Part-I Chem 105 Lab Manual PDF

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Summary

Lab Manual and procedure...

Description

Reports, Equipment, Data, and Techniques

UWM Department of Chemistry and Biochemistry September 7, 2017

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Contents I

Reports, Equipment, Data, and Techniques

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1 Laboratory 1.1 Preparing for Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Laboratory Notebook and Roports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Laboratory Grading Rubric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2 The Balance and Glassware 2.1 The Laboratory balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 Balance Cleaning Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Glassware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Measurements and Data 15 3.1 Precision and Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2 Percent Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3 Significant Figures and Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.4 Errors and Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4 Procedures and Techniques 4.1 Acid-Base Titrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Beer’s Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CONTENTS

Part I

Reports, Equipment, Data, and Techniques

Chapter 1

Laboratory To reduce the possibility of accidents, make sure to always follow the established safety procedures (these procedures will covered during your first laboratory). Students who repeatedly violate safety rules will not be allowed in lab.

1.1

Preparing for Laboratory

You will need to prepare before your scheduled meeting time for each laboratory experiment. To get the most out of performing experiments: • Read the experiment and make sure you know its general purpose. You will probably need to consult other sources such as your textbook and lecture notes. • Assemble everything you will need to carry out the experiment and calculate your results. For example, if the experiment requires accurate densities of water as a function of temperature you will need to locate the required values from your textbook, from sources in the library, or perhaps from the world wide web. • Follow directions carefully, and be sure you understand the purpose of each step. You will get very little out of the experiment if you do it without thinking. • Prepare your laboratory notebook (see Section 1.2) well before class. • Record everything in your laboratory notebook in ink (use a black ballpoint pen). If you make an error, put a single line through the text and continue right below. • Include proper references for all material consulted. These may be included as footnotes or collected into a separate section at the end of the report. • Follow all safety procedures and know the location of safety equipment such as the eye wash station, safety shower, fire extinguishers, and emergency exits. • Make sure to bring your safety goggles as they must be worn at all times when you are in lavatory.

1.2

Laboratory Notebook and Roports

If you go on to perform research or work as a chemist, you will be required to keep a proper laboratory notebook. In this course a more flexible style has been adopted. Your notebook should contain all the information needed to perform the experiment and your data, observations, and results. All entries must be done in ink (use a black ballpoint pen). The goal is to effectively and efficiently communicate what was done during laboratory. Expect that your instructor will check your notebook for completeness before you are allowed to start the experiment. For each experiment include:

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CHAPTER 1. LABORATORY 1. Print your name, laboratory section number, and the date on the top of each page of your notebook. Carbon-less copies are best as you must retain a copy of all work you submit for grading. Record everything in ink (use a black ballpoint pen). Page numbers must be sequential and your writing legible or the report will be graded as a zero (0). 2. Title of the experiment (as given in the manual). 3. Answers to all pre-laboratory questions (you can omit all but the ‘practical application’ question IF there was a quiz on D2L). 4. A brief statement of the objectives of the experiment. 5. The experimental procedure in outline form. Essentially, this will be the procedure given in the manual with any additional information you need to complete the experiment. 6. Data and observations. Data is best recorded in tables. Think about the best way to construct these as you prepare for the experiment. As a general rule, you should expect to perform triplicate analysis. Record observations such as color changes, the formation of a precipitate, or a change in the temperature of the reaction vessel as you preform the experiment. 7. Calculations and results. Make sure to include all equations. If the same calculation must be performed a number of times, only one of them should be recorded in detail. Use a spreadsheet program such as OpenOffice calc for plotting and repeated calculations. 8. Conclusions and final results. 9. References (if not included as footnotes).

1.3

Laboratory Grading Rubric

1. (2 points) Name, laboratory section number, and date on each page. 2. (2 points) Title (from the manual). 3. (20 points) Pre-Lab questions. A good answer for the ‘practical application’ question could result in the addition of up to five points (making the lab worth up to 105 points). The remaining questions are worth fifteen points, if there was a pre-lab quiz on D2L the points are assigned here and removed based on the score on D2L: 25 points Outstanding ‘practical application’ answer (see below). 20 points ‘Practical application’ question answered. 15 points ‘Practical application’ question not answered. If there was not a pre-lab quiz on D2L: 20 - 25 points All questions answered correctly and the ‘practical application’ question was answered to an additional depth (including detail beyond one or two sentences and possibly including secondary information). 15 - 20 points All questions answered correctly. 10 - 15 points All questions answered correctly with 1 or 2 incorrect answers, depending on the number of pre-lab questions (i.e. for pre-labs with 3 or 4 questions one incorrect answer constitutes 15 points; for pre-labs with five or more questions, two incorrect answers constitutes 15 points). 5 - 10 points All questions answered, but there were multiple incorrect answers. 0 - 5 points Most questions answered incorrectly or not attempted. 0 points All questions answered incorrectly or not attempted. 4. (3 points) Objective. 5. (7 points) Procedure. The procedure is outlined in individual steps that identifies:

