CHEMISTRY - Chem21Labs · Experiment 7 Acid–Base Titration ... Experiment 9 Using Redox Chemistry...

Laboratory Manual

G e n e r a l

Department of ChemistryUniversity of Kentucky

Dr. April N. FrenchDr. Allison SoultDr. M. Meral SavasDr. François BothaDr. Carolyn BrockMr. Charles GriffithMs. Darla HoodDr. Robert KiserDr. Penny O’ConnorDr. William PlucknettDr. Donald SandsDr. Diane VanceDr. William Wagner

CHEMISTRY

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iii

Table of Contents

Introduction to the Laboratory ............................................................................... v

Chapter 1Laboratory Safety ..................................................................................................... 1

Chapter 2Laboratory Notebooks and Reports ....................................................................... 11

Chapter 3Techniques for General Chemistry Lab ................................................................. 25

Chapter 4Using MeasureNet and Probes ............................................................................... 33

Experiment 1Scientific Writing and Integrity ............................................................................. 43

Experiment 2Starting a New Laboratory Position ....................................................................... 49

Experiment 3Introduction to Data Analysis ............................................................................... 57

Experiment 4Quantifying the Composition of Limestone ......................................................... 65

Experiment 5Synthesis of Aspirin ............................................................................................... 73

Experiment 6Ten Test Tube Mystery ........................................................................................... 79

Experiment 7Acid–Base Titration ................................................................................................ 85

Experiment 8Enthalpy of Reaction ............................................................................................. 93

Experiment 9Using Redox Chemistry and Color to Identify DNA ............................................. 99

Appendices A Laboratory Equipment ........................................................................... 107 B Units and Constants .............................................................................. 109 C Ions ......................................................................................................... 113 D Solubility ................................................................................................ 115 E Standard Deviation ................................................................................ 117

iv

General Chemistry

v

Tell me and I forget. Teach me and I remember. Involve me and I learn.—Benjamin Franklin

Welcome to General Chemistry Lab. A laboratory experience can enhance your knowl-edge and understanding of a subject by giving you hands-on experience applying the concepts and principles which you have learned or are learning in your General Chem-istry lecture course. A laboratory course is different than a lecture course because it allows you to be involved in what is happening. I hope that you take full advantage of the opportunities available in this class to witness chemical principles in action, rather than seeing photos of, hearing someone talk about, or reading about them.

This laboratory manual contains information about all the experiments we’ll be doing as well as reference information about safety, lab reports, conversion factors, data on various elements and compounds, and more. Additional information is also available on the Blackboard Web site for this course (see the syllabus for information on accessing the course Web site). You are strongly encouraged to read all the information in the lab manual as well as the information posted on the Web site. Reviewing this information is critical to your success in the course. One of the most important things you can do in this course is READ.

You cannot escape the responsibility of tomorrow by evading it today.—Abraham Lincoln

There are many components to your grade for this course, which are outlined in the course syllabus. You are responsible for reading the syllabus and adhering to all as-signment due dates and policies. You should read the syllabus carefully and direct any questions you have to your Teaching Assistant and/or to the Lab Supervisor. It is in your best interest to read the syllabus and get any questions answered sooner, rather than later, so that you are not penalized for missing a due date or for misunderstanding a course policy (i.e., mandatory attendance).

Introduction to the Laboratory

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General Chemistry

It is important that you take an active role in your learn-ing by seeking help, asking questions, and participating in this course. Think about taking a class like a trip to the grocery store. You don’t go to the grocery and expect someone to know exactly what you need and bring it to you. You have to figure out what you need and go looking for it. Maybe it’s a store you’ve never been in before and you have to walk around a little to find where the cereal aisle is or the frozen foods are. As you walk through the store, you may be offered help by clerks, but you’re sure you can do it alone. Then when the clerks disappear, you realize you do need help! Maybe you’ve found the cereal aisle, but you can’t find the Super Sugar Rings that you absolutely must have in order to func-tion. Now, you’re faced with some choices:

1. Keep looking in the same place you’ve been look-ing because you’re positive you can do this on your own, after all if you’re able to get to the grocery store, then you should be able to find the Super Sugar Rings.

2. Give up because if you can’t find them, they must not be there and you’ll have to do without.

3. Go find someone who can help you and ask them where the Super Sugar Rings are and find out that because the Super Sugar Rings are on sale this week, they are on the end cap of the soda aisle instead of being in the cereal aisle.

The same thing applies in this course, there are people to help you along the way but you have to find them and bring your questions to them so they know exactly what you need and can help you.

Electronic ResourcesThere is additional information on experiments through Blackboard including tutorials, videos (i.e., Using a Buret, Dispensing Liquids and Solids), and sample calculations. Some of the information will be required viewing, while other resources are there to help you when you need it.

Answers to many questions can be found in the FAQ on Blackboard.

There are many people involved in this course who each have their own important role.

Lab Supervisor: The job of the lab supervisor is to supervise the teaching assistants, write quizzes and ex-ams, help students, resolve student–TA problems, assign final course grades, and other administrative tasks. The lab supervisor has regularly scheduled office hours, but is generally available at other times.

Storekeeper: A member of the chemistry stockroom staff works with the General Chemistry laboratory courses by preparing chemical and unknown solutions, setting up necessary supplies and reagents, and helping students replace missing and/or broken equipment.

Teaching Assistant: TAs are responsible for the direct supervision of students in the laboratory, helping stu-dents, grading lab reports, and giving input on students’ course grades.

Student: Your job is to come to class prepared to do the assigned experiment in the allotted time, work with other students on experiments, follow safety rules, keep lab spaces clean, submit all assignments on time, and to READ. You should read the syllabus, the lab manual, the Web site, and any other material that is given to you so that you know exactly what to expect in this course.

The Director of General Chemistry oversees the ad-ministration of this course and can discuss problems or concerns that a student does not feel is resolved by discussing it with their TA and/or the Lab Supervisor.

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Laboratory Safety

C h a p t e r 1

By its nature the chemical laboratory can be a dangerous place to work. The improper use of chemicals and equipment can cause severe and/or permanent damage to your body. And you are not the only one at risk. Your actions can affect your coworkers, those who follow, and the environment. One of the more important aspects of your chemistry lab experience will be learning how to perform experiments as safely as is humanly possible. You will learn how to protect yourself and others from the hazardous conditions created by your experimentation.

1-1 Safe Laboratory PracticesIt is common knowledge that doing chemistry is a hazardous activity. But so is driving a car or cooking. As with these other activities, the trick to safely working in a chemistry lab is to learn safe practices and develop safe working habits. This course is designed to teach safe lab practices and to help you develop habits that will lead to efficient, ef-fective, and safe experimentation.

When performed correctly, the experiments presented in this course are safe. But this is a teaching lab. Mistakes will be made. Misinterpretation of the instructions or use of the wrong chemicals can result in a serious accident. And no matter how careful you are, the student working next to you may be doing something to endanger your health that you are helpless to prevent. No matter how much faith you have in your ability to work safely in the laboratory it is foolish to believe that an accident can’t happen to you.

The safety rules for working in this lab are designed with this idea in mind. If you faith-fully adhere to these rules, and to your instructor’s precautions, you will find working in the chemical laboratory to be no more dangerous than working in a kitchen or driving a car.

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C h a p t e r 1 • Laboratory Safety

Chapter

1

Keep in mind that safety rules don’t exist just to protect you and your lab mates. They are also intended to help instill safe working habits. Because habits are developed by repetition, it is expected that you will adhere to these rules at all times, regardless of the level of danger posed by any particular experiment.

1-2 Safety IssuesEye ProtectionYour eyes are quite possibly the most fragile parts of your body. They are certainly very important and im-possible to replace. And they face many dangers in a chemical lab. Proper protection of the eyes is mandator y in a chemical lab.

While explosions pose the most dramatic danger to your eyes, they are not very common in chemistry labs. The greatest danger is from splashed chemicals and fumes. Safety glasses provide protection against explosions, but are not effective against splashes and fumes. Goggles with perforations are better, but still not adequate to handle most chemical fumes. Only vented goggles or full safety shields are considered adequate to protect you from splashed chemicals, flying glass,

and noxious fumes.

Figure C1.1. Vented goggles.

Chemistry labs are equipped with eyewash stations to provide first aid in the event some foreign body or chemical enters the eye. You need to know the location and proper operation of the nearest eyewash to your work space. Should you get a chemical in your eye, or should chemical vapors cause your eyes to water, immediately wash your eyes with lots of water. To be effective, eye washing must be continuous for at least 15 minutes.

Figure C1.2. Eyewash fountain.

There is no consensus on the danger related to wear-ing contact lenses in the lab. To date, there is no data that shows either greater or lesser risk from wearing contacts. On the one hand, fumes that get in the eye will probably get under the lens. In this event the lens will aggravate any exposure. On the other hand, the contact lens will protect the cornea from direct chemi-cal or physical contact.

ClothingYou should think about what you will wear to lab. Many fabrics, such as nylon and polyester, react with com-mon lab chemicals and burn well. Cotton clothing is the best. To protect yourself against splashed or spilled chemicals you should also cover as much of your skin as is practical. That means a long sleeve shirt and long pants. Finally, as a first line of defense, a lab coat or apron can’t be beat.

