Lab 2 Laboratory Measurment Fall 2023_updated

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Dec 6, 2023

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Lab 2: Laboratory Measurements Purpose: This lab's purpose is for you to learn how to use different laboratory equipment and to assess the precision and accuracy of volume measuring devices. This lab will help you practice the following skills: 1. Demonstrating the proper use of common laboratory equipment (balances, weigh boats, graduated cylinder, centrifuge tubes, glass test tubes and pipettes) to measure, contain, and dispense mass and volume. 2. Making serial dilutions of a solution. This assignment will help you gain the following knowledge: 1. Recognizing metric units of measure and apply these units to measuring techniques for determining mass and volume. 2. Identify the difference between accuracy and precision. 3. Understanding how to use scientific notation. Introduction The laboratory activities you will do today are important for several subsequent laboratory activities for this course . For example, you will need these skills when making NaCl solutions for the brine shrimp labs (weeks 5 and 6) and when preparing reaction mixtures for the enzyme labs (weeks 8, 9 and 10). For both the brine shrimp and enzyme labs you will be performing experiments that require accurate and precise measurements. These results will be included in a scientific write-up that is in the form of a scientific poster (worth approximately 40% of your great, in total) The ability to use these measuring devices is also a skill that will help students that plan to work in a laboratory setting. 1

I. Basic Measuring Techniques Many experiments, including the ones you read about in the published article on Artemia , require accurate and precise measurement of samples and liquids. Accuracy and Precision – what does this mean? Measurements should be both precise and accurate . What do these two words mean? Accuracy is the degree to which an observed value corresponds to a true value. Precision is the degree to which measurement are reproducible when repeated. A measurement may be accurate but not precise; or precise but not accurate; both precise and accurate; or neither precise nor accurate (see the image below). Lack of precision or accuracy may be a result of the measuring device (e.g., something internal or perhaps a calibration error) or improper use and technique when performing the measurements. In today’s lab you will get practice testing your ability to use the measurement devices and assessing your accuracy and precision. 2

Measuring volumes: Serological pipets (image A) are much more accurate than other larger measuring devices such as the graduated cylinder. They are generally used when measuring volumes between 1 mL and 25 ml. You must be able to correctly read the scale on a serological pipette to measure the desired volume. A pipet aid is a mechanical device used to draw liquids into the serological pipet. You will be given a manual pipette filler like the one shown in the image B. These can be used with all size serological pipettes (1 ml, 5 ml, and 10 ml). A. B. Using a serological pipet (1 pt total) 1. Pick up the 10 ml serological pipet. (0.25 pts) What is the maximum volume that this pipet can measure? 10 ml (0.25 pts) What volume do each of the lines (graduations) on the pipet represent? 0.1 ml or 100  l 2. Pick up the 1 ml serological pipet. (0.25 pts) What is the maximum volume that this pipet can measure? 1 ml (0.25 pts) What volume do each of the lines (graduations) on the pipet represent? 0.01 ml 3. Did you notice that the front and the back of the serological pipet look different? (0.5 pts) Why do you think this is? Depending on whether you’re pulling liquid in or delivering it. 3

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Micropipettes (image C) are used to deliver micro volumes aseptically and accurately. Common ranges are 1- 10 µl; 10-100 µl; and 100-1000 µl. Several brands of micropipettes are on the market. While each has some unique design features, all have certain common features. C. Common features of a micropipette: • Each is designed to work with a disposable tip into which the liquid to be measured is drawn. • Each has a mechanism for dialing in the desired volume. • Each has a multiple stop plunger: the first stop is calibrated to pick up the volume that has been dialed in; the second stop is designed to deliver the entire volume of air behind the liquid to ensure complete delivery of the liquid volume. • Tips are usually color-coded for the size of the pipette and come packaged in boxes for easy insertion onto the micropipette. 4

Using a micropipette: ALWAYS USE A TIP WITH YOUR MICROPIPETTES NEVER SET A PIPET ABOVE OR BELOW ITS LIMIT (For example, never set a p-1000 micropipette lower than 100  l or higher than 1000  l) CHANGE THE TIPE BETWEEN DIFFERENT LIQUIDS TO AVOID CONTAMINATING YOUR SAMPLE 1. Pick up a micropipette and review the parts of the tool. Locate the plunger button (push button), tip ejector button, volume adjuster (thumbwheel), volume display window, and where the tip is loaded. 2. The display window shows the volume the micropipette will load and dispense. By turning the thumbwheel, practice setting the micropipette to the following volumes in the image below. D. 5

