laboratory assignment laboratory techniques answers

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• Dr. John J. Dolhun

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As taught in, learning resource types, chemistry laboratory techniques.

WARNING NOTICE

The experiments described in these materials are potentially hazardous and require a high level of safety training, special facilities and equipment, and supervision by appropriate individuals. You bear the sole responsibility, liability, and risk for the implementation of such safety procedures and measures. MIT shall have no responsibility, liability, or risk for the content or implementation of any of the material presented.

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This section includes course modules for mastering a series of chemistry laboratory techniques. Information on the original research project assignment and a listing of techniques guides are also provided. All materials may be found in the complete laboratory manual. ( PDF - 2.4MB ) (*Please note: for users on Mac machines experiencing problems viewing the images, downloading and saving the document should resolve this issue.) 

Video instruction tutorials from the Digital Lab Techniques Manual ( DLTM ) are recommended for some of the modules and are noted below.

Introductory Reading Assignment Technique Modules Technique Guides Instrument Operation Guides

Introductory Reading Assignment

Before we get started in the lab on our first class meeting, there are several chapters in the text that you must read first. Our time in the lab will be intense, but of limited duration, so it is important that you complete the readings on time. Not only is the reading essential to your success in 5.301, but it also will help in your development as an experimental chemist.

So, before you begin your experiments, take some time to read over the following chapters in Zubrick & Mohrig. These texts were selected because they’re easy to read and very practical. For more in-depth reading on these and related topics, we recommend the listed selections in the text by Leonard, Lygo, and Procter. It is often difficult to fully grasp a laboratory concept by simply reading about it, but using the strategy of introductory reading, practicing in the lab, and post-lab review reading you will retain most of what we will cover in 5.301.

At the beginning of each lab period, there will be a short overview of that day’s topic, where Dr. Dolhun and your TA will facilitate a discussion of the assigned reading and the actual lab experiment. Much of this time will be set aside to answer questions that you have from the readings.

The following list is the bulk of the reading for the course. There will also be additional reading during IAP, but this introductory reading is meant to familiarize you with the typical chemistry laboratory.

Zubrick, James. The Organic Chem Lab Survival Manual: A Student’s Guide to Techniques. 8th ed. Wiley, 2010. ISBN: 9780470494370. (Chapters 1 - Safety, 2 - Notebooks, 4 - Jointware, 6 - Interesting Equipment, 9 - Clean and Dry, 10 - Drying Agents, 11 - On Products, 15 - Extraction and Washing, 17 - Heat, 18 - Clamps, 27 – TLC, 28 - Column Chromatography, 30 - Gas Chromatography, 32 - Infrared Spectroscopy, 33 – Nuclear Magnetic Resonance 34 - Distillation)

Leonard, J., B. Lygo, and G. Procter. Advanced Practical Organic Chemistry. 2nd ed. CRC Press, 1994. ISBN: 9780748740710. (1 - Introduction, 2 - Safety, 3 - Keeping Records, 4 - Equipping the Lab, 8 - Vacuum Pumps)

Mohrig, J.R., C. Noring Hammond, and Paul F. Schatz. Techniques in Organic Chemistry: Miniscale, Standard Taper Microscale, and Williamson Microscale. 3rd ed. W.H. Freeman, 2010. ISBN: 9781429219563.

(Part 1: Basic Techniques: Chapters 1 thru 16 pages 1-197 Part 3: Spectroscopic Methods: Chapters 20-24 pages 275-438.)

Technique Modules

The technique modules make up the bulk of the class. The modules fall under the topics of “Transfer and Extraction,” “Purification by Crystallization,” “Purification by Distillation,” “Purification by Flash Column Chromatography,” and “Protein Assays and Error Analysis.” It is important to note that the manual does not contain all of the information that you will need to complete these experiments. Some important information will be found in your pre-lab reading, while the rest will be covered during the pre-lab discussion. This three-pronged approach (the texts, the manual, and the discussions) will prepare you to tackle the experiments outlined in the technique modules.

An important part of the modules is the techniques checklist. Each module begins with a list of techniques that you will encounter during the experiment. When you have completed a technique module, you should return to the techniques checklist and check off all of the techniques that you have mastered. If you are still uncomfortable with a specific skill then you should practice it until you feel confident that you could apply it in a different experiment. In addition to various purification and manipulation techniques, this section will also introduce you to spectroscopic techniques like nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, gas chromatography (GC), and ultraviolet-visible (UV-Vis) spectroscopy.

