Experiment 1: Lab Notebooks. Measurement and Significant Digits This exercise will demonstrate how to make proper measurements in a laboratory. You will also learn how to record observations and measurements correctly in a laboratory notebook.

1.1 Keeping a Lab Notebook The scientific method is the process by which experimentalists learn the basic principles of science. It includes the following steps: 1. Ask a question 2. Form a hypothesis to answer the question 3. Perform an experiment to test your hypothesis 4. Analyze your data and observations to confirm or disprove your hypothesis 5. Communicate your results For most of your laboratory experiences in this course, your job is to do an experiment, interpret your data and draw conclusions. However, in order to analyze your data and draw a conclusion, you must take good notes on what you observe during the experiment. Typically, scientists keep a laboratory notebook to record their ideas, experimental procedures, data, observations, and conclusions. The notebook is designed to be a permanent record. Therefore, it should have the following characteristics: 1. It should be a permanently-bound book or a spiral bound book with pre-numbered pages so that pages cannot be removed. 2. Pages should be numbered consecutively. 3. No pages should be skipped, even if you start a new project in the middle of doing another one. (Simply put “Go to page ...” at the end of an entry if that work is continued somewhere else in the notebook.) 4. It should have a table of contents at the beginning. 5. All entries should be made in ink. 6. All work should be dated. 7. Any mistakes should simply have a line drawn through them so that they are still readable. Entries should never be obliterated so that they can’t be read. CHEM 139 Lab Guide

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It’s so important to properly record all your notes that some industries that deal with proprietary work even require each page to be signed and dated by the person that made the entry and then witnessed by another person. Additional Guidelines for CHEM 139 Lab Notebooks 1. Fill in all of the information requested on the inside cover of your lab notebook. This will be useful if you ever misplace your notebook or need to contact your lab instructor or lab partner. In an industrial or research setting it will prevent others from taking credit for your work. 2. Keep the table of contents up to date by entering the number, title and pages of each experiment. 3. You will record all of your data and observations in pen on the white pages of the notebook. A copy of what is written on the white page will be created on the yellow page beneath. Two important things to remember: A. Place the page protector after the yellow page in order to protect the other pages from being marked by your writing. B. Keep the original (white) pages in your notebook. This is your permanent record. When you leave lab, the YELLOW pages should be turned in to your lab instructor. In an industrial or research setting, the yellow pages may be kept in a safe as a back-up in case of accidental damage to the original notebook. 4. Fill in all of the information at the top of the page (Date, Lab Partner, Experiment Name and Number, etc.). USE PEN Be sure to record the correct section number. 5. Create a section beneath the title called “Objective.” (This section is also sometimes labeled as the purpose or introduction.) In this section, describe what the objective of the experiment is. This section should typically be 1 – 3 sentences long. (Hint: Look at the first paragraph of the lab manual experiment for clues on what to write.) If the goal of the experiment is to perform a specific chemical reaction, you should write out the reaction under the objective. 6. Create a section entitled “Procedure.” Your Lab Guide contains all of the details of the procedure so start by referencing the lab handout. A statement such as: “Reference CHEM 139 Experiment 1 Lab Guide.” As you go through the experiment you should record what you did for each step. You will not need to record as much detail as the Lab Guide provides, but you should be specific about what you did. You need to record enough information so that you can look back at your notebook and know what you did. For example, the Lab Guide for this experiment describes in detail how to read the volume in a graduated cylinder (looking at eye level, reading the bottom of the meniscus, etc.). For your notebook entry you would simply record: “Read the volume in graduated cylinder A.” CHEM 139 Lab Guide

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Note that your lab notebook pages are divided in half vertically. One convenient method for organizing the notebook is to label the left column “Procedure” and label the right column “Data and Observations” (see below). 7. Next, create a section entitled “Data and Observations.” In this section you should record ALL observations and data (measurements). Be specific about your observations and what you were doing (procedure) when the observation was made. When in doubt, write something down. It’s always better to write too much information than too little! It is imperative that you record the observations as they occur. Don’t try to go back later and remember what happened. Nor should you rely on your lab partner to record the observations so that you can copy them later. Take time while performing the experiment for each person to stop and write down observations. Likewise, all measurements (your data) should be recorded directly into your lab notebook and all data should include the units in which the measurement was made. For example, when you go to the balance to mass something BRING YOUR NOTEBOOK WITH YOU and record the mass directly into your notebook. 8. For most experiments you should have a section for calculations. You should show your work for at least one sample calculation and then compile the rest of your results into a table. 9. Lastly, you should have a section entitled “Conclusion.” This should be a few sentences that sum up your results. You may not always have time to complete this section while in lab.