1.3. LABORATORY GRADING RUBRIC

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• what the student is to do • when to record data

• safety issues or disposal directions • time(s) involved

7 points Procedure is complete and not missing individual steps or components listed above. 4 – 7 points Procedure is missing individual steps or one component listed above. 2 – 4 points Procedure is missing individual steps and/or one or two components listed above. 0 – 2 points Procedure is missing individual steps and/or two or three components listed above. 0 points Procedure is missing or inaccurate. 6. (20 points) Data and Observations. These must be recorded in real time, not added later. Sometimes observations are contrary to predictions, it is critical that they be recorded anyway. 10 – 20 points Includes actual amounts of materials used and complete observations detailing any color change, gas evolution, temperature change, etc. To receive maximum points these must be written in such a way that another chemist could use them as a reference. 5 – 10 points A complete report, but not terribly detailed would earn 20 points. This grade indicates that an important observation or a very small amount of data was missing. 0 – 5 points A report with very little detail. Missing data and observations. 0 points The section is missing or shows a gross lack of effort by the student. 7. (2 point) Names and signatures of all members of the assigned group (if applicable, otherwise added to the base). 8. (2 point) Serial numbers of equipment used (if applicable, otherwise added to the base). 9. (20 point) Calculations and Results. 20 points Calculations are correct and all results are presented with proper units. 10 – 20 points One of the follow possibilities occurs: – Calculations are correct and all results are presented but missing units (1 point per missing unit). – Calculations are incorrect with only one mistake in the process (even if it effects more than one calculation) but all results are presented. – All results are not presented, but calculations are correct for those presented. 5 – 10 points Two of the above occur. 0 – 5 points Calculations are incorrect, all results are not presented, units are missing or incorrect, or calculations are missing. 0 points Section is missing or all calculations are incorrect and all units are missing or incorrect. 10. (20 points) Conclusions. 15 – 20 points The conclusion: is related to the original problem, is supported by the data, and the implications are completely discussed with little or no error. 10 – 15 points The conclusion: is related to the original problem, is supported by the data, and the implications are partially discussed with some errors and omissions. 5 – 10 points The conclusion: draws upon the language of the experiment and presents scientific terms, but does not define or discuss the relevance to the original problem; is in conflict with the experimental results; is related to the problem but is supported by the data to a limited extent. 0 – 5 points The conclusion: is missing, illustrates inaccurate understanding of the scientific concepts underlying the experiment, is not related to the stated problem, or most implications are missing. 0 points The conclusion: is missing or the the conclusion is unrelated to the experiment and not supported by the results.

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CHAPTER 1. LABORATORY

11. (2 point) References (if applicable, otherwise this is added to the base). A few things take points right off the top. Write the penalty and reason right on their lab. -10 points If the lab was not legibly written in ink, double the points off if it happens a second time, and grade as zero (0) if it happens more than twice. -10 points The first time they miss any portion of the pre-lab talk or come in late, double it if it happens a second time, and record their grade as zero (0) if it happens more than twice. -10 points Each time you catch them without safety goggles write ‘-10 goggles’ on their lab. If it happens in a second lab, double the points off and they must see the instructor in charge of the course before they are allowed back in lab. Record all labs as zero (0) until you get a written note stating they are allowed back in lab. -10 points If they fail to clean up or put equipment away. -100 points Late labs are graded as zero (0). Put ‘Late ’ on the first page where is the date you received the report. Completed labs are due by the start of the next scheduled lab period.

Chapter 2

The Balance and Glassware The following are some general comments about measurements, the electronic balance, and some common glassware.

2.1

The Laboratory balance

You will use electronic balances to obtain the mass of objects. These measure the mass to within 0.001 g. To help ensure that you obtain the best results for your experiment: • The balance should be left on at all times. • Always use the same balance when making repetitive measurements. • Weigh materials at room temperature. • Never weigh objects directly on the balance pan. Always use some sort of a container. • Wait for the balance to stabilize before recording the mass. Record all digits shown on the display (estimate the last digit by averaging, if necessary). • When finished, remove your container and clean up any spills. • You may need to tare your container. Place the container on the balance and press the tare button. Once the reading stabilizes to zero the balance will record only the mass of the added sample, and will not include the mass of the container. The total mass (the mass of the container plus the mass of the sample) must not exceed the capacity of the balance.

2.1.1

Balance Cleaning Procedure

Balances must remain clean to function properly. Liquids spilled inside a balance require immediate attention. Notify your instructor and the laboratory technician immediately if you spill a liquid on a balance. To clean up a spilled solid: 1. Take care not to unplug the balance. They require re-calibration if the power is cut off. 2. Remove the weighing pan and brush any chemicals onto the table. Take care not to brush chemicals into the lower housing. 3. Remove the guard ring and brush any chemicals onto the table. The ring must be tilted slightly to get it out of the draft shield. 4. Brush out the base of the draft shield. Take care not to brush chemicals into the lower housing. 5. Replace the ring and weighing pan. 6. Use a damp sponge to clean the bench top between the balances.

