Gently agitate the generator (Figure 13.5) to allow some of the HCl solution to contact the sample mixture As the evolution rate of CO2(g) decreases, agitate again and again until CO2(g) is no longer evolved C Determination of the Volume, Temperature, and Pressure of the Carbon Dioxide Gas Determine the volume of CO2(g) evolved When no further generation of CO2(g) is evident in the gas-collection apparatus (Figure 13.4), and while it is still in the water- lled pan, adjust the CO 2(g)-collecting graduated cylinder so that the water levels inside and outside of the graduated cylinder are equal (Figure 13.6) Read and record the nal volume of gas collected in the graduated cylinder Determine the temperature of CO2(g) Read and record the temperature of the water in the pan Determine the pressure of the CO2(g) a When the water levels inside and outside of the graduated cylinder are equal, the pressure of the wet CO2(g) equals atmospheric pressure b Read and record the barometric pressure in the laboratory Obtain the vapor pressure of water at the gas-collecting temperature in Appendix E to calculate the pressure of the dry CO2(g) evolved in the reaction Appendix E D Mass of Carbon Dioxide Evolved The Next Step 178 Determine a mass difference Determine the mass (Ϯ0.001 g) of the 200-mm CO2 generator and its remaining contents Compare this mass with that in Part A.2c After subtracting for the mass of the generator, calculate the mass loss of the sample The analysis for the percent aluminum in an aluminum container can be completed using the same technique, a reaction of aluminum metal with hydrochloric acid Research and design an experimental procedure for its analysis A Carbonate Analysis; Molar Volume of Carbon Dioxide exp13.qxd 9/1/10 3:40 PM Page 179 Experiment 13 Prelaboratory Assignment A Carbonate Analysis; Molar Volume of Carbon Dioxide Date Lab Sec Name Desk No In some solid calcium carbonate samples, calcium bicarbonate, Ca(HCO3)2, is also present Write a balanced equation for its reaction with hydrochloric acid Experimental Procedure, Part A.2a Complete the calculation required to appear on the Report Sheet (here and on Report Sheet) a Experimental Procedure, Part A.3b Explain how a water- lled graduated cylinder is inverted in a pan of water b Experimental Procedure, Part A.4 What is the proper procedure for inserting a piece of glass tubing into a rubber stopper? Experimental Procedure, Part C.1 How is the volume of the CO2(g) collected (over water) measured in this experiment? A thermometer is not present in the space (or volume) in which the CO2(g) is collected in this experiment a How then is the temperature of the CO2(g) determined in this experiment? b The mass of a gas is elusive How is the mass of the CO2(g) collected over water determined in this experiment? Experiment 13 179 exp13.qxd 9/1/10 3:40 PM Page 180 A 0.276-g sample of a CaCO3 heterogeneous mixture was placed into a gas generator, the total mass of which is 87.719 g (containing the CaCO3 sample and the beaker, an HCl solution, and test tubes; see Figure 13.3) is connected to a gas-collection apparatus (Figure 13.4) The following data were collected following the reaction (equation 13.1): Volume of wet CO2 Temperature of wet CO2 Pressure of wet CO2 Mass of gas generator after reaction 37.7 mL 20.0ЊC 770 torr 87.642 g Express all subsequent calculations to the correct number of signi cant gures a Determine the mass and moles of CO2 evolved in the reaction Hint: What is the mass difference of the gas generator? b Determine the pressure of the dry CO2 See equation 13.3 c Calculate the volume of the dry CO2 at STP See equation 13.4 d What is the calculated molar volume of the dry CO2? See equation 13.2 e How many moles of CaCO3 produced the moles of CO2 in the reaction? See equation 13.1 f Determine the mass of CaCO3 in the original mixture g What is the percent (by mass) CaCO3 in the original mixture? See equation 13.5 180 A Carbonate Analysis; Molar Volume of Carbon Dioxide exp13.qxd 9/1/10 3:40 PM Page 181 Experiment 13 Report Sheet A Carbonate Analysis; Molar Volume of Carbon Dioxide Date Lab Sec Name Desk No A Sample Preparation and Setup Apparatus Calculation of mass of CaCO3 sample for analysis Trial Trial Mass of sample (g) Mass of generator ϩ sample before reaction (g) Unknown sample no Instructor’s approval of apparatus C Determination of Volume, Temperature, and Pressure of the Carbon Dioxide Gas Initial volume of water in CO2-collecting graduated cylinder (mL) Final volume of water in CO2-collecting