1.2 Measurements 1.2.1 Types of Measurements and Their Units Each kind of measurement you make has a certain name such as length, volume or mass. These kinds of measurements can be reported in several ways depending on what unit you use. For example, if you measured the length of a marathon, you’d find it is 26.2 miles or 42.2 kilometers. In this example length is the kind of measurement and miles and kilometers are units. Whenever you make a measurement, you must always report what units you’ve used to make your measurement. A list of different types of measurements and examples of associated units (and their abbreviations) are given in Table 1.1. Type of Measurement Length (l) Mass (m) Volume (V) Temperature (T) Time (t)

Units inch (in), centimeter (cm), kilometer (km) gram (g), kilogram (kg) gallon (gal), liter (L), cubic centimeter (cm3) Fahrenheit (◦F) second (s), minute (min)

Table 1.1: A list of types of measurements with examples of associated units. CHEM 139 Lab Guide

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1.2.2 Making Measurements and Reporting Significant Figures When making a measurement, you must report the proper number of significant figures. Significant figures indicate the resolution of the instrument used to make a measurement. Resolution is the ability to distinguish one value from another on an instrument or measuring device. You should estimate the value between the smallest divisions on your measuring device whenever possible. Look at the example in Figure 1.1.

Figure 1.1: Measuring length with a ruler. In the first picture, the ruler only marks the “ones” place, so we must estimate the digit between the lines which is in the “tenths” place. Since the line is slightly past the 6 cm mark, we would report the length of the line as 6.2 cm. In the second picture, the ruler has a mark every tenth of a centimeter and it looks like the line is exactly at the 6.3 cm mark. We must estimate to the “hundredths” place, so we report the length of the line as 6.30 cm. Measuring Length 1. In your lab kit, you will find part of a pipe cleaner. Use the ruler provided to measure the length of the pipe cleaner in centimeters and record this value in your lab notebook. Be sure to include units and the correct number of significant figures. Convert this length measurement to millimeters. Clearly show your work in your lab notebook. Measuring Volume In Figure 1.2, a graduated cylinder has been used to measure the volume of a liquid in milliliters. Notice that the surface of the liquid is slightly bowed. This is called the meniscus. For liquids, volume should always be determined from the bottom of the meniscus at eye level, CHEM 139 Lab Guide

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as shown. Also, notice that the reported volume is 17.0 mL. Here we have estimated one more decimal place past what we can read off the cylinder. It just so happens that that digit is zero in this case. We report it nonetheless.

Figure 1.2: How to measure volume with a graduated cylinder. 2. At the front of the laboratory, there are three different sized graduated cylinders labeled A, B, and C. Measure the amount of water in each cylinder, and record your answer in your lab notebook. Remember to use the correct number of significant figures and appropriate units. Convert the volume in cylinder A to liters. Clearly show your work in your lab notebook.

1.2.3 Resolution of Measuring Devices There are many different pieces of glassware that can be used to measure volume. Several examples are shown in Figure 1.3. However, certain devices have a higher resolution than others. Glassware with higher resolution will measure volumes with a higher number of significant figures and therefore greater precision. In the prelab assignment you were asked to determine which of the four pieces of glassware in Figure 1.3 is the most precise. Now we will compare the precision of the beaker to the precision of the graduated cylinder experimentally.

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Figure 1.3: Examples of glassware used to measure volume. 3. At your station you have a small bottle of colored water. Pour the entire contents of the bottle into your beaker. Use the markings on the beaker to measure the volume of the water. Record this measurement in your lab notebook. Remember to use the correct number of significant figures and appropriate units. 4. Transfer the water from the beaker to a dry 50 mL graduated cylinder. Now, mea- sure the volume of water in the graduated cylinder and record this measurement in your lab notebook. Remember to use the correct number of significant figures and appropriate units. 5. Based on the number of significant figures in the previous two answers, you should be able to tell which device has higher precision, the beaker or the graduated cylinder. Which is it? (Record your analysis in your notebook. Use complete sentences to explain your reasoning.) In all sciences, it is important to quantitatively report your results whenever possible. That means you must provide a number if you can. To quantitatively describe the difference between two numbers, you would calculate the percent difference. The percent difference is a way to numerically report how far apart two numbers are from one another and is calculated from the formula below: difference between two values X 100= % difference the value you're comparing the number to For example, you find a sweater that’s on sale for $40 when it normally costs $50. To find the percent difference from the normal price, you would take the absolute value of the difference in price divided by the price you’re comparing the sale price to (that’s the original price) and multiply that value by 100. In this example, the percent difference would be 20%. 6. Following this same principle, you should calculate the percent difference in the measured volumes from the beaker and the graduated cylinder using the formula below and enter CHEM 139 Lab Guide

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the answer in your notebook. difference between measurements × 100 = % difference most precise measurement

1.4 Hazardous Waste and Clean-up 1.4.1 Hazardous Waste There is no hazardous waste generated in this lab. You can pour the water you used down the drain.

1.4.2 Clean-up Dry your glassware and return it to your station. Then, wipe down your benchtop with a wet paper towel and dry it. Have your instructor check your station before your leave. Once your lab station has been inspected, ask your lab instructor to sign your notebook. BEFORE YOU LEAVE LAB: Tear out the carbon-copy pages (the YELLOW pages) of your notebook. Make sure your name, your partner’s name and your section number are on each page. Staple these pages together and turn them in to your instructor.

1.4.3 Assignment Enter all of your data, calculations and answers to questions in the Lab 1 Assignment in Chem21. You will need to refer to your notebook for this. The Assignment is due at 8 AM on the day of your next lab meeting.

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