Don’t forget to consider what shoes to wear. Because broken glass and spilled chemicals are common to the lab, closed-toed, non-absorbent shoes are a must. Con-sider what would happen if you were wearing canvas sneakers and socks and spilled an acid on your shoe. It would soak through the shoe and through the sock to your foot. In the time it would take you to get the shoe and sock off significant damage would be done.

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Figure C1.3. Lab coat and apron.

Chemistry labs are equipped with safety showers to provide first aid should you spill any chemical on your skin or clothing. You need to know the location and proper operation of the safety showers in your lab. Im-mediately wash the affected area with lots of water and continue the washing for 15 minutes.

A note on chemical contact.Chemical burns can be just as nasty as heat burns and often cause no pain until after damage is done. Any chemical contact with skin should be treated as a potential chemical burn. When this happens, contact your instructor.

Figure C1.4. A lab safety station.

GlovesHands present a special case. When we manipulate glass-ware and other laboratory equipment, we depend on our sense of touch to direct our activities. Gloves limit our sense of touch and, therefore, our dexterity. Using gloves increases the chance of an accident. In addition, the skin on hands is tougher than other skin. It comes with its own protective layer of callouses. The decision to use gloves must balance the added protection they provide for the hands against the loss in dexterity.

There are two dangers from chemical contact with skin:

1. destruction of tissue (chemical burns) and 2. poisoning due to absorption through the skin. When you will be working with a sufficiently dangerous chemical, you will be instructed to wear gloves.

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ReagentsThe place where reagents are stored is known as the reagent bench. It will have most of the non-danger-ous chemicals and other supplies that you will need to perform your experiments. More dangerous chemicals are stored in a hood. The proper procedure for obtain-ing a reagent is to take an appropriate container to the bench and take only what you need. Transporting a large container of any chemical can be hazardous and is to be avoided.

Figure C1.5. A reagent bench.

When using reagent bottles you must be observant for spills. One common cause of chemical burns in a teaching lab is reagent on the outside of the bottle. It is easy to slop reagent down the outside of the bottle. If you do so, make sure you clean it up. And watch for wet bottles!

When using reagent bottles you must also avoid con-tamination. You must develop habits that will minimize the possibility of contamination.

• NEVER set the cap to the reagent bottle down. Hold it between the second and third fingers of one hand.

• NEVER insert objects (including pipets) into reagent bottles. Instead, transfer some of the reagent to a clean beaker and pipet from this container.

• NEVER return unused reagent to the reagent bottle. Dispose of all unused reagent as chemical waste.

LabelsCheck the label carefully before you use a reagent. Use of the wrong reagent will ruin your experiment and could result in a serious accident. You also need to make sure you label everything you make and use in the lab. Many accidents result from assumptions made about unlabeled containers.

PrecautionsPrior to each experiment your instructor will tell you how to properly use chemicals and equipment. You are expected to follow these instructions.

Waste DisposalYou will need to become familiar with the various kinds of waste generated in a chemistry lab and the proper protocol for disposing of each. The kinds of waste are:

• Solid chemical waste.

• Glass waste.

• Garbage (stuff that can go in the garbage can: no glass, no chemicals).

• Liquid organic waste.

• Acidic water solutions.

• Basic water solutions.

• Heavy metal water solutions.

• Drain water. (Only neutral water solutions that do not contain heavy metals or organics can be poured down the drain. No solids!)

Figure C1.6. Chemical waste hood.

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Clean UpAt the end of the class you are expected to turn off all water and gas jets, return all borrowed items, and put all of your equipment back into your locker and lock it. You also must leave a clean work bench for the student that follows.

AccidentsShould an accident occur, it is important to notify the instructor immediately. Even something as seemingly innocuous as cutting yourself on a broken piece of glass could become very nasty if that glass were contaminated with a dangerous chemical. Let your instructor help to judge the severity of any incident.

EvaluationThe most basic objective of a chemistry lab course is to teach you how to safely work in a chemical lab. Your grade will depend, in part, on how well you demon-strate your knowledge of safe laboratory practices. You should expect to see the material presented here on the exams you take. In addition, your instructor’s evalua-tion of your lab performance will be based, in part, on your adherence to safe laboratory practices and the lab rules. Finally, should you demonstrate a lack of regard for safety rules, or laboratory safety in general, you will be prohibited from working in the lab.

1-3 Safety Assignment1. When are safety goggles to be worn in the lab? Who

must wear them?

2. What function do the hoods serve? When must you use them?

3. Why must shoes be worn in the lab? Why are san-dals prohibited?

4. Your neighbor is carrying a bottle of concentrated nitric acid back to the lab bench. He trips and drops the bottle which breaks and splatters its contents all over your legs. What do you do? What did your neighbor do wrong?

5. Make a diagram of your lab room. On this diagram indicate the location of the following items:a. your workspaceb. the hoodsc. the nearest safety showerd. the nearest eyewash statione. the nearest fire extinguisherf. the first-aid boxg. the exitsh. the reagent bench

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Chapter

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Safety in a Chemistry LaboratoryOne of the most important aspects of any chemistry lab is safety and this course is no exception. All students are required to read the safety information in the lab manual, watch a safety video, sign and submit a copy of this form, and pass a safety quiz in order to participate in this course. While some of this may seem repetitious, it illustrates the importance we place on your safety and the safety of those around you. Violation of any safety rules will not be tolerated. Failure to remedy an unsafe situation will result in students being asked to leave the laboratory. Missing an experiment due to a student’s failure to follow safety rules will not be considered an excused absence. Students should read and understand the rules listed below.

1. Your eyes are the most vulnerable part of your body to the dangers of working in a chemistry lab. You are required to wear protective eyewear whenever you or anyone else in the lab is transporting or using chemicals and/or glassware. Only chemical splash goggles which meet the current safety stan-dards are permitted. The cost of goggles is included in the cost of Chem21. When you have paid for Chem21 and submitted your access code online, you will receive your goggles from your TA during Experiment 1. You will be required to bring and wear your goggles to participate in lab. Sunglasses and prescription glasses are not acceptable forms of eye protection. Other types of goggles must be approved by the Laboratory Supervisor.

2. Appropriate clothing must be worn, including long pants or skirts, shoes with closed toes (shoes which cover your feet completely are preferable), and shirts which meet the top of your pants or skirt (i.e., no bare stomachs or backs). Students not wearing appropriate clothing will be asked to leave the lab immediately.

3. No smoking, drinking, or eating (including gum) at any time in the laboratory. All bottles, cups, and food must be left outside the lab or placed into your closed backpack, bag, or pocket. Food or beverage containers must be disposed of prior to entering the lab and cannot go into the trash cans in the lab.

4. Never work alone in the laboratory. Students must be supervised by a TA or the Lab Supervisor during all experiments.

5. Never leave an experiment or running equipment unattended. Surprises are usually not a good thing in a chemistry lab.

6. Only do the assigned experiment. Additional ex-periments are not allowed to ensure the safety of you and those around you.

7. Do not remove chemicals, equipment, or glassware from the laboratory. Any student alleged to have removed any of the items listed above from the laboratory will be reported to the police. Any stu-dent caught removing any of the items listed above will be prosecuted. If a student is convicted, the case will be turned over to the Dean of Students and the Department of Chemistry may recommend that the Dean of Students seek the harshest of University sanctions, which includes expulsion.

8. Do not wear gloves out of the laboratory, regardless of whether you have started working in the lab or not.

9. Know the location of all safety equipment in the room as well as the location of the nearest exit from the room and building.

10. If there is an accident, no matter how minor, con-tact your TA immediately.

11. Double-check all labels before using them in an experiment to make sure it is the correct chemical and concentration. Substituting another chemi-cal or concentration could cause unexpected and dangerous consequences.

12. Discard broken, cracked, or chipped glassware immediately in the appropriate containers. Do not place glassware in the trash cans under any circumstances. Broken items can be replaced by contacting the stockroom.

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13. Tilt test tubes while heating, being careful not to point them at anyone.

14. Wipe down your workspace with a wet towel be-fore leaving the laboratory to ensure that other students are not unknowingly placed in contact with chemicals.

15. If you have any medical condition (allergies, preg-nancy, etc.) which may affect your performance in the lab, please notify the Lab Supervisor immedi-ately so that any safety issues can be addressed.

16. Dispose of waste in the appropriate container(s). When in doubt, ASK!

17. If the fire alarm goes off, turn off your equipment, collect your belongings, and proceed to the nearest exit. All labs are to meet their TA on the hill where the TA will take attendance. The Lab Supervisor will make all decisions regarding the completion of the lab on a case-by-case basis.

By signing below, I indicate that I have read and understand the safety information provided to me in the lab manual, on the safety video, and by my TA. I also realize that it is my responsibility to follow all safety rules and that I will be removed from the laboratory for repeated violations of these rules.

Initial by each of the following statements to indicate that you have read them.

• I understand the policies of this course as outlined in the syllabus.

• I have seen the list of due dates for all assignments in the syllabus.

Name (print) _______________________________________________________________________________________

Signature __________________________________________________________________________________________

Date Section TA

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Chapter

1

One of the most important aspects of any chemistry lab is safety and this course is no exception. All students are required to read the safety information in the lab manual, watch a safety video, sign and submit a copy of this form, and pass a safety quiz in order to participate in this course. While some of this may seem repetitious, it illustrates the importance we place on your safety and the safety of those around you. Violation of any safety rules will not be tolerated. Failure to remedy an unsafe situation will result in students being asked to leave the laboratory. Missing an experiment due to a student’s failure to follow safety rules will not be considered an excused absence. Students should read and understand the rules listed below.