graduated cylinder (mL) Volume of CO2(g) collected (L) Temperature of water (ЊC) Barometric pressure (torr) Vapor pressure of H2O at _ЊC (torr) Pressure of dry CO2(g) (torr) Mass of generator ϩ sample after reaction (g) Mass loss of generator ϭ mass CO2 evolved (g) D Mass of Carbon Dioxide Evolved Experiment 13 181 exp13.qxd 9/1/10 3:40 PM Page 182 Trial Trial Pressure of dry CO2(g) (atm) See Part C.7 Volume of CO2(g) at STP (L) See equation 13.4 Moles of CO2(g) generated (mol) Molar volume of CO2(g) at STP (L/mol) See equation 13.2 E Molar Volume of CO2 Gas Average molar volume of CO2(g) at STP (L/mol) F Percent CaCO3 in Mixture Moles of CaCO3 in sample from mol CO2 generated (mol) See equation 13.1 Mass of CaCO3 in sample (g) Mass of original sample (g) Percent of CaCO3 in sample (%) Average percent of CaCO3 in sample (%) Laboratory Questions Circle the questions that have been assigned Part A.1 The water for the pan (Part A.3) is not saturated with CO2 Will the reported percent CaCO3 in the original sample be too high, too low, or unaffected? Explain Part A.2 Suppose M HCl is substituted for the M HCl in the procedure What would be the consequence of this substitution? Explain Part A.2 If some of the CaCO3 in the sample had already formed some Ca(HCO3)2, will the volume of CO2(g) generated in the reaction be greater than, less than, or the same as in the experiment? Explain Part A.3 A few drops of HCl(aq) spilled over into the CaCO3 sample prior to rmly seating the stopper and prior to collecting any CO2(g) As a result of this poor technique, will the reported percent CaCO3 in the sample be too high, too low, or unaffected? Explain Part C.1 The water level in the CO2(g)-collection cylinder is higher than the water level outside the cylinder a Is the wet CO2 gas pressure greater or less than atmospheric pressure? Explain b An adjustment is made to equilibrate the water levels Will the volume of the wet CO2 gas increase or decrease? Explain c The student chemist chooses not to equilibrate the inside and outside water levels Will the reported number of moles of CO2 generated in the reaction be too high, too low, or unaffected by this carelessness? Explain Part C.1 An air bubble accidentally enters the CO2-collection graduated cylinder after the completion of the reaction How does this error affect the reported moles of CO2(g) collected—too high, too low, or unaffected? Explain Part D If a large amount of calcium sulfate [it does not form a gas with the addition of HCl(aq)] is present in the original sample, how does it affect the reported a molar volume of the CO2(g)—too high, too low, or unaffected? Explain b percent CaCO3 in the sample—too high, too low, or unaffected? Explain 182 A Carbonate Analysis; Molar Volume of Carbon Dioxide exp14.qxd 9/1/10 3:42 PM Page 183 Experiment 14 Molar Mass of a Solid A thermometer is secured with a thermometer clamp to guard against breakage • To observe and measure the effect of a solute on the freezing point of a solvent • To determine the molar mass (molecular weight) of a nonvolatile, nonelectrolyte solute Objectives The following techniques are used in the Experimental Procedure: Techniques A pure liquid, such as water or ethanol, has characteristic physical properties: the melting point, boiling point, density, vapor pressure, viscosity, surface tension, and additional data listed in handbooks of chemistry The addition of a soluble solute to the liquid forms a homogeneous mixture called a solution The solvent of the solution assumes physical properties that are no longer de nite but dependent on the amount of solute added The vapor pressure of the solvent decreases, the freezing point of the solvent decreases, the boiling point of the solvent increases, and the osmotic pressure of the solvent increases The degree of the change depends on the number of solute particles that have dissolved, not on the chemical identity of the solute These four physical properties that depend on the number of solute particles dissolved in a solvent are called colligative properties For example, one mole of glucose or urea (neither of which dissociates in water) lowers the freezing point of one kilogram of water by 1.86ЊC; whereas one mole of sodium chloride lowers the freezing point of one kilogram of water by nearly twice that amount (ϳ3.72ЊC) because, when dissolved in water, it dissociates into Naϩ and ClϪ providing twice as many moles of solute particles per mole of solute as glucose or urea When freezing ice cream at home, a salt–ice water mixture