Measurement conversion: Several times during this course you will need to convert milliliters (ml) to microliters (  l), milligrams (mg) to grams (g) and vice versa. Let’s practice how to do this. To convert ml to  l, multiply the number of milliliters by a thousand.  l = ml × 1000 (0.25 pts) How many  l is there in 5.6 ml? 5600 µl To convert  l to ml, you need to divide the number of microliters by a thousand. ml =  l / 1000 (0.25 pts) How many ml is there in 56.0  l? 0.056 ml A similar conversion can be done for mg and g To convert g to mg, multiply the mg by a thousand. To convert mg to g, divide the mg by a thousand. Measuring volume and checking accuracy by measuring mass You will measure volumes using a micropipette, and then you will measure the same volumes using a serological pipette. You will determine how well you perform pipetting, using each instrument, by weighing the volumes of the liquid being pipetted on a scale. Note that 1 ml of H20 is defined to have a mass of 1 g at standard temperature and pressure conditions. Before you start, examine the 1000  l micropipette and the 5 ml serological pipette. Based on your examination: (0.5 pts) Predict which device you expect to be more accurate? Explain why you predicted this. I predict the micropipette to be more accurate because the machine measures a specific amount but with the serological pipette, you’re measuring it yourself and it’s more vulnerable to human error. 6

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Begin the procedure: 1. Using the micropipette at your bench, insert a tip onto the micropipette. Slowly depress the plunger with your thumb until you feel the first stop point. Apply more pressure to depress the plunger and feel the second stop. If your micropipette does not have a separate mechanism for tip removal, apply more pressure and note the ejection of the tip. Ask your lab instructor to demonstrate how to use a micropipette or to confirm that you are using it correctly. 2. Place a clean and dry weigh boat on the balance pan and tare the balance. 3. Take your 100 µl volume micropipette and set the volume for 100µl. Place an appropriate tip on the micropipette. a. Using the 100 µl micropipette, pipette up 100 µl of water and dispense it into the weigh boat. Record the weight in the table below. Since the density of water is 1.00 g/ml at room temperature, we expect 100 µl (which is the same as 0.1 ml) to weigh 0.1 g, or 100 mg. DO NOT POUR OUT THE WATER! Leave the weigh boat on the balance. b. Next add 500 µl of water to the same weigh boat using the appropriate micropipette (100 – 1000 µl capacity). Note that your total volume is now 600 ul. Record the expected weight of 600 ul of water in the table below. Now weigh the microcentrifuge tube and record the measured weight in the table below. DO NOT POUR OUT THE WATER! Leave the weigh boat on the balance. c. Finally, add 1000 µl to the same weigh boat so that your final volume is approximately 1600µl. Record the expected weight of 1600 ul of water in the table below. 4. Now take a second weigh boat and tare the balance . Do not use the same weigh boat you were using for steps 1 – 3. a. Using a 5.0 ml serological pipette, pipette up 0.1 ml of water and dispense it into the weigh boat. Record the predicted weight of 0.1 ml water, and record the measured weight, in the table below. DO NOT POUR OUT THE WATER! b. Next use the same 5.0 ml serological pipette to add 0.5 ml of water to the same weigh boat . Record the predicted weight of the total volume of the water in the weigh boat, and record the measured weight, in the table below. DO NOT POUR OUT THE WATER! Leave the weigh boat on the balance. c. Finally, use the same 5.0 ml serological pipette to add 1.0 ml to the same weigh boat . Record the predicted weight of the total volume of the water in the weigh boat, and record the measured weight, in the table below. 7

Data Table I: Volume of H 2 O Pipetted Volume Total Predicted Weight Observed/Measu red Weight (in mg) First: micropipette 100 µl 100 µl 100 mg 100 mg + 500 µl 600 µl (100 + 500 µl) 600 mg 580 mg + 1000 µl 1600 µl 1600 mg 1570 mg Second: serological pipette 0.1 ml 0.1 ml 100 mg 70mg + 0.5 ml 0.6 ml 600 mg 510mg + 1.0 ml 1.6 ml 1600 mg 1400mg (0.25 pts) Does your data indicate that one of the volume devices was more accurate? Does this agree with your prediction? Offer an explanation in either case. Yes the micropipette was more accurate. It supports my prediction because the measurements were closer to the prediction with the micropipette than the serological. (0.25 pts) How would you determine which device was more precise? The device which has more accurate and closer measurements to the predicted measurements Precision of measurements using a micropipette. How precise are you when using a micropipette? In the table below, record the results obtained by you and your lab partner (each table worth 2 points; 4 points total)