1. Your eyes are the most vulnerable part of your body to the dangers of working in a chemistry lab. You are required to wear protective eyewear whenever you or anyone else in the lab is transporting or using chemicals and/or glassware. Only chemical splash goggles which meet the current safety stan-dards are permitted. The cost of goggles is included in the cost of Chem21. When you have paid for Chem21 and submitted your access code online, you will receive your goggles from your TA during Experiment 1. You will be required to bring and wear your goggles to participate in lab. Sunglasses and prescription glasses are not acceptable forms of eye protection. Other types of goggles must be approved by the Laboratory Supervisor.

2. Appropriate clothing must be worn, including long pants or skirts, shoes with closed toes (shoes which cover your feet completely are preferable), and shirts which meet the top of your pants or skirt (i.e., no bare stomachs or backs). Students not wearing appropriate clothing will be asked to leave the lab immediately.

3. No smoking, drinking, or eating (including gum) at any time in the laboratory. All bottles, cups, and food must be left outside the lab or placed into your closed backpack, bag, or pocket. Food or beverage containers must be disposed of prior to entering the lab and cannot go into the trash cans in the lab.

4. Never work alone in the laboratory. Students must be supervised by a TA or the Lab Supervisor during all experiments.

5. Never leave an experiment or running equipment unattended. Surprises are usually not a good thing in a chemistry lab.

6. Only do the assigned experiment. Additional ex-periments are not allowed to ensure the safety of you and those around you.

7. Do not remove chemicals, equipment, or glassware from the laboratory. Any student alleged to have removed any of the items listed above from the laboratory will be reported to the police. Any stu-dent caught removing any of the items listed above will be prosecuted. If a student is convicted, the case will be turned over to the Dean of Students and the Department of Chemistry may recommend that the Dean of Students seek the harshest of University sanctions, which includes expulsion.

8. Do not wear gloves out of the laboratory, regardless of whether you have started working in the lab or not.

9. Know the location of all safety equipment in the room as well as the location of the nearest exit from the room and building.

10. If there is an accident, no matter how minor, con-tact your TA immediately.

11. Double-check all labels before using them in an experiment to make sure it is the correct chemical and concentration. Substituting another chemi-cal or concentration could cause unexpected and dangerous consequences.

12. Discard broken, cracked, or chipped glassware immediately in the appropriate containers. Do not place glassware in the trash cans under any circumstances. Broken items can be replaced by contacting the stockroom.

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Chapter

1

13. Tilt test tubes while heating, being careful not to point them at anyone.

14. Wipe down your workspace with a wet towel before leaving the laboratory to ensure that other students are not unknowingly placed in contact with chemicals.

15. If you have any medical condition (allergies, preg-nancy, etc.) which may affect your performance in the lab, please notify the Lab Supervisor immedi-ately so that any safety issues can be addressed.

16. Dispose of waste in the appropriate container(s). When in doubt, ASK!

17. If the fire alarm goes off, turn off your equipment, collect your belongings, and proceed to the nearest exit. All labs are to meet their TA on the hill where the TA will take attendance. The Lab Supervisor will make all decisions regarding the completion of the lab on a case-by-case basis.

By signing below, I indicate that I have read and understand the safety information provided to me in the lab manual, on the safety video, and by my TA. I also realize that it is my responsibility to follow all safety rules and that I will be removed from the laboratory for repeated violations of these rules.

Initial by each of the following statements to indicate that you have read them.

• I understand the policies of this course as outlined in the syllabus.

• I have seen the list of due dates for all assignments in the syllabus.

Name (print) _______________________________________________________________________________________

Signature __________________________________________________________________________________________

Date Section TA

11

Laboratory Notebooks and Reports

C h a p t e r

2

During an experiment, students collect data and make observations about an experiment. This information should be recorded in your lab notebook and then used to complete the assignment(s) in the schedule. The lab notebook is used as an original record of your data, while a lab report is the formal presentation and discussion of the experiment and your results. The lab report should be typed and contain no errors, but the lab notebook will be handwritten and may contain errors.

Laboratory NotebooksWhy are lab notebooks so important? A lab notebook is the original record of your data and should contain any information that you might need when writing your lab report. If there is something you are not sure you will need, write it down anyway. If you have it and don’t need it, it’s not a problem. If you need it and don’t have it, you have a problem.

If you plan a career that involves research, a lab notebook is very important. U.S. Patents are decided by the date of invention, not the date of application. Failing to accurately document and date your findings means that the patent application could be denied which could result in the loss of substantial amounts of fame and fortune for you and/or your employer. If you are planning a career in a medical field, it is imperative that you accurately record all patient information. Failure to document symptoms and test results could result in a misdiagnosis which could lead to being sued for medical malpractice.

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C h a p t e r 2 • Laboratory Notebooks and Reports

Chapter

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Before Lab

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After Lab

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The lab notebook (purchased separately) should be used to record the following information:

• Basic information

• Name

• Experiment number and name

• Date (all pages should be used in sequential order)

• Name of lab partner

• Course and section number

• Signature of student

• Signature of TA

• Procedure planned and carried out in lab. Do not print out the lab manual for lab.

• List of any changes to the procedure published in the lab manual.

• This should include changes announced in class, on Blackboard, etc.

• Qualitative data (i.e., after addition of HCl, a lemon yellow precipitate formed).

• Quantitative data (i.e., mass of the metal cube—2.5434 g, 2.3425 g, 2.4344 g).

• Note the description of the item as well as the units.

• File names of any data collected and saved electronically.

• Include some type of identifying information for all electronic data files such as the initial or final temperature, approximate equivalence point, etc.

• All calculations, making sure to show all steps. If you make an error, you, a TA, or Lab Supervisor can use this information to find the error.

When writing information in your lab notebook, you should always do the following:

• Always write in blue or black ink.

• Always write your data directly in your lab notebook.

• Do not write the information on a separate piece of paper and transfer it.

• It is okay if the lab notebook is not perfect or contains errors.

• Do not record data in the middle of the procedure.

• Never remove pages from your lab notebook. The pages are numbered sequentially and should remain intact even if you use additional pages for calcula-tions or other notes.

• Mark out any errors with a single line so that the original information is still legible but the line clearly indicates that it is incorrect.

• Organize data in tables when collecting multiple values.

• Label all values (i.e., volume of water used).

• Do not have “orphaned” numbers. All values should have labels and units.

• Include units for all numbers.

• Record all qualitative observations.

• Record all unknown numbers/letters.

• Record concentrations of all solutions used.

At the end of each lab session, have your TA sign your lab notebook and then turn in the copy of your results to them. This allows your TA to verify data presented in your report and identify any recurring problems in the experiment. The data in your report should match that in your lab notebook exactly. Any discrepancies should be explained prior to submitting the report.

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1 Some information and descriptions of categories for the grade sheet come from http://labwrite.ncsu.edu, a project funded by the National Science Foundation and available to students everywhere.

Assignments1

Part of your grade in this course will be based upon the assignments submitted for each experiment. There are three main types of assignments which you will complete in this course:

• Chem21: Online data analysis which will be com-pleted for each experiment.

• Lab Report: Students will complete either a section or a full report for most experiments. See the course schedule for a description of what is due. All final versions of reports or portions of them are to be submitted electronically on Blackboard.

• Peer Review: Your TA and two of your classmates will use a feedback form to help you improve your lab report before you submit the final copy on Blackboard.

• Worksheet: A longer assignment on Chem21 labs, generally completed on weeks you don’t submit a lab report, is worth more points than normal Chem21 assignments.

See the syllabus for an explanation of how each assign-ment contributes to your final course grade.

Laboratory Reports1

The purpose of a lab report is to explain the theory behind the experiment, present the results, and discuss how the results relate to the theory. Someone who has not done the experiment or even read the experiment in the lab manual should be able to read your lab report and understand what you were trying to do, see the summary of your data, and understand the results of your experiment. Lab reports allow you the opportu-nity to interpret your data and relate it (or not) to the theory behind the experiment. While it is much easier to explain data that agrees with the theory, you will prob-ably find that in one or more experiments, you might get an unexpected result. Do not change your data or use someone else’s data just because your numbers “look bad.” What is more important is that you either see potential sources of error that could have led to the results and/or that you try to explain the results that disagree with the underlying theory.

We understand that some students have never written a lab report before or have written reports following a different format. If you are in this situation, you are not alone. All students should follow the guidelines presented here to write their reports and contact their TA for help, if needed.

Do NOT copy another student’s work or from the lab manual when writing your lab report. Do not use someone else’s report as a “guide” or a “template.” Students may discuss content but lab reports (including text, tables, equa-tions, graphs, etc.) should be written indepen-dently of other students, their lab reports and the lab manual. Do not resubmit any part of a report you have turned in before.

Lab reports are submitted electronically and copies of all reports for both the current and previous semesters are kept on file. Reports submitted electronically are compared to all reports submitted in both previous and current semesters. If you copy from another student or the lab manual, you will get caught. Using someone else’s work without giving them the appropriate credit is plagiarism, which is an academic offense. Academic offenses are taken very seriously by the Department of Chemistry and the University of Kentucky.