“CC” refers to the “Competent Chemist” modules. “EE” refers to the “Expert Experimentalist” modules.

Transfer and Manipulation (CC)

Acids, Bases & In Between (EE)

Recrystallization—Mothball (CC), and Single Crystal (EE)

Distillation (CC, EE)

Column Chromatography (CC, EE)

Biochemistry (CC, EE)

Original Research Project

Technique Guides

Found in section eight of the Lab Manual, these guides will provide you with step-by-step instructions for some of the more common techniques encountered in a chemistry laboratory.

Instrument Operation Guides

These guides will provide you with step-by-step instructions for some of the instruments commonly encountered in a chemistry laboratory.

Acknowledgements

The laboratory manual and materials for this course were prepared by Katherine J. Franz and Kevin M. Shea with the assistance of Professors Rick L. Danheiser and, and Timothy M. Swager. Materials have been revised by J. Haseltine, Kevin M.Shea, Dr. Sarah A. Tabacco, Dr. Kimberly L. Berkowski, Anne M. (Gorham) Rachupka, and Dr. John J. Dolhun.

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1: Introducing Measurements in the Laboratory (Experiment)

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• Santa Monica College
• To use a metric ruler to measure the dimensions of regular geometric shapes, and to use these measurements to determine the areas of the shapes.
• To measure the volume of a sample of water using a graduated cylinder and a beaker in order to compare their precision.
• To measure the mass of an item using a triple-beam balance and an analytical (electronic) balance in order to compare their precision; also, to determine the mass of a powder by weighing by difference.
• To measure the melting point of an unknown solid and identify it using this measured value.

Our knowledge of chemistry and chemical processes largely depends on our ability to obtain correct information about matter. Often this information is quantitative, in the form of measurements. In this lab, students will be introduced to some common measuring instruments so that they can practice making measurements, and to learn about instrument precision. In Part A of this lab, a metric ruler will be used to measure length in centimeters (cm). In Part B, a beaker and a graduated cylinder will be used to measure liquid volume in milliliters (mL). In Part C, an electronic balance and a triple-beam balance will be to measure mass in grams (g). In Part D, a thermometer will be used to measure temperature in degrees Celsius (°C).

Since all measuring devices are subject to some error, it is impossible to make exact measurements. Scientists record all the digits of a measurement that are known exactly, plus the first one that is uncertain. These digits are collectively referred to as significant digits. Digital instruments, such as an electronic balance, are designed to limit themselves to the correct number of significant digits, and their readings are properly recorded as given. However, when using analog instruments such as rulers and thermometers, the experimentalist is responsible for determining the correct number of significant figures. These instruments are properly read to one place beyond the graduations of the scale.

Example 1.1 : Measuring Length

The ruler markings are every 0.1-centimeter. The correct reading is 1.67 cm. The first 2 digits 1.6 7 are known exactly. The last digit 1.6 7 is uncertain. You may have instead estimated it as 1.68 cm.

Example 1.2 : Measuring the Volume of a Liquid

When measuring liquid volumes, the graduated scale must be read from the lowest point of the curved surface of the liquid – the liquid meniscus.

The graduated cylinder markings are every 1-milliliter. The correct reading is 30.0 mL. The first 2 digits 30 .0 are known exactly. The last digit 30. 0 is uncertain. Even though it is a zero, it is significant and must be recorded.

Example 1.3 : Measuring Temperature

Here, the thermometer markings are every 1-degree. The correct reading is 33.6 °C. The first 2 digits 33 .6 are known exactly. The last digit 33. 6 is uncertain. You may have instead estimated it as 33.5 °C.

Note that the measuring devices used in this lab may have different scale graduations than the ones shown in these examples. Thus, be sure to make it a regular habit to check the scales on all equipment.

When making measurements, it is important to be as accurate and precise as possible. Accuracy is a measure of how close an experimental measurement is to the true, accepted value. Precision refers to the degree of uncertainty in a measurement. For example, a mass measurement of 48.26 g has an uncertainty of ±0.01 g, while a measurement of 48.3 g has an uncertainty of ±0.1 g. Since the measurement of 48.26 g has less uncertainty, it is the more precise measurement. In general, the more decimal places provided by a device, the more precise the measurement will be.