provides a lower temperature bath than an ice/water mixture alone Antifreeze (ethylene glycol, Figure 14.1) added to the cooling system of an automobile reduces the probability of freeze-up in the winter and boiling over in the summer because the antifreeze/water solution has a lower freezing point and a higher boiling point than pure water These changes in the properties of pure water that result from the presence of a nonvolatile solute are portrayed by the phase diagram in Figure 14.2, page 184, a plot of vapor pressure versus temperature The solid lines refer to the equilibrium conditions between the respective phases for pure water; the dashed lines represent the same conditions for an aqueous solution Introduction Figure 14.1 Ethylene glycol is a major component of most antifreeze solutions Colligative properties: properties of a solvent that result from the presence of the number of solute particles in the solution and not their chemical composition Nonvolatile solute: a solute that does not have a measurable vapor pressure Experiment 14 183 exp14.qxd 9/1/10 3:42 PM Page 184 Figure 14.2 Phase diagram (not shown to scale) for water (—) and for an aqueous solution (–·–·–) Vapor pressure: pressure exerted by a vapor when the vapor is in a state of dynamic equilibrium with its liquid Boiling point: the temperature at which the vapor pressure of a liquid equals atmospheric pressure Freezing point: the temperature at which the liquid and solid phases of a substance coexist The vapor pressure of water is 760 torr at its boiling point of 100ЊC When a nonvolatile solute dissolves in water to form a solution, solute molecules occupy a part of the surface area This inhibits movement of some water molecules into the vapor state, causing a vapor pressure lowering of the water (⌬v.p in Figure 14.2), lower than 760 torr With the vapor pressure less than 760 torr, the solution (more speci cally, the water in the solution) no longer boils at 100ЊC For the solution to boil, the vapor pressure must be increased to 760 torr; boiling can resume only if the temperature is increased above 100ЊC This boiling point elevation (⌬Tb in Figure 14.2) of the water is due to the presence of the solute A solute added to water also affects its freezing point The normal freezing point of water is 0ЊC, but in the presence of a solute, the temperature must be lowered below 0ЊC before freezing occurs (the energy of the water molecules must be lowered to increase the magnitude of the intermolecular forces so that the water molecules “stick” together to form a solid); this is called a freezing point depression of the water (⌬Tf in Figure 14.2) The changes in the freezing point, ⌬Tf , and the boiling point, ⌬Tb, are directly proportional to the molality, m, of the solute in solution The proportionality is a constant, characteristic of the actual solvent For water, the freezing point constant, kf , is 1.86ЊC•kg/mol, and the boiling point constant, kb, is 0.512ЊC•kg/mol ⌬Tf ϭ ͉Tf, solvent Ϫ Tf, solution ͉ ϭ kf m (14.1) ⌬Tb ϭ ͉Tb, solvent Ϫ Tb, solution ͉ ϭ kbm (14.2) In equations 14.1 and 14.2, T f represents the freezing point and Tb represents the boiling point of the respective system ͉Tf, solvent Ϫ Tf, solution͉ represents the absolute temperature difference in the freezing point change Molality is de ned as molality, m ϭ Cooling curve: a data plot of temperature versus time showing the rate of cooling of a substance before, during, and after its phase changes 184 Molar Mass of a Solid mol solute (mass/molar mass) ϭ kg solvent kg solvent (14.3) k f and kb values for various solvents are listed in Table 14.1 In this experiment, the freezing points of a selected pure solvent and of a solute– solvent mixture are measured The freezing point lowering (difference), the k f data from Table 14.1 for the solvent, and equations 14.1 and 14.3 are used to calculate the moles of solute dissolved in solution and, from its measured mass, the molar mass of the solute The freezing points of the solvent and the solution are obtained from a cooling curve—a plot of temperature versus time An ideal plot of the data appears in Figure 14.3 The cooling curve for a pure solvent reaches a plateau at its freezing point: exp14.qxd 9/1/10 3:42 PM Page 185 Table 14.1 Molal Freezing Point and Boiling Point Constants for Several Solvents Freezing Point Substance (ЊC) H2O Cyclohexane Naphthalene Camphor Acetic acid t-Butanol 0.0 — 80.2 179 17 25.5 ЊC•kg kf mol ΂ 1.86 20.0 6.9 39.7 3.90 9.1 ΃ Boiling Point (ЊC) 100.0 80.7 — — 118.2 — Њ ΂ C•kg mol ΃ kb 0.512 2.69 — — 2.93 — Extrapolation of the plateau to the temperature axis determines its freezing point The cooling curve for the solution does not reach a plateau but continues to decrease slowly as the solvent freezes out of solution Its freezing point is determined at the intersection of two straight lines drawn through the data points above and below the freezing point (Figure 14.3) Figure 14.3 Cooling curves for a solvent and solution Procedure Overview: Cyclohexane is the solvent selected for this experiment although other solvents may be just as effective for the determination of the molar mass of a solute Another solvent1 may be used at the discretion of the laboratory instructor Consult with your instructor The freezing points of cyclohexane and a cyclohexane solution are determined from plots of temperature versus time The mass of the solute is measured before it is dissolved in a known mass of cyclohexane Obtain about 15 mL of cyclohexane You’ll use the cyclohexane throughout the experiment Your laboratory instructor will issue you about g of unknown solute Record the unknown number of the solute on the Report Sheet The cooling curve to be plotted in Part A.4 can be established by using a thermal probe that is connected directly to either a calculator or computer with the appropriate software If this thermal sensing/recording apparatus is available in the laboratory, consult with your instructor for its use and adaptation to the experiment The probe merely replaces the glass or digital thermometer in Figure 14.4, page 186 Experimental Procedure t-Butanol is a suitable substitute for cyclohexane in this experiment Experiment 14 185 exp14.qxd 9/1/10 3:42 PM Page 186 Prepare the ice–water bath Assemble the apparatus shown in Figure 14.4 A 400-mL beaker is placed inside a 600-mL beaker, the latter being an outside insulating beaker You may want to place a paper towel between the beakers to further insulate the ice–water bath Place about 300 mL of an ice–water slurry into the 400-mL beaker.2 Obtain a digital or glass thermometer, mount it with a thermometer clamp to the ring stand, and position the thermometer in the test tube (Caution: If the thermometer is a glass thermometer, handle the thermometer carefully If the thermometer is accidentally broken, notify your instructor immediately.) Prepare the cyclohexane Determine the mass (Ϯ0.01 g)3 of a clean, dry 200-mm test tube in a 250-mL beaker (Figure 14.5) Add approximately 12 mL of cyclohexane (Caution: Cyclohexane is ammable—keep away from ames; cyclohexane is a mucous irritant—do not inhale) to the test tube Place the test tube containing the cyclohexane into the ice–water bath (Figure 14.4) Secure the test tube with a utility clamp Insert the thermometer probe and a wire stirrer into the test tube Secure the thermometer so that the thermometer bulb or thermal sensor is completely submerged into the cyclohexane Record data for the freezing point of cyclohexane While stirring with the wire stirrer, record the temperature at timed intervals (15 or 30 seconds) on the second page of the Report Sheet The temperature remains virtually constant at the freezing point until the solidi cation is complete Continue collecting data until the temperature begins to drop again Plot the data On linear graph paper or by using appropriate software, plot the temperature (ЊC, vertical axis) versus time (sec, horizontal axis) to obtain the cooling curve for cyclohexane Have your instructor approve your graph A Freezing Point of Cyclohexane (Solvent) A modern digital thermometer Appendix C 110° glass or digital thermometer Stirring wire 110 glass or digital thermometer 200-mm test tube Ice bath Ice bath Cyclohexane (and solution) Figure 14.4 Freezing point apparatus Rock salt may be added to further lower the temperature of the ice–water bath Use a balance with Ϯ0.001 g sensitivity, if available 186 Molar Mass of a Solid ... Common Laboratory Desk Equipment Checklist First Term No 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Second Term Third Term Quantity Size Item In Out In Out In Out 1 1 1 1 1 1 2 1 1 10 -mL 50-mL... 9 /1/ 10 4:37 PM Page i Laboratory Manual for Principles of General Chemistry This page intentionally left blank ffirs.qxd 9 /1/ 10 4:37 PM Page iii Laboratory Manual for Principles of General Chemistry. .. case of an accident, general laboratory rules, and work ethics in the laboratory are presented vi Laboratory Manual for Principles of General Chemistry fpref.qxd 9/3 /10 1: 40 PM Page vii • Laboratory