Penalties for academic offenses can be as severe as sus-pension, dismissal, or expulsion from the University. The minimum penalty in general chemistry lab courses is a zero on the assignment and a reduction of the final course grade by one letter grade. If you have questions about academic offenses or plagiarism, please contact your TA or the lab supervisor; review the relevant rules of the University Senate (Rule 6.3); or contact the Writ-ing Center.

Each part of the lab report will be discussed in more detail, but the following are some general tips on writ-ing lab reports:

• Reports must be completely typed.

• Save early, save often.

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• Computers lock up and break down. Save your work and back up your files.

• Microsoft Word is preferred when writing your reports.

• As the lab manual went to press, Microsoft Office is available free to students at http://download.uky.edu. Help with the download and/or installation is available from the IT Customer Service Center in McVey Hall.

• Microsoft Office is installed on all campus computers.

• Students should not use Microsoft Works as it does not handle images well and frequently creates files larger than 10 MB which will not be accepted on Blackboard.

• Mac users should see the FAQ for additional information.

• Microsoft Word is also available in campus computer labs.

• If Word is not an option to write your report, you may use OpenOffice (www.openoffice.org) but you must save the file as the type “Microsoft Word 97/2000/XP.”

• Reports must be submitted electronically using the link given in the course syllabus and on Blackboard. Paper or e-mailed copies will not be accepted.

• Proofread your lab report before submitting it to check for grammatical or spelling errors.

• Do not wait until the last minute to complete your report. If you need help late at night or in the early hours of the morning before the report is due, you may not be able to get it before the report is due.

• It is always a good idea to make sure you can open any data files shortly after your lab session in case there are any problems with the file.

• If you are unable to complete the paper, it is better to take a zero than face academic of-fense charges.

• Your lab report will be graded by your TA who may have their own formatting preferences (spacing, font, graph size, etc.).

• Always separate parts of your lab reports with head-ings for each section (i.e., Results, Discussion, etc.).

• With the exception of the conclusion, the rest of the report should be written in third person.

• Instead of saying “I recorded the mass of the sample,” say “The mass of the sample was recorded.”

Lab reports will be graded electronically and an Excel spreadsheet will be returned to you via Blackboard with your grade. An example of the spreadsheet is included on page 17. This also serves as an outline for explaining the different parts of a lab report. You should receive your grade within one week of the due date of the report. If you are not receiving your grades in a timely manner, please contact the Lab Supervisor.

The point value for each item will vary with each experi-ment depending on the level of difficulty for a particular section. The values in the sample grade sheet are meant as an example. Each item is graded on a scale of 1 (excel-lent) to 0 (poor) in 0.25 point increments. This value is then multiplied by the point value to get your score for that particular section of the report. Your TA should include comments in the grade worksheet returned to you and/or in a general e-mail to all students. If you have questions about the grade on your lab report, you should see your TA first since they are the ones that graded the report. If you still have questions, contact the Lab Supervisor.

Contact your TA as soon as you have questions so that you can make the needed corrections on future lab reports. It is in your best interest to talk to your TA about your grades as questions arise. Waiting until all assign-ments have been submitted is not helpful for you.

The format for lab reports varies among different fields of science (i.e., physics, biology, chemistry) and there can be differences within one field. While the compo-nents of each may be generally the same, they may use different section titles, expect different things, or

http://download.uky.edu

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Student Name: Jane Doe Experiment #: 7

0, 0.25, 0.50, 0.75, 1.0 Poor to Excellent

Miscellaneous

Deductions for late reports, safety, etc. (use minus sign) or points for rough draft (#2 & #11 only)

Title (3)

File named correctly and in correct format 1 1.00

Header information 0.75 0.75

Describes lab content concisely, adequately, appropriately 1 1.00

Introduction (6)

Successfully establishes the scientific concept of the lab 1 2.00

Effectively presents the objectives and purpose of the lab 0.75 1.50

Includes support or reasoning for objectives, including equations and formulas 1 2.00

Methods (1)

Includes appropriate reference or enough details to replicate unpublished procedure 1 1.00

Discussion (14)

Statement of purpose/hypothesis 1 2.00

Opens with summary of relevant results 0.75 2.25

Explains if results support original purpose/hypothesis 1 3.00

Explains why the results support the original purpose/hypothesis or not 0.75 2.25

Addresses other issues important to the lab and their effect on the results 0.5 1.50

Conclusion (2)

Convincingly describes what has been learned in the lab 1 1.00

Has successfully learned what the lab is designed to teach 1 1.00

Presentation (4)

Citations and references adhere to proper format 0.75 0.75

Formatting of report is correct 1 1.00

Report is written in scientific style: clear and to the point 0.5 0.50

Grammar and spelling are correct 0.75 0.75

Points Earned 23.25

Total Possible Points 30

TA: Joe Smith Date: 10/15/2009

7_Jane Doe

SectionPoints

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2 Equation Editor is available in MS Word and OpenOffice. For help in finding, installing and/or using Equation Editor on your computer, see the information posted on Blackboard or search for more information on the Web using a search engine, such as www.google.com.

have different standards. Likewise, any lab reports you wrote in high school may be very different than what you will do in this class. The following information discusses what to do and not do for each section of your lab report. Please note that the items listed follow the grading sheet which will be used to grade your report.

TitleFile named correctly and in the correct format• Follow the format experimentnumber_lastname_

firstname.doc

• Jane Doe submitting the report for Experiment #8 would name the file 8_doe_jane.doc

• The file must be in MS Word 2003 or later format.

Header informationAbove the title, you should give some basic information including the following:

• Name

• Course and section number

• TA’s name

• Lab partner’s name

• Date

Describes lab content concisely, adequately, and appropriatelyThe title should give the reader an idea of what the report is about. A good title should:

• Be descriptive and concise.

• Be appropriate to the experiment.

• Not be too long (usually no more than one line) and not a complete sentence.

• Not be identical to the lab manual.

Introduction The purpose of the introduction is to give some back-ground and theoretical information for the experiment in order to explain what concepts or theories are appli-cable to the experiment, explain what you are trying to determine in the experiment, and why this experiment should support the theoretical concepts stated.

Successfully establishes the scientific concept of the lab• Gives all relevant theoretical and background in-

formation for the experiment.

• Explains the concepts in a logical manner.

• Discusses general concepts of experiment.

• Using the lab manual or other sources as a refer-ence is acceptable, but the use of direct quotations should be minimal.

Effectively presents the purpose/hypothesis and objectives for the lab• The purpose/hypothesis should be specific and

pertinent to the experiment.

• The purpose/hypothesis should in some way predict the outcome of the experiment based on theoreti-cal information, not on the data collected for the experiment.

• Objectives should be stated in your own words. The objectives for the lab given in the report will not be the same as those given in the lab manual and should focus on the overall goal of the lab.

Includes support or reasoning for objectives including all needed chemical equations and formulas and mathemati-cal formulas• Explain how the experiment will support the

purpose/hypothesis.

• Gives information specific to this experiment.

• Include any relevant chemical equations and/or formulas. Use Equation Editor for any mathemati-cal formulas.2

• Include any relevant mathematical formulas, defin-ing any variables, and an explanation of when the formula can be used (i.e., discuss any limitations of formula).

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MethodsThe methods section should outline the exact ex-perimental procedures followed. If the procedure is published in the lab manual, you should not rewrite the procedure, but instead reference it and make note of any changes.

When procedure is in lab manual• Include all necessary information for the source of

the procedure including page numbers and whether there are changes or not.

• Changes, including changes in equipment or ma-terials, are to be clearly explained.

• If there are no changes to the procedure in the lab manual, you should state “No changes to the published procedure.”

• Do not rewrite or quote the complete procedure from the lab manual.

• Do not include any results or data in the procedure.

When procedure is not in lab manual• Write procedure clearly so that it can be replicated

using only what is written.

• Include a list of needed chemicals, equipment, and/or materials.

• Include all steps that you planned to do and steps that were added when you actually did the experiment.

• As a rule of thumb, give enough detail so that your mom could repeat the experiment.

• Do not include how to calculate values or that you need to do a calculation.

• Cite any source used when developing your procedure.

ResultsThe results section of a report generally includes your data as well as any calculations and/or graphs. Rather than writing a results section in your report, you will complete this online at www.chem21labs.com. You will receive an e-mail with your login information after

the last day to add a class.You will need to purchase ac-cess either by buying an access code at the bookstore or directly through the Web site. Access is good for one semester. You will need this code when you log in to Chem21 to have access for the semester.

DiscussionThe discussion section is where we bring the theo-retical information (from the Introduction) and the experimental information (from the Results) together. The discussion is also where potential sources of error should be discussed. The order of information in the discussion is important. In general, the discussion should be longer than the introduction. If not, the introduction is too long and/or the discussion is too short.

Statement of purpose/hypothesis• One or two sentences restating the original pur-

pose/hypothesis of the experiment based on the theoretical and background information.

• Do not change your purpose/hypothesis because it does not match your results.

• Place this at the very beginning of the discussion section.

Summary of relevant results• Include this information immediately after your

restatement of purpose/hypothesis.

• Gives summary of key results including, but not limited to, average values, percent error, and/or standard deviation.

• Make sure all numerical values have the correct units and are correctly formatted (i.e., for standard deviation: 36.1 ± 1.1 g).

• Do not repeat all of the data reported in the results section.

Explains if results support original purpose/hypothesis of experiment• State whether or not experimental results support

purpose/hypothesis.

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Explains why the results support or don’t support the origi-nal purpose/hypothesis• Compare the experimental results to the theoreti-

cal predictions.