Person 1 ( emma): Set the appropriate micropipette to 560 ul and measure 4 times. Record the volumes in the table. Measurement # Volume 1 560mg 2 550mg 3 560mg 4 550mg Person 2 ( name): Set the appropriate micropipette to 730 ul and measure 4 times. Record the volumes in the table. Measurement # Volume 1 730mg 2 730mg 3 720mg 4 720mg Where your measurements precise? Explain why or why not. Our measurements were precise because they were all close together. Significant Figures and Scientific Notation When measuring mass, length, or volume of objects, scientists may elect to write the number in scientific notation . A number is expressed in scientific notation when it is written as a product of a decimal number between 1 and 9 and the number 10 raised to the proper power. For example: 1000 = 1 x 10 3 568,000,000,000 = 5.68 x 10 11 0.00000044 = 4.4 x 10 -7 When converting a number that is larger than 10 into scientific notation, the decimal point must be moved left. When the decimal point is moved left, the exponent on the 10 is positive and equal to the number of decimal places moved. When the number is smaller than 1, the decimal point must be moved right, and the exponent on the 10 is negative and equal to the number of decimal places moved. Students often ask how many decimal places a given measurement can include. Numbers that are experimentally measured are not exact because of small errors or uncertainties associated with the laboratory measurement. Scientists indicate these uncertainties by using an appropriate number of significant digits. A significant digit is one whose value is reasonably reliable. This is accomplished by

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recording all digits that are known with certainty, and then adding one additional digit that has uncertainty (e.g., is estimated by the observer). In other words, report digits that can be clearly determined with the measuring device. Usually this will give a value that includes digits whose certainty is known (e.g., is marked or indicated on the device) and one estimated digit. When you are using a brand-new instrument, you need to determine the actual precision of the instrument, regardless of how many places are shown on the instrument’s output . You are writing a scientific paper and must use scientific notation in the materials and methods section. You need to provide the volume of a solution used in one of your experiments. (0.5 pts) The volume used was 1,250  l. Keeping this volume in  l units, how would you use scientific notation to rewrite this volume? 1.25 x 10 ^3 (0.5 pts ) You also used 0.0065 g of salt to make your solution. Keeping this mass in g units, how would you use scientific notation to rewrite this mass? 6.5 x 10^-3 Practice with measurements by performing serial dilution In this lab we will introduce you to making a serial dilution of a solution. This method will come in handy for future labs, when making solutions of different concentrations. Some terms defined (from biologyonline.com):  Solution – a type of homogenous mixture in which the particles of one or more substances (the solute) are distributed uniformly throughout another substance (the solvent). A typical example of a solution is sugar dissolved in water: sugar is the solute and water are the solvent.  Solute – a component of a solution: a substance (usually in lesser amount) dissolved in another substance  Solvent - A liquid in which substances (or solutes) are dissolved forming a solution. In a solution, the solvent is usually present in greater amount than the solute.  Concentration - The measure of the amount of a substance (solute) in a solution. The ratio of the mass or volume of a substance (solute) to the mass or volume of a solvent or solution Concentration is usually written with the solute's mass over the solvent's volume.

For example, concentration = 5 mg/ 1ml  Dilution - the action of making a liquid more dilute; the action of making something weaker in force, content, or value  Serial Dilution - a stepwise dilution of a substance in solution. Usually, the dilution factor at each step is constant. Making a serial dilution 1. Obtain a 15 ml tube and fill it with 10 ml of water. 2. Add 2 drops of food coloring and mix well. 3. Obtain 4 tubes. 4. In the first test tube transfer 4 ml of the colored water. 5. In a second test tube, transfer 2ml of the colored water from test tube 1. 6. Add 2ml of water to the second test tube. 7. Place the cap on the top of test tube 2 and invert the tube to mix. 8. In a third test tube, transfer 2 ml of the colored water in test tube 2. 9. Add 2ml of water to the third test tube. 10. Place the cap on the top of test tube 3 and invert the tube to mix. 11. In a fourth test tube, transfer 2 ml of the colored water in test tube 3. 12. Add 2 ml of water to the fourth test tube. 13. Place the cap on the top of test tube 4 and invert to mix. 14. You’ve now made a serial dilution of a solution. (1 pt) In your own words describe how you made the serial dilutions: We put 10ml of water in the first tube and 2ml of water in each tube after and we would take 2ml from the first tube and deliver it to the next and then do the same so on. (1 pt) Explain what happened to the solution due to the serial dilutions. It became more diluted by water and the food coloring became more faded. And the end solution was halved three times and went from 0.2 ml to 0.025ml.