Since measurements are often used in calculations to obtain other values of interest, it is important to consider the number of significant figures that should be recorded for the results of such calculations. If multiplying or dividing measured values, the result should be reported with the lowest number of significant figures used in the calculation. If adding or subtracting measured values, the result should be reported with the lowest number of decimal places used in the calculation.

Example 1.4 : Significant Figures in calculated values

(a) A student runs 18.752 meters in 54.2 seconds. Calculate his average velocity (or speed).

\[velocity = \frac{distance}{time}\]

\[= \frac{18.752 m}{54.2 s}\]

\[= 0.345978 m/s \text{ from calculator}\]

\[= 0.346 m/s \text{ to 3 significant figures}\]

(b) The mass of a glass is measured to be 12.466 grams. If 10.33 grams of water are added to this glass, what is the total combined mass?

\[\text{total mass} = 12.466 g + 10.33 g\]

\[= 22.796 g \text{ from calculator}\]

\[= 22.80 g \text{ to 2 decimal places}\]

The temperature that will be measured in this lab is the melting point of an unknown solid. Melting point is a physical property. When a solid is heated continuously, a point will eventually be reached where it undergoes a physical change and becomes a liquid. The temperature at which liquid first appears is defined as the melting point of that substance. Since all pure substances have unique melting points, a measured melting point can be used to identify an unknown substance by comparing it with a list of known substances and their accepted, true melting points.

The accuracy of a measured value, such as a melting point, may be evaluated by a calculation of percent error. Percent error is a common way of reporting how close a measured experimental value (\(EV\)) is to the true value (\(TV\)):

\[\text{Percent Error} = \frac{| EV − TV |}{TV} \times 100\]

Accurate measurements will typically have low percent errors of <5%.

Materials and Equipment

Metric ruler*, shape sheet, electronic balance, large test tube, 100-mL beaker, 100-mL graduated cylinder, triple-beam balance, 250-mL Erlenmeyer flask, electronic balance, sugar, Bunsen burner, thermometer, 400-mL beaker, stand and ring clamp, small watch glass, wire gauze, capillary tube, latex tubing, scoopula and unknown solids.

In Part D you will be heating a solid powder and several pieces of equipment with an open Bunsen burner flame. Exercise extra caution while using the Bunsen burner, and please remember that the heated items will be very hot to the touch.

Part A: Measuring the Dimensions of Regular Geometric Shapes

• Check out a ruler from the stockroom.
• Obtain a “shape sheet” from your instructor, and then use the ruler to measure the dimensions of the two geometric shapes on it. Measure the length and width of the rectangle, and the diameter of the circle. Record these measurements on your report form.
• When finished, return the ruler to the stockroom.
• Use your measurements to calculate the areas of the assigned geometrical shapes.

\[\text{Area of a rectangle}=l \times w\]

\[\text{Area of a circle} = 2 \pi r\]

(where \(r = \text{radius} = \frac{1}{2} \text{ the diameter}\))

Part B: Measuring the Volume of a Sample of Water

• Obtain a large test tube from your instructor. Fill this test-tube to the brim with tap water, then carefully transfer it to a 100-mL beaker (obtain from your locker). Note that if your 100-mL beaker has no scale markings on it, you will need to take it to the stockroom and swap it for one that does. Measure and record the volume of water in the beaker.
• Again, fill the same test-tube to the brim with tap water, then carefully transfer it to a 100-mL graduated cylinder (obtain from your locker). Measure and record the volume of water in the graduated cylinder. Do these measured volumes have the same number of significant figures?

Part C: Measuring the Mass of Solids

Comparing the Precision of two types of Balances

• Use a triple-beam balance to obtain the mass of a 250-mL Erlenmeyer flask (obtain from your locker).
• Now use an electronic balance to obtain the mass of the same Erlenmeyer flask. Do these measured masses have the same number of significant figures? Be sure to record your measured masses on your report form.

Weighing by Difference

• Using the electronic balance again, obtain the mass of a 100-mL beaker. If you already used this same beaker in Part B, make sure that you carefully dry it before weighing it.
• Add two spoonfuls of sugar to this beaker, using your scoopula. Do not do this over the balance! Then obtain the new combined mass of both the beaker and the sugar. Be sure to use the same electronic balance as before.
• When finished, dispose of the sugar used in the sink.
• Use your two measurements to determine the mass of sugar (only) weighed out.