• Explain why the results support or don’t support the purpose/hypothesis.

Addresses other issues pertinent to the lab and their effect on the results• Discuss at least three potential sources of error.

Potential sources of error are things that you know happened and things that could have happened. For each source of error, you should have three things:

1. Describe in detail the error that could have occurred.

2. Explain exactly how the error would have af-fected the results. Do not say “The results would be skewed.” Be specific and state if results would be lower or higher than expected.

3. Explain how the error could have been prevented.

• Example: Loss of sample on the filter paper would have resulted in a lower mass of product. This would have caused the mass percent of copper in the final formula to be lower than the theoretical value. This could have been prevented by transfer-ring the sample more carefully from the filter paper into the beaker.

• Addressing sources of error requires a critical review of each step of the experiment rather than saying “I messed up” or “we didn’t know what we were doing.”

ConclusionThe conclusion gives you the opportunity to discuss what you learned in this experiment. It can be written in first person (i.e., “I learned…”). This is also an op-portunity for the TA to evaluate your understanding of the experiment and related concepts through your work in the lab, how you worked with your lab partner, and through an evaluation of your lab notebook.

Convincingly describes what has been learned in the lab• State what you have learned and how it relates to

other topics or to real-life situations.

• Give any reasonable suggestions for improving the experiment.

• You should not describe your lab partner’s ability or inability to function in a lab setting.

Has successfully learned what the lab is designed to teach• The TA will evaluate your understanding of the

topic based on the overall quality of your report, your work in the lab, and the information entered into your lab notebook.

• Ask questions about concepts you don’t understand.

• Work with your lab partner to complete the experiment.

• Include all data and observations in your lab note-book and do so following the guidelines given at the beginning of this chapter.

PresentationWhenever you are submitting your work to someone else to read, you should pay attention to the general appearance and formatting. Remember that your TA will be reading your report on a computer screen so you want to make sure it is legible and easy to read.

When referencing other sources, including this lab manual, you should use the MLA style. Some simple examples are shown below, but if you have questions refer to a style guide. Additional help is available in the Writing Center (more information at http://www.uky.edu/AS/English/wc/).

Original Text from Advanced Inorganic Chemistry by F. Albert Cotton and Geoffrey WilkinsonCrystalline hydrates of metal ions and of organic sub-stances, especially those with N–H and O–H bonds, are numerous. For metal ions, the oxygen is always bound to the metal and the lone pairs on it can be directed toward the metal and involved in bonding but can, however, also form H bonds.

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Paraphrase and In-Text CitationMany metal ions can form crystalline hydrates (Cot-ton 96).

Quotation and In-Text CitationFor the crystalline hydrates of “metal ions, the oxygen is always bound to the metal” (Cotton 96).

or

Cotton states that for the crystalline hydrates of “metal ions, the oxygen is always bound to the metal” (96). Bibliography/Works CitedBook with one or more authorsAuthor(s). Title of Book. Place of Publication: Publisher, Year of Publication.

ExampleCotton, F. Albert & Geoffrey Wilkinson. Advanced Inor-ganic Chemistry. New York: John Wiley & Sons, 1988.

Web SiteBefore you use a Web site as a reference, make sure you evaluate the quality of the content. Just because it is posted on the internet doesn’t mean it is true.

Use of Wikipedia has its place, but is not appropriate for information that can be found in your textbook or this lab manual.

Author(s). Name of Page. Date of Posting/Revision. Name of institution/organization affiliated with the site. Date of access <electronic address>.

For additional information on the MLA style, check out the following resources:• http://owl.english.purdue.edu/owl/

resource/557/01/

• http://www.bedfordstmartins.com/online/cite5.html

Citations and References Are Formatted Correctly• In-text citations are included for any paraphrased

or quoted material. Remember that direct quota-tions must have quotation marks and a reference.

• In-text citations should include author’s name and page number.

• References should have all the necessary information.

• Include an alphabetized list of references at the end of your report.

• When referencing a Web site, follow the style above and include the month and year the page was accessed.

Formatting of Reports Is Correct• Use subscripts and superscripts in chemical and

mathematical formulas.

• Use the correct type of arrows in all reactions.

• Use Equation Editor when typing mathematical formulas.

• Follow any guidelines for margins, fonts, etc. as given by your TA (see page 23).

Report Is Written in Scientific Style• All statements and explanations are logical.

• Make sure that relationships between theoretical concepts are clear.

• Do not include unnecessary information (i.e., “This report isn’t very good because I was out of town this weekend” or “I couldn’t complete the calculations because I didn’t write down my data and my lab partner didn’t send it to me.”).

• Do not repeat information unless it adds some value or insight to the concepts discussed in the report.

• Use third person in the report (first person is ac-ceptable only in the conclusion).

• Proofread your report before submitting. It is usu-ally best to let it sit for a day (or at least a few hours) and then reread the report. You might catch errors in grammar or spelling or realize that you omitted some important information.

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Grammar and Spelling• Proofreading your report, perhaps out loud, will

help you detect grammatical errors.

• A list of common grammatical errors can be found at http://bcs.bedfordstmartins.com/everyday_writer3e/20errors/ or search on an internet search engine such as www.google.com for “common errors in grammar.”

• Since all reports are typed on a computer, use the spell-check feature in your word processor. For words not in the standard dictionary, such as chemical names, look them up in your lab manual, textbook, or use an internet search engine such as www.google.com to find the correct spelling.

• Make sure all sentences are complete sentences and have subject–verb agreement.

• If you need help with your writing skills, visit the Writing Center on the 5th floor of the W. T. Young library. More information about the Writing Cen-ter can be found at http://www.uky.edu/AS/English/wc/. You can go to the Writing Center for help or use some of their online resources (look under “Student Resources”).

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Semester and Year ________________________________________________________________________

Room Number CP-

Information About My TA Name (first and last) ________________________________________________________________________

Contact Information ________________________________________________________________________ (e-mail and/or phone)

Office Hours ________________________________________________________________________ All office hours are held in CP-25, the General Chemistry Learning Center.

Other Information ________________________________________________________________________

Formatting Preferences for Lab ReportsAsk your TA the following questions so that you know exactly what they want. Since they are the one grading your report, it is in your best interest to follow their formatting preferences. If they request something specific and you do not know how to do it, you can ask them or look in the help files of your word processing program.

1. Do you have a preference for single or double spacing?

2. Do you prefer a particular font? What about font size?

3. What size margins do you prefer?

4. Do you want a separate title page or can the title be at the top of the first page?

5. Should references be listed on a separate page or can they be placed at the end of the conclusion?

6. Do you have any preference for formatting tables, such as showing all gridlines?

7. Do you have any other preferences for the format of lab reports?

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Techniques for General Chemistry Lab

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One of the goals of this course is to teach students some basic laboratory techniques that they will use in this course as well as in future laboratory courses. Using correct techniques is important for several reasons. Proper technique:

1. reduces the error in experimental results.

2. prevents damage to equipment.

3. prevents contamination of reagents.

4. helps maintain a safe environment in the lab.

Dispensing SolidsReactions are performed using reagents in both the liquid and solid phase so it is im-portant to know how to dispense solids from the stock reagent bottle. The following steps should be performed when dispensing solids from a reagent bottle:

1. Obtain a small beaker, watch glass, or weigh boat to transfer the solid reagent.

2. Determine the approximate amount of the solid needed.

3. Locate the stock reagent bottle.

4. Remove the lid and lay it top-down or hold the lid. Never lay lids facedown as this can lead to contamination of the stock reagent.

5. Pour the approximate amount of solid needed into your container. Rotate the bottle slowly to help pour the sample slowly without getting too much.

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6. Replace the lid on the reagent bottle and take your sample to your bench or the balance area.

Some additional tips for dispensing solid reagents.• Whenever dispensing solids, you should be careful

not to create a “dust cloud” of the chemical to avoid inhalation and eye exposure.

• Always leave stock reagent bottles in their original location so that everyone has access to them. Never take reagent bottles to the balance area or to your bench.

• Never insert a spatula or any other object into the stock reagent bottle in order to prevent contamination.

Dispensing LiquidsLiquids tend to be easier than solids to obtain since they are easier to pour and it is easier to estimate the volume of a liquid than the mass of a solid. The follow-ing steps should be performed when dispensing liquid from a reagent bottle:

1. Obtain a small beaker or test tube to transfer the liquid reagent.

2. Determine the approximate amount of reagent needed.

3. Locate the stock reagent bottle.

4. Remove the lid and lay it top-down or hold the lid. Never lay lids facedown as this can lead to contamination of the stock reagent.

5. Pour the approximate amount needed into your container. Measure the exact volume needed when you return to your bench. If you take the time to measure exact volumes at the stock reagent area, you cause delays for other students.

6. Replace the lid on the reagent bottle and take your sample to your bench.

Some additional tips for dispensing liquid reagents.• Never return excess reagents to the stock bottle.

• Wipe up any spills to avoid any injuries when someone else comes to the stock reagent area.

• Never insert a dropper or any other object into the stock reagent bottles in order to prevent contamination.

• Always leave stock reagent bottles in their original location so that everyone has access to them.

• Concentrated acids and bases should be used in the hood. Do not remove the bottles from the hoods.

• The brown dropper bottles used for concentrated acids and bases should be tilted to dispense the reagent. Do not remove the lid.