Related Questions

How will each of the following experimental errors influence the results of your calculated densities you reported? State whether the error will tend to make your density results too large, too small or unchanged. Explain why this would occur by identifying which measurements would be affected (high or low) and how this would affect the calculated density. Use the followingIn method 2, the metal cylinder you used had a number of air bubbles on its when immersed in the water

3. Plot the mass and volume data in your Data Table 1 to graphically determine the density of water using total mass (on the y-axis, in grams) vs. total volume (on the x- axis, in milliliters). You may elect to complete this graph by hand using the graph paper provided, or using a graphing program such as Microsoft Excel. Draw one "best fit" straight line through all your plotted points. Make sure to label both axes, and properly title the graph. Calculate slope of the line (Show actual calculations directly on graph, and clearly label the two points on the line used for your slope calculation) slope =______ The density of water as determined graphically is: _g/mL (Since the slope of the line indicates change in mass over change in volume, the slope of your line is the density of the water.)

4. When you get your 5th correct answer, you will get a certificate that you can share with your teacher letting your teacher know how you did. Please provide a screenshot of your certificate showing you got this completed. DATA Part B: Measuring the Mass of Materials Top Loading Balance Mass Empty Beaker (g) Mass of Beaker + Paper Clips (g) Mass of Paper Clips (g) Analytical Balance Mass of Empty Beaker (g) Mass of Beaker + Paper Clips (g) Mass of Paper Clips (g) DATA ANALYSIS: 1. Show your calculation for the mass of paper clips using the top-loading and analytical balances. 2. Which of the balances, top-loading or analytical, has the most uncertainty per measurement? Explain. Page 10 of 14

Review Question 4)

Kindly help me with this please.

What are replicates in Analytical Chemistry? O The component of a sample that repeats over different assays. Similar assays done to different samples A sample that contains exactly the same amount of analytes than the original sample similar samples that are analyzed at the same time and in the same way

4. Describe at least three systematic errors that might occur while weighing a solid on an analytical balance.

Use the lab introduction to answer the following question. When answering this problem, report the answer with the appropriate number of significant figures. When entering units, use proper abbreviated units with proper capitalization. A beverage drink mix sample is prepared by mixing a packet of beverage powder in a gallon (3.78 L) of water. A sample for analysis is prepared by diluting 10.00 mL of this solution in a 50.0 mL volumetric flask. When measured using a colorimeter, this diluted solution has an absorbance of (3.4900x10^-1). The calibration curve for the experiment yielded a linear fit of y = (2.240x10^4)x+ (1.22x10^-2) and an R2 value of 0.9911. Determine the molar concentration of food dye in the analyzed sample.

Why is it inappropriate to report yields with decimal-place accuracy (as opposed to whole numbers)?

Please answer question number 2 correctly with the correct answer. there is a picture of an example of a ''Dimensional analysis Format' below. please write out all work showing the math in dimensional analysis format. (please show all work) Question 3: What is the molar mass of each of the following compounds? A. C6H12O6 B. NaHCO3

Part a through c please a) You are presented with 12.0 kilograms (kg) of sugar for a rum brewing project. The rum recipe calls for ounces (oz) of sugar. How many ounces of sugar are in 12.0 kg? Remember: 1 kg = 1000 grams (g); 453.6 g = 1 pound (lb) [approximately]; 16 oz = 1 lba) 87.0 ozb) 192. ozc) 423. ozd) 768. oz b) A graduated cylinder contains 95.1 mL of a liquid. The mass of the graduated cylinder with the liquid is 140.000 grams. The mass of the graduated cylinder when empty is 44.900 grams. The liquid contained in the cylinder is most likely:a) ethyl alcoholb) waterc) corn oild) chloroform c) A beaker’s mass is 21.05 g, and the mass of this beaker containing a sample of water is 22.150 g. The mass of the water in the beaker is,a) 1. gb) 1.1 gc) 1.10 gd) 1.100 g