Part D: Measuring the Melting Point of an Unknown Solid

• Record the ID code of the unknown solid assigned to you and your partner. Powdered samples of the unknown solids are located at the front of lab on the instructor’s lab bench.
• Obtain a capillary tube from your instructor. Press the open end of the capillary tube into the powder. Then turn the tube over and tap the tube lightly against the lab bench to allow the powder to fall into the sealed end. Repeat until you have a depth of about 2-mm of solid in the tube.
• Assemble your equipment as shown in the diagram on page 5.
• Use a large 400-mL beaker half-filled with tap water for the hot water bath.
• Use a small piece of latex tubing like a rubber band to attach the capillary tube to your thermometer. The sealed end should be close to the bulb of the thermometer.
• Place a slotted stopper around the thermometer, and using a clamp, suspend it in the water bath.
• Heat the water bath slowly with your Bunsen burner. The flame should be adjusted to a moderate temperature, with its tip touching the bottom of the beaker. Stir the bath continuously and watch your sample carefully.
• The melting point is the temperature at which liquid first appears. Record your melting point.
• Share your measured value with all other groups who were assigned the same unknown solid as you. You will also need to obtain and record the melting points that they have measured.
• Your unknown solid is one of the substances listed in the table below. Identify your solid by comparing your experimental melting point with the true melting points supplied. Then evaluate the accuracy in your measurement by calculating your percent error.

* This melting point data was obtained from the NIST Standard Reference Database Number 69 ( http://webbook.nist.gov/chemistry/ ). Please note that organic solids actually melt over a range of temperatures. The melting points given in the table represent the lowest temperature in that range, where liquid formation is first observed. Also note that melting points depend on the purity of the solid.

• The unknown sample and the capillary tube (together) should be disposed of in the labeled waste container provided when you are finished.

Pre-laboratory Assignment: Introducing Measurements in the Laboratory

• In Part A of this lab, you will measure the dimensions (length, width, diameter) of several geometric shapes.
• Using a ruler, you measure the length of a rectangle to be 12.75 cm and the width to be 3.64 cm. Calculate the area of this rectangle (show work), reporting your answer to the correct number of significant figures.
• What is the formula for the area of a circle?
• In Part B of this lab, you will measure the volume of a sample of water, in milliliters (mL).
• What two measuring instruments will you use to measure the water volume?
• Consider the following two volume measurements: 57.7 mL and 57.68 mL. Which of these is the more precise measurement, and why?
• In Part C of this lab, you will measure the mass of several different items, in grams (g).
• What are the two types of balances you will use to measure mass?
• An empty beaker has a measured mass of 29.456 g. When some salt is added to the beaker, the combined mass is 36.176 grams. Calculate the mass of the salt only (show work), reporting your answer to the correct number of significant figures.
• In Part D of this lab, you will measure the melting point of an unknown solid, in degrees Celsius (°C).
• Define “melting point".
• Is melting point a physical or chemical property of matter?
• A student measures the melting point of an unknown compound to be 53.5 °C. She later discovers that the compound is chlorothymol, with a true melting point of 58.8 °C. Calculate her percent error (show work) to the correct number of significant figures. The required formula is on page 3 of the Procedure document.
• You will use a variety of equipment to measure the melting point of the solid. Sketch a set-up of the equipment on the back of this page, and label all items in your sketch.

Lab Report: Introducing Measurements in the Laboratory

Experimental Data

Data Analysis

• Perform the conversions indicated below. Show your work, and report your answers in scientific notation.
• Convert the measured rectangle length to pm.
• Convert the measured circle diameter to km.
• Calculate the areas of your rectangle and circle in cm 2 . Show your work, and report your answers to the correct number of significant figures.
• Area of rectangle
• Area of circle
• Convert the area of your circle to μm 2 . Show your work, and report your answer in scientific notation.
• Compare your volume measurements in the table above. Which instrument, the beaker or the graduated cylinder, provides the more precise measurement? Explain.
• Convert the volume of water obtained using the graduated cylinder to hm 3 . Show your work, and report your answer in scientific notation.

Table 1 – Mass of an Erlenmeyer Flask

Table 2 – Weighing by Difference

• Compare your mass measurements obtained for the Erlenmeyer flask in Table 1. Which balance, triple-beam or electronic, provides the more precise measurement? Explain.
• Consider the data you obtained in Table 2.
• Calculate the mass of sugar weighed out. Show your work.
• Circle one: When performing the above calculation, significant figures / decimal places are the primary consideration.
• Convert the mass of the sugar weighed out to fg.
• Convert the mass of the sugar weighed out to Gg.