Using an Analytical BalanceThe analytical balance is often used in many chemis-try laboratories. It allows us to determine the mass of a substance. Although the terms mass and weight are frequently used interchangeably, they are not the same thing. Mass is the amount of something while weight is a measure of the pull of gravity on the object. Mass is independent of location, while weight is not. The mass of an object on the moon will be identical to its mass on Earth. The weight of an object will change. For example, a 100-pound object on Earth will weigh 16.5 pounds on the moon and 234 pounds on Jupiter.

Most labs use electronic analytical balances but some still use what is known as a triple beam balance. The General Chemistry Labs use electronic analytical bal-ances which look similar to that shown in Figure C3.1. To increase the accuracy of your measurements, always use the same balance throughout an experiment.

1. Turn the balance on and check that all doors are closed or cover is on.

2. Press the “0/Tare” button to set the balance to zero.

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Balance pan

Figure C3.1. Electronic analytical balance.

Tare means to adjust the zero point on a balance.

3. Place the object on the balance pan and close the doors or replace the cover.

4. Allow the value to stabilize and record all digits on the display in your lab notebook.

5. Remove the sample from the balance.

6. Use the brush to remove any solids from the balance.

7. Close the doors or replace the cover and turn off the balance.

Some additional tips for using an electronic analytical balance:• Balances are fragile pieces of equipment. You should

not move a balance except when necessary. Always open and close cover gently.

• Never take reagent bottles to the balance area. Get the approximate amount needed in a beaker or other container and take that to the balance area.

• Never return excess reagent to the stock bottle. If you have excess reagent, offer it to someone else or dispose of it correctly. Do not leave it in the reagent area or near the balances.

• Use a weigh boat (see Figure C3.2) or a small beaker to hold the sample.

• Never pour reagents into a container in the balance. Always remove the container, add the reagent, and then place in the balance.

• Record all digits given on the display so that you can keep as many significant figures as possible after your calculations.

• Always clean the balance after each use.

©Hayden-McNeil, LLC

Figure C3.2. Weigh boat.

Using a Graduated CylinderOne piece of glassware commonly used in lab is a gradu-ated cylinder which is used to measure the volume of liquids needed. Graduated cylinders come in many sizes, from 10 mL (or smaller) to 4 L. The following steps should be used when measuring the volume of a liquid using a graduated cylinder:

1. Obtain a clean, dry graduated cylinder.

2. Pour the amount needed into the cylinder.

3. Record the exact volume used rather than trying to obtain the volume listed in the procedure.

a. Look for the bottom of the meniscus (see Figure C3.3). The meniscus will be much less promi-nent in plastic than in glass due to differences in the adhesive interactions between the liquid and the container.

b. Position yourself so that your eyes are level with the meniscus.

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c. Using the markings on the cylinder, determine the volume of the liquid in the cylinder.

d. Always estimate one additional decimal place beyond the markings of the cylinder when reading the volume to improve the accuracy of your value. It is assumed that the last digit has been estimated.

4. Add the liquid to the reaction as directed in the procedure.

5. Clean the cylinder to prevent contamination with its next use.

Some additional tips for using a graduated cylinder:• Always estimate one additional decimal point.

Looking at the example shown in Figure C3.3, we can see that the volume is between 88 and 89. By estimating the next digit between these two mark-ings, we increase the accuracy of our measurement. Since the last decimal place is assumed, someone seeing a volume of 88 mL would think it is between 80 and 90. If someone sees a volume of 88.6 mL, then this lets them know the volume is between 88 and 89 which is a far more accurate description of the volume of the liquid.

• Volumes given in the procedure are approximate. It is more important to record the actual volume used rather than spending time trying to get to the exact volume listed in the procedure.

• Use the smallest graduated cylinder that will contain your sample for increased accuracy. For example,

• Use a 10 mL cylinder to measure 3 mL of solution.

• Use a 50 mL cylinder to measure 18 mL of solution.

• Never return excess reagent to the stock bottle. If you have excess reagent, offer it to someone else or dispose of it correctly.

• Volumetric glassware usually has markings indicat-ing if they are “TD” or “TC,” which stand for “to deliver” and “to contain.” A temperature is also listed which indicates the temperature at which the cylinders are calibrated. If used at a different tem-perature, there can be some error in the measured volume.

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Meniscus

Eye level

Figure C3.3. Determining the volume in a graduated cylinder.

Using a BuretAnother piece of volumetric glassware is called a buret. A buret is often used when the amount of liquid to be added to the reaction is unknown. The liquid can be dispensed from the buret as needed and the volume is determined by recording the initial and final volume of the buret. To use a buret, do the following:

1. Obtain a clean, dry buret, a ring stand, and a buret clamp.

2. Set up the buret as shown in Figure C3.4.

3. Close the stopcock (handle should be perpendicular to the buret). Put a small beaker under the buret in case there are any leaks.

4. Use a funnel and fill the buret with the necessary solution.

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Buret clamp

Buret

Flask

Ring stand

5. Remove the funnel from the buret.

6. Open the stopcock (handle should be parallel to the buret) to allow 1–2 mL of liquid to drain from the buret. Repeat if there are still air bubbles present in the tip of the buret.

7. Record the initial volume (see Figure C3.5). The initial volume does not have to be at zero. It will save you time and effort if you just record the initial volume as it is instead of trying to get the initial volume to zero. Estimate one decimal place beyond the markings on the buret.

8. Dispense the amount of liquid needed. Be careful not to dispense past the bottom markings on the buret.

9. Record the final volume (see Figure C3.5), estimat-ing one decimal place beyond the markings on the buret. Subtract the initial volume to determine the volume dispensed.

Some tips on using a buret:• The volume markings go from top to bottom.

• Always estimate one additional decimal point. By estimating the next digit between these two markings, we increase the accuracy of our measurement.

• Remove the funnel and check for air bubbles before recording the volume.

• If you need more volume than the buret contains, record two pairs of initial and final volume data and combine the differences from the two pairs.

• If you have a broken buret, please take it to your TA. The tip and stopcock can be replaced and the barrel can be repaired, depending on the location of the break.

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Initial volume0.40 mL

Final volume23.80 mL

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Figure C3.4. Setting up a buret. Figure C3.5. Reading the initial and final volumes on a

buret.

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Gravity FiltrationSeparations play an important role in chemistry and range from separating a solid from a liquid to separating two isomers of a compound. Gravity filtration is one of the simplest forms of separation and is used to sepa-rate a liquid from a solid. Much like you drain cooked spaghetti in a colander, a solid can be separated from a liquid by pouring the sample through a piece of filter paper in a funnel. Think of the filter paper as a colander with really, really small holes in it. To perform a gravity filtration do the following:

1. Obtain a funnel, filter paper, and flask. If you want to filter the liquid into a beaker, you would also need a ring stand and an iron ring.

2. Initial the filter paper with a pencil and find its mass.

3. Fold the filter paper in quarters and then open into a cone (see Figure C3.6a). Place the cone into the funnel which can be inserted into the neck of the flask or placed in a ring over a beaker (see Figure C3.6b).

4. Wet the filter paper with the solvent of the solution being filtered (commonly distilled water).

5. Using a stirring rod to help, pour the liquid into the funnel. Then use a wash bottle to wash the remain-ing sample out of the beaker (see Figure C3.7).

6. Rinse the solid a few times with an appropriate solvent.

7. Allow the filtration to continue for several minutes after it appears complete. This allows any additional solution to filter through which will require less time for the solid to dry, if applicable.

8. Remove the filter paper from the funnel, place on a pre-massed watch glass, and place in an oven to dry.

Some tips for doing a gravity filtration:• If the solvent used is flammable, use caution when

heating a sample to dry. Liquids such as ethanol and acetone have low flash points which are the lowest

temperatures at which the vapors of the liquid can ignite in air. Use caution when placing samples rinsed with flammable solvents in the oven.

• Do not overfill the funnel when adding the sample to the funnel. Make sure the liquid does not go above the top edge of the filter paper.

Vacuum FiltrationWhile gravity filtration is effective, it can be slow and vacuum filtrations are usually much more efficient than gravity filtrations. A Büchner funnel is one type of fun-nel that can be used for a vacuum filtration. It is shaped differently from a regular funnel and has many small holes instead of one large hole. Rather than waiting for the liquid to go through the filter paper on its own, a vacuum filtration pulls the liquid through. A vacuum can be created in a filtration flask when the filter flask is connected to a water aspirator. As water flows down through the faucet, air is pulled in through the side arm and out of the connected flask. This creates a vacuum in the flask which then pulls the liquid through the Büchner funnel and filter paper.

1. Obtain a Büchner funnel, filter flask, vacuum tubing, filter paper, ring stand, clamp, and clamp holder.

2. Initial the filter paper with a pencil and find its mass.

3. Set up the funnel as shown in Figure C3.9 and place the piece of filter paper in the funnel. The filter paper should lay flat in the funnel.

4. Connect the vacuum tubing to the side arm of the aspirator on the faucet (see Figure C3.8).

5. Turn the water on.

6. Use a small amount of the solvent to wet the filter paper.

7. Using a stirring rod to guide the solution, pour the sample to be filtered onto the filter paper. Pour small portions to avoid getting solid underneath the filter paper.

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Fold inquarters

Open outinto cone

Fold inhalf

Crease paperslightly


©

Hay

den-

McN

eil,

LL

C

Figure C3.6a. Folding filter paper for gravity filtration. Figure C3.6b. Setting up for gravity filtration.