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CHAPTER 2. THE BALANCE AND GLASSWARE

Figure 2.1: Beakers (left three) and Erlenmeyer flasks (right three) are designed for mixing and holding. The volumes, if any, stamped on the sides have considerable error. 7. Gently slide (do not pick up!) the balance to the just cleaned area and clean the rest of the balance area. 8. Slide the balance back into place. It should be approximately centered over the holes in the bench top with the sides parallel to the end of the bench. 9. Notify your instructor and the laboratory technician that the balance was moved for cleaning.

2.2

Glassware

You will use glassware in almost every experiment you preform. The type of glassware you choose depends on the nature of the task you need to complete. 1. Beakers and flasks (see Figure 2.1) are designed for mixing and holding. The volumes (if any) stamped on the sides have considerable error. 2. Graduated cylinders are used to deliver (TD) approximate volumes of solution. TD glassware has been calibrated to dispense a quantity of liquid knowing that some of the liquid will be left behind. 3. Burets are TD glassware (see Figure 2.2), but are designed to deliver variable volumes of solutions. The volume of a typical buret can be read to two decimal places. A bit of preparation is usually required before a buret can be used. • Rinse the buret with distilled water.

• If the water does not flow freely or drops adhere to the sides of the buret, the buret is not clean. Wash the buret with very dilute soapy water using a buret brush. Rinse thoroughly with plain water. Then rinse with two or three small portions of distilled water. • Rinse the clean buret with two 5-mL portions of the designated solution (the solution to be dispensed by the buret). • Half-fill the buret with the designated solution and discharge a small volume to ensure there are no air bubbles in the tip. • Fill the buret as required by the procedure.

• When reading a buret, read the bottom of the meniscus at eye level.

• To remove the last drop of solution, touch the tip of the buret to the inside of the receiving flask (the flask that receives the solution dispensed by the buret).

• The volume of solution delivered is the difference between the final and initial volumes. 4. Volumetric pipets are also TD glassware, but are designed to accurately deliver a specific volume of liquid. The pipet has one of the smallest margins of error for all dispensing glassware. For example, when properly used, a 5-mL pipet has been calibrated to deliver only ± 0.01 mL from the target volume. To ensure this level of accuracy, it must be properly used and cared for:

2.2. GLASSWARE

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Figure 2.2: Volumetric flasks (left and right) and a buret (center). Volumetric flasks are designed to contain (TC) the specified volume, while the buret is designed to deliver (TD) a specific volume knowing some liquid will remain.

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CHAPTER 2. THE BALANCE AND GLASSWARE • Clean a dirty pipet with very dilute soapy water. Rinse with distilled water.

• Transfer stock solution (the solution that will be used to fill the pipet) to a beaker. Never put a pipet directly into a stock solution. • Using a pipet bulb, carefully fill the pipet with a small amount of the solution. Rotate the pipet to wet the inside walls. Discard the solution into the proper waste container. • Fill the pipet with solution to a point above the calibration mark. Do not suck the solution into the bulb, remove the bulb and quickly cover the opening the pipet with your index finger. • Allow the solution to drain to the calibration mark. Make sure that there are no air bubbles in the pipet and that you read the the meniscus at eye level. Touch the tip of the pipet to the edge of the flask to remove the last drop of solution. • Touch the tip of the filled pipet to the lower inside wall of the receiving flask and allow the pipet to drain. As with all TD glassware, do not blow out the liquid remaining at the tip of the pipet.

5. Volumetric flasks are used to accurately prepare a solution of known concentration (see Figure 2.2). The volumetric flask is calibrated to contain (TC) a stated volume of liquid to four significant figures. To prepare a solution using a volumetric flask: • Clean and thoroughly rinse the flask. The last rinse is always done with the solvent so the inside of the flask can remain wet. • Unless specifically instructed differently, always prepare solutions at room temperature.

• To dilute a liquid: deliver a volume of concentrated liquid into the flask. Carefully add water (solvent) using a water bottle and disposable pipet to the calibration mark. Thoroughly mix by capping and then inverting. • To prepare a solution from solids: carefully place the correct amount of solid in the volumetric flask. Completely dissolve the solid in a minimum amount of solvent. Carefully add solvent (usually water) using a water bottle and disposable pipet to the calibration mark. Thoroughly mix by capping and then inverting.

Chapter 3

Measurements and Data The experiments in this manual require that you properly report your results from an experiment that demonstrates a (possibly) new technique. The following are some general comments about measurements and the treatment of data.

3.1

Precision and Accuracy

Making quantitative measurements is central to chemistry. The accuracy and precision of a measurement must always be considered. Accuracy is a measure of how close a measurement is to the actual or theoretical value. Precision describes how close a series of measurements are to each other. For a well designed experiment, it is usually the case that a precise series of measurements are also accurate.

3.2

Percent Error

The accuracy of a measurement can be evaluated by comparing the experimental result with the theoretical result. As a general rule, you should report the percent error as part of your results. Error %Error

=

(Experimental value) − (T heoretical value) | Error | × 100% = T heoretical calue
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