Unknown Compound ID Code:

• Using the average value above, identify your unknown compound (see Procedure, Part D, #7).
• Name of Compound:
• True Melting Point:
• Which of the measured melting points recorded in the table was the most accurate? Explain.
• Calculate the percent error between the experimental melting point that you and your partner measured and the substance’s true melting point. Report your answer to the correct number of significant figures.
• Perform the temperature conversions indicated below. Show your work, and report your answers to the correct number of significant figures.
• Convert the true melting point of your compound to K.
• Convert the true melting point of your compound to °F.

CHE 210 - General Chemistry I (Lab) - Textbook

Attribution.

• LAB 2 (Week 3) The Density of Liquids and Solids
• LAB 3 (Week 4) Nomenclature of Ionic Compounds
• LAB 4 (Week 5) Chemical Formlua Determination
• LAB 5 (Week 6) Types of Reactions
• LAB 6 (Week 7) Mole Ratios and Reaction Stoichiometry
• LAB 7 (Weeks 8 & 9) Titration of Vinegar
• LAB 8 (Week 10) Calorimetry and Hess’s Law
• LAB 9 (Week 11) Determination of the Gas Constant
• LAB 10 (Week 12) Gravimetric Analysis of an Unknown Sulfate
• LAB 11 (Weeks 13 & 14) Spectrochemistry

Attribution & Licensing

Chem 210 general chemistry 1.

Compiled by Nelson Nunez-Rodriguez   

Conditions of Use:

Click on the links below for Lab 1, Introducing Measurements in the Laboratory and the Excel Assignments:

• Introducing Measurements in the Laboratory
• Prelab Assignment: Introducing Measurements in the Laboratory
• Lab Report: Introducing Measurements in the Laboratory
• Excel Assignment
• Prelab: Excel Assignment
• Report: Excel Assignment

Introducing Measurements in the Laboratory,  Online Chemistry Lab Manual.   Authored by:   Physical Sciences Department,  Santa Monica College.  Located at:  https://drive.google.com/file/d/1PsK5x5CbThyFHK27CfTogoUxmoGlLuaD/view?usp=sharing   Attribution:  CC BY-NC 4.0

Prelab Assignment: Introducing Measurements in the Laboratory,  Online Chemistry Lab Manual.   Authored by:   Physical Sciences Department,  Santa Monica College.  Located at:  https://drive.google.com/file/d/1yOoVcC1n8L9K2JjsMQgwG63-rGTr9TAb/view   Attribution:  CC BY-NC 4.0

Lab Report: Introducing Measurements in the Laboratory,  Online Chemistry Lab Manual.   Authored by:   Physical Sciences Department,  Santa Monica College.  Located at:   https://drive.google.com/file/d/1Y2wv7Z59jk9YjTjc6TF1I2jKUT90tomr/view   Attribution:  CC BY-NC 4.0

Excel Lab Assignment, CHE 210, Lab 1, Week 2. Authored by:  Van Phan Chan.  Provided by: Hostos Community College.  Located at:  https://docs.google.com/document/d/1CdQnHmvcARQrRpKZW2LbYQcC0ssx7N1V/edit?usp=sharing&ouid=113518982236079209444&rtpof=true&sd=true   License:   CC BY-NC 4.0

Excel Tutorial: Pre-Lab Assignment, CHE 210, Lab 1, Week 2. Authored by:  Van Phan Chan.  Provided by: Hostos Community College.  Located at:  https://docs.google.com/document/d/1Ci6D6TY3x1druWcu-XyKKmixc3HNQfyZ/edit?usp=drive_link&ouid=113518982236079209444&rtpof=true&sd=true   License:   CC BY-NC 4.0

Excel Report Sheet, CHE 210, Lab 1, Week 2. Authored by:  Van Phan Chan.  Provided by:  Hostos Community College.  Located at:   https://docs.google.com/document/d/1CkzCmUHSAvxqBfJUQtdGK1fOoFZRSqc0/edit?usp=drive_link&ouid=113518982236079209444&rtpof=true&sd=true   License:   CC BY-NC 4.0

Physical Sciences Department,  Santa Monica College. Chem 10 Lab - Instructions:  https://sites.google.com/view/smcchemistry/chemistry/chem-10-experiments?authuser=0

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• Last Updated: Dec 29, 2023 12:09 PM
• URL: https://guides.hostos.cuny.edu/chem210

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