Tip of funneltouches thebeaker wall


Figure C3.7. Performing a gravity filtration.

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8. Allow the filtration to continue for several minutes after it appears complete. This allows any additional solution to filter through which will require less time for the solid to dry, if applicable.

9. Disconnect the tubing to break the vacuum before turning off the water.

10. Use a spatula to help remove the filter paper from the funnel. Place the filter paper on a pre-massed watch glass and place in oven to dry.

11. Check the procedure for the experiment to deter-mine whether the filtrate (liquid) should be pre-served for additional experiments or disposed of.

©H

ayden-McN

eil, LL

C

Figure C3.8. Aspirator connection.

Some tips when doing a vacuum filtration:• If you notice a leak under the sink, disconnect the

vacuum first and then turn off the water. Notify your TA.

• If the solvent used is flammable, use caution when heating a sample to dry. Liquids such as ethanol and acetone have low flash points which are the lowest temperatures at which the vapors of the liquid can ignite in air. Use caution when placing samples rinsed with flammable solvents in the oven.

©H

ayden-McN

eil, LL

C

Filter paper

Büchner funnel

Stirring rod

To aspirator on water faucet

Filtration flask

Filtrate

Figure C3.9. Vacuum filtration setup.

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Using MeasureNet and Probes

C h a p t e r 4

Students will collect data in the lab using the MeasureNet workstation and a variety of probes. The workstation is the user interface which allows students to set up experiments, and then collect data which is then uploaded to the Chem21 server where it can later be retrieved to complete the data analysis for the experiment. The data is displayed on the workstation display as it is collected. The probes connect to the workstation via the ports on the bottom of the workstation. Figures C4.1 and C4.2 show a picture of a student workstation with the buttons divided into groups based on their function as well as the bottom of the workstation where the probes are connected.

Please be aware that components of electronic data collection systems are expensive and must be handled with care. Follow the directions carefully to both collect good data and to protect the equipment.

The TA in the lab will log students into the workstation and can monitor their data col-lection throughout the lab session. Once logged in, students can begin to collect data. Do not begin work until your TA has confirmed that you are logged in to the correct workstation. The instructions on the following pages provide a general outline for use of the MeasureNet workstation and probes. However, students are expected to adapt these instructions for the specific experimental needs as they write their procedures. Carefully read the information on the display as there is sufficient information there to help guide you to the next step.

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C h a p t e r 4 • Using MeasureNet and Probes

Chapter

4Figure C4.1. Front view of MeasureNet workstation.

Figure C4.2. Bottom view of MeasureNet workstation.

Operation of the MeasureNet Workstation1. Connect the appropriate probe to the workstation.

2. Press the power button on the workstation and see that the status is “online.”

3. Press “MAIN MENU” to see a list of probes.

4. Use the function keys (F1, F2, etc.) to select the correct probe.

5. Use the function keys again to select the appropri-ate type of experiment (e.g., temperature vs. time, pressure and temperature, etc.).

6. When indicated in the probe instructions, select “CALIBRATE” and follow the directions on the display.

7. Choose “SETUP” to specify limits of the axis (i.e., the probable range of your data) for display purpos-es. Values outside these limits will still be collected but will not appear on the workstation display.

a. After data collection is complete, you can change the limits to replot the current data set.

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8. Use the arrows to highlight (look for asterisks on either side) the value that needs to be changed, type in the correct value, and press “ENTER.”

9. Select “DISPLAY” to accept all values.

10. Press “START/STOP” to start data collection. Data will continue until the x max value or until you press “START/STOP” again.

pH Electrode and CalibrationFor this titration experiment, we will use a pH electrode to measure the change in pH as we add the standard solution to our analyte solution. In order to obtain ac-curate data, the pH electrode must be calibrated against solutions of known pH. Because we will be measuring pH values over a wide range, we will calibrate the elec-trode against two solutions with pH values of 4.00 and 10.00. It is only necessary to calibrate before the first titration that you perform in lab that day. Changes in signal from the electrode do change over time but the change during one lab period is not significant.

The pH electrode is a delicate and expensive piece of equipment. Use caution to avoid breaking the tip and do not use it to stir a solution. The only moveable/removeable part on the electrode is the storage bottle.

Drop CounterWhen using the pH electrode, we will also be using a device known as a drop counter. As each drop of liquid passes through the “counting slot” with its infrared beam, it is counted. By entering both the initial and final volumes on the buret, the average drop size can be de-termined, which, along with the number of drops, will allow us to graph a pH vs. volume curve. This titration curve can then be used to determine the equivalence point which is then used to determine the concentra-tion of the analyte (unknown) solution.

When using a drop counter, it is imperative that you set the equipment up correctly and that the solution dispensed from the buret is done so in drops. If the buret is opened to allow a constant flow of liquid, the data will be unusable.

Figure C4.3. Drop counter.

Calibration1. Obtain a pH sensor, ring stand, drop counter, and

any needed clamps. Complete the setup of the drop counter and pH electrode as shown in Figures C4.3 and C4.4.

2. Obtain approximately 20–25 mL of each of the buffers (pH 4.00 and pH 10.00) in separate plastic 50 mL beakers. These will be used to calibrate the pH probe and should not be used for any other purpose.

3. Remove the storage bottle from the pH electrode, connect it to the workstation, and insert it into the opening on the drop counter so that the cap rests in the recess.

4. Rinse the pH electrode with distilled water and collect the waste into a 250 mL beaker. This will be used as your waste beaker throughout the experiment.

5. Use a thermometer to measure the temperature of the pH 4.00 buffer solution and record the value.

6. Place the pH 4.00 buffer solution underneath the pH electrode and lower the electrode into the solution.

7. Press “MAIN MENU” on the workstation and select “pH/mV” from the menu and then select “pH v Volume.”

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8. Select “CALIBRATE” and the workstation will prompt you to enter the temperature and the cor-rect pH of the solution (e.g., 4.00).

9. Once the pH reading on the screen stabilizes, press “ENTER.” The value on the screen may not read 4.00; you are just waiting for the value to stop changing.

10. When prompted, enter the pH of the second buffer solution (e.g., 10.00). Remove the electrode from the first buffer solution and rinse well with distilled water into your waste beaker.

11. Place the beaker with the pH 10.00 buffer below the electrode and lower it into the solution.

12. Once the pH reading on the screen stabilizes, press “ENTER.” The value on the screen may not read 10.00; you are just waiting for the value to stop changing.

13. Press “DISPLAY” on the workstation. The pH value should be within 0.05 of the actual pH of the second buffer solution. If not, you need to redo the calibration.

14. Raise the pH electrode and remove the buffer solu-tion. Rinse the electrode well with distilled water.

Titration1. Obtain approximately 40–50 mL of your titrant

(usually your solution of known concentration) in a 100 mL beaker.

2. Rinse the buret with 3–5 mL of the titrant by pour-ing it in the buret so that it covers all sides and then draining it into your waste beaker. Do three rinses.

3. Attach a buret clamp to the ring stand and insert the buret so that the tip of the buret is directly over the “counting slot” on the drop counter. The solution from the buret must drop through the counting slot to collect data.

4. Place the waste beaker underneath the buret and close the stopcock.

5. With a funnel, fill the buret with the titrant solu-tion. Remove the funnel.

Figure C4.4. Titration setup.

6. Open the stopcock to drain enough titrant to fill the tip (~1–2 mL). At this time, you also need to determine how far to open the buret so that the solution drips from the buret. The solution must drip in order to collect data.

7. Once you have found where to turn the stopcock so that the solution will dispense dropwise, close the stopcock and remove the waste beaker.

8. Obtain a sample of the analyte (usually the un-known solution). Remember that the larger volume used, the longer it will take to titrate (<25 mL is usually a safe place to start). Using a graduated cylinder, determine the exact volume. Don’t forget to estimate one decimal place beyond the markings on the glassware!

9. If needed, add distilled water to the beaker so the total volume (distilled water plus analyte) will be ~40–50 mL of solution in the 150 mL beaker and then add the known volume of the analyte solution.

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10. Place the 150 mL beaker underneath the drop counter and lower the pH electrode into the solu-tion. The pH electrode should be just above the bottom of the beaker so that you can gently swirl the solution.

11. Check that the buret tip is directly over the “count-ing slot” so the drops will go through the opening and into the beaker. Do not open the stopcock yet.

12. Begin the titration by pressing “START/STOP.” The workstation will prompt you to enter the initial volume. Enter the actual volume reading from the buret. Remember to record the volume to the sec-ond decimal place when you estimate one decimal place beyond the markings on the buret. The buret does not have to start at zero.

13. Carefully, turn the stopcock on the buret so that the titrant drips into the analyte solution. You may need to make small adjustments to the stopcock so that the solution continues to drip at approximately 1 drop per second. The red LED light will flash each time it detects a drop.

14. Gently swirl the beaker while the titrant is being added, being careful to keep the beaker under the buret at all times.

Figure C4.5. Typical titration curve.

15. Allow the titrant solution to drip into the analyte solution until the titration is complete. When complete the pH value will plateau (~10–12 for a basic titrant and ~1–4 for an acidic titrant).

16. When complete, simultaneously press “START/STOP” on the workstation and close the stopcock on the buret.

17. Record the final volume reading in your lab note-book and enter it into the workstation.

18. Continue by saving the data (see directions on page 41).

19. Refill buret as needed and repeat until experiment is complete. At least three good titrations should be collected for each set of needed titrations. This may mean that you need to collect at least four titrations so that the outlier can be excluded.

20. Dispose of waste in the appropriate location and clean all equipment and glassware before returning it to the correct location.

21. Rinse the pH electrode with distilled water, remove it from the drop counter, and replace the storage bottle. The electrode needs to be stored wet in the storage solution, not in distilled water and never stored dry. See your TA if you need additional stor-age solution.

22. Carefully, wipe any liquid from the surfaces of the drop counter.

Reminders for Use• Always rinse the probe with distilled water after

each use.

• Store only in the pH storage solution. Never store dry or in water.

• Calibrate at the start of the lab session.

• Solutions must drop through the drop counter. A flow of solution will cause errors in your data.

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Pressure ProbeThe pressure probe can be used to measure the pressure of the contents in a container. It measures “gauge pres-sure,” which is the difference in pressure between the atmospheric pressure and the pressure of whatever is connected to the probe. Like an open-ended manom-eter, you need to add the reading from the gauge and the atmospheric pressure to get the actual pressure. The atmospheric pressure can be found on the barometer located in the lab.

Figure C4.6. Pressure probe.

Calibration1. Connect the pressure sensor to the workstation

without anything attached to the sensor.

2. Press “MAIN MENU” on the workstation. Press the appropriate function key to select “PRESSURE.”

3. Use the function keys to select “PRESSURE & TIME.”

4. Press “CALIBRATE” and follow the instructions on the screen.

5. Press “DISPLAY.”

Measuring Pressure vs. Time1. Attach the tubing to the connector in the stopper.

2. Prepare, but do not mix, any solutions needed.

3. Mix the solutions and quickly insert the stopper into the container.

4. Allow data to collect until experiment is complete.

5. If you do not see an increase in pressure, repeat the trial and check your system carefully for leaks.


7. Repeat as needed for additional trials. Reminders for Use• Do not over-tighten the fittings. Stop when you

feel resistance.

• Do not attempt to remove tubing from sensor.

• Hot plates are hot; plastic melts. Use caution when using probes and hot plates at the same time.

Temperature ProbeThe temperature probe can be used in the range of –50°C to 125°C and can be used in a variety of sub-stances. While calibration is necessary to determine an accurate temperature relative to an external accepted value, many experiments are more focused on the

Figure C4.7. Pressure probe connections. A. Direct connection of the syringe; B. Four-way stopcock connection;

C. Luer-to-hose barb fitting.

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change in temperature. In these cases, the absolute tem-perature is not important as long as the probe behaves uniformly (i.e., offset by 1°C throughout the range of measurements).

Figure C4.8. Temperature probe.

Measuring Temperature1. Connect the clamp to the ring stand to hold the

temperature probe.

2. Connect the temperature probe to the MeasureNet workstation.

3. After verifying that your TA has logged you in to the workstation, press “MAIN MENU” on the workstation.

4. Select “TEMPERATURE.”

5. Select “TEMP v TIME.”

6. Select “SETUP” to check limits which are deter-mined by the range of experimental values you expect. Data outside this range will still be collected but will not appear on the display. If necessary, press the arrow keys to select which variable to edit (marked by asterisks on either side of value), key in the new value and press “ENTER.”

7. Once the experimental setup is complete, press “START/STOP” on the workstation to begin collect-ing data.

8. Once data collection is complete, press “START/STOP.”

9. Rinse the temperature probe with distilled water and dry. Return to the correct storage location.


Reminders for Use• Hot plates are hot; plastic melts. Use caution when

using probes and hot plates at the same time.

ColorimeterA colorimeter can be used to measure the amount of light of a particular wavelength. Unlike scanning instru-ments which scan a range of the electromagnetic spec-trum (e.g., infrared, visible, X-ray, etc.), a colorimeter monitors a single wavelength. Light of the appropriate wavelength is absorbed by the solution. As the concen-tration of the absorbing species increases, the amount of light absorbed will increase. Sometimes the value is reported as the percent transmittance which is inversely proportional to the absorbance.

Figure C4.9. Colorimeter.

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The colorimeters used in the lab are known as dual-beam colorimeters because there are two beams of light that will go through two paths inside the colorimeter. One of the beams will go through a cuvette containing the solvent or other appropriate solution (cell holder “R”) to account for any light absorbance by the cuvette and/or the solution/solvent. This will be known as the blank or reference solution. The other beam will go through the sample (cell holder “S”) being studied so the reported value will actually be a reporting of the difference in the amount absorbed between the two samples, which gives us a direct relationship between the concentra-tion of the light-absorbing species and the amount of light absorbed. The use of a dual beam also eliminates variations in the signal due to changes in the intensity of the light.

lightsource

beamsplitter

R

ratio display

S

detector

detector

Figure C4.10. Dual-beam schematic.

The color of a substance is determined by its interaction with light. We can see blue because a sample absorbs all colors of light except blue, which is reflected. Alter-natively, we can see blue because its complementary color (the color across from it on the color wheel) is absent from the light.

Measuring Absorbance1. Connect the colorimeter to the workstation.

Make sure no other probes are connected to the workstation.

2. After verifying that your TA has logged you in to the workstation, press “MAIN MENU” on the workstation.

3. Select “COLORIMETRY/FLUOR/TURB” and then select “COLORIMETRY.”

4. Use the function key to select the appropriate wavelength.

5. Select “KINETICS” on the workstation.

6. Obtain the necessary reagents.

7. Prepare your blank or reference solution which should contain everything except the light absorb-ing species.

a. Always record the exact volumes used since it is unlikely that you will get the exact amounts. For example, instead of 1.00 mL, you might have 1.08 mL. It is very important that you record the exact volume so that your concen-trations will be correct in the graph which will be used to determine the concentration of the unknown.

8. Prepare solutions as needed for the experiment.

9. Rinse both of the cuvettes twice with the blank solution. Rinsing involves pouring a small amount of a solution in a cuvette and pouring it out. This removes any residual liquids from the cuvette to make sure the concentration of the solution is not affected by those residual liquids. Dispose of the rinsings in the appropriate manner.

10. Fill the cuvettes with the blank solution and cap the cuvette. Use a lint-free tissue to wipe the sides of the cuvette being careful to hold the cuvette by the top to avoid fingerprints on the sides.

11. Place one of the cuvettes with the blank solution in the cell holder marked “R.” Use care when inserting the cell in the holder as it is designed to hold the cuvette by the corners only (see Figure C4.11).

Cuvette position


Cuvette holder

Figure C4.11. Cuvette holder in colorimeter.

12. Place the second cuvette with the blank solution in the cell holder marked “S.”

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13. Slide the colorimeter lid closed and press “ENTER.” The minimum and maximum percent transmit-tance will be adjusted at this time and will take approximately 10 seconds to complete.

14. After this is complete, select “DISPLAY.”

15. Leave the blank solution in the cell holder marked “R” and remove the blank solution from the cell holder marked “S.”

16. Rinse the second cuvette with your first solution.

17. Fill the cuvette with your first solution and cap the cuvette. Use a lint-free tissue to wipe the sides of the cuvette being careful to hold the cuvette by the top to avoid fingerprints on the sides.

18. Place the sample cuvette into the cell holder marked “S.” Use care when inserting the cell in the holder.

19. Wait until the value has stabilized and then, in your lab notebook, record the absorbance for the solution.

20. Pour the solution into a waste beaker.

21. Repeat steps with sample solutions until the absor-bance for all have been measured. Leave the refer-ence cuvette in the colorimeter for the duration of the experiment.

22. Pour the solutions from both cuvettes into a waste beaker.

Check with your TA to see if you will enter data now or on Chem21.

23. Push the “MAIN MENU” key and then select “OTHER.”

24. Select “MANUAL ENTRY.”

25. Key in the value of the exact concentration for your first solution and press “ENTER.” You will need to calculate this before entering your values.

26. Key in the value of the absorbance for your first solution and press “ENTER.”

27. Repeat for each of the solutions. Double-check all values before saving data. If you need to change the data, use the arrow keys to select a data point and then key in the new value and press “ENTER.”

28. Continue by saving the data (see directions below).

Reminders for Use• Use care when placing cuvettes into the colorimeter

to avoid scratching the cuvette and to avoid spilling solution into the colorimeter. While colorimeters are built to be durable, spilled liquids inside any electronic equipment can destroy it.

• Record exact volumes used.

• Always clean cuvettes with a lint-free tissue and handle carefully. Natural oils on your skin which are transferred to the cuvette will interfere with your results.

Saving Data1. After data collection is complete, press “FILE OP-

TIONS” and choose “SAVE.”

2. Enter the appropriate three digit code (see experi-ment information for details about what code to use). The code is important as it allows the data to be correctly imported into Chem21.

3. Press “ENTER.”

4. Check with your TA to make sure the file was saved and uploaded correctly.

5. Press “MAIN MENU” to start another trial, if needed.

Reminders• Data is saved automatically to Chem21.

• When you log in to Chem21, your MeasureNet data will be available. Other data (e.g., mass of substance) will be entered manually into Chem21.

• Data can also be downloaded from Chem21 for viewing and processing in an external program.

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CHEMISTRY - Chem21Labs · Experiment 7 Acid–Base Titration ... Experiment 9 Using Redox Chemistry...

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