Experiment 1: Determination of Density

GRADING RUBRIC EXPERIMENT 1 – LAB REPORT Worksheet (80 pts) Student name: __ TA name: _ Day & time of the lab: _02/01/2022 _9AM-1PM_____________________ The lab report packet for this experiment should consist of the following in THIS ORDER: The lab report packet for this experiment should consist of the following: 1. (10 pts) IN-lab notebook pages 1.1. Experimental procedure 1.2. Observations that were noted 2. (70 pts) The WORKSHEET 2.1. (60 pts) Complete (full sentence) answers to ALL the discussion questions (DQ) and Data Analysis Section. 2.2. (10 pts) POST-lab notebook pages 2.2.1. All calculations performed present Complete this worksheet and turn in your digital lab packet to Canvas. Feel free to adjust space in this document as needed. The tables provided here are only an example of these may look like, feel free to replace the entire tables with your own creations using Excel, etc All tables and figures (graphs) must be accompanied by captions which should be positioned above tables and below figures. TURN IN the digital copy to Canvas on the due date by 11:59 pm. All electronic material must be completed by the due date to avoid late penalties. P. Sotelo SP2022 1 IN-LAB NOTEBOOK PAGES (10 pts) Name, date, title of experiment, detailed procedure and observations taken while in lab. DISCUSSION QUESTIONS & POST-lab analysis of data - (70 pts) All discussion questions must be answered in complete sentences. Complete the tables 1&2 below. You may use Excel to perform all the calculations but do show the following “sample calculations” in your notebook in the POST-lab P. Sotelo SP2022 2 section (immediately following the IN-lab notes). You must ALWAYS show all the work and the calculation leading to the result in detail for full credit. (8 pts) DQ1. You used a beaker, a graduated cylinder and a volumetric pipette to transfer 5 mL of a liquid sample into a small beaker. What exact volume did you measure? (Hint: How many significant figures or decimal places do your measurements have for each type of glassware? Was it 5.0 mL or 5.00 mL or else?) Is this information available on the glassware itself? If yes, where and what did you notice? And finally, which one of the glassware used in this experiment give you a more accurate measurement? After using a beaker, a graduated cylinder, and a volumetric pipette to transfer 5 mL of a liquid to a small beaker, I recorded 5.0 mL, 5.00 mL, and 5.000 mL. The number of decimal places and significant figures I round to for a specific glassware is dependent on the accuracy of that specific equipment. Thus, because a beaker is least accurate, only one decimal place behind the decimal point is given, while three is given for a volumetric pipette and two for a graduated cylinder. Moreover, to determine the amount of decimal places when the meniscus in between two numbers is determined by the number of decimal places for the glassware, as said before, which will indicate which decimal point is the estimate number. The glassware that was used in this experiment that is the most accurate measurement is the volumetric pipette, which is why there are three numbers behind the decimal point. (10 pts) Table 1: A sample table summarizing all measurements leading to the density of water. Water 30 mL beaker Trial 1 P. Sotelo SP2022 Empty beaker (g) 21.000 g Beaker + water (g) 23.993 g 3 Mass of water (g) 2.992 g Density (g/mL) .6 g/mL Trial 2 Trial 3 Graduated Cylinder Trial 1 Trial 2 Trial 3 Volumetric Pipette Trial 1 Trail 2 Trial 3 21.000 g 20.998 g Empty beaker (g) 24.183 g 24.121 g Beaker + water (g) 3.183 g 3.123 g Mass of water (g) .6 g/mL .6 g/mL Density (g/mL) 20.993 g 25.539 g 4.546 g .91 g/mL 20.996 g 25.329 g 4.333 g .87 g/mL 20.995 g 25.556 g 4.561 g .91 g/mL Empty beaker (g) Beaker + water (g) Mass of water (g) Density (g/mL) 20.998 g 20.996 g 25.910 g 25.939 g 4.912 g 4.943 g .982 g/mL .987 g/mL 20.997 g 25.936 g 4.939 g .988 g/mL (6 pts) DQ2. Based on your entries in Table 1, what is the average density of deionized water resulting from your measurements with: (a) a beaker (b) a graduated cylinder and (c) a volumetric pipette? The average density of deionized water based on the entries in Table 1 for a beaker is .6 g/mL. This can be calculated by adding all of the individual densities in the beaker portion of the table and dividing it by three because there are only three densities recorded in the table and then rounding to one place after the decimal. Thus, the result is .6 g/mL because the calculation would be (.6246 g/mL + .5984 g/mL + .6366 g/mL)/3 which equates to .619866 which is rounded to .6 g/mL. With the same process the average density for a graduated cylinder is .90 g/mL because the calculation is (.9092 g/mL+ .8666 g/mL + .9122 g/mL)/3 which equates .896 but 2 significant figures after the decimal point is given so is rounded to .90 g/mL. Additionally, this process is repeated for the volumetric pipette but three significant figures are recorded after the decimal point. With that being said, the calculation for a volumetric pipette (.9824 +.9886 +.9878)/3 which is exactly .986267 but is rounded to .986 g/mL. (10 pts) Table 2: A sample table summarizing measurements leading to the density of a solution. Saline Solution P. Sotelo SP2022 4 30 mL beaker Trial 1 Trial 2 Trial 3 Graduated Cylinder Trial 1 Trial 2 Trial 3 Volumetric Pipette Trial 1 Trail 2 Trial 3 Empty beaker (g) Beaker + water (g) Mass of water (g) Density (g/mL) 20.999 g 25.212 g 4.213 g .8 g/mL 21.001 g 20.998 g 25.679 g 25.696 g 4.678 g 4.698 g .9 g/mL .9 g/mL Empty beaker (g) Beaker + water (g) 20.998 g 20.995 g 20.994 g 26.079 g 25.996 g 26.038 g Empty beaker (g) Beaker + water (g) Mass of water (g) 5.081 g 5.001 g 5.044 g Mass of water (g) Density (g/mL) 1.02 g/mL 1.00 g/mL 1.01 g/mL Density (g/mL) 20.973 g 26.525 g 5.552 g 1.110 g/mL 20.995 g 26.517 g 5.522 g 1.104 g/mL 20.995 g 26.539 g 5.544 g 1.109 g/mL (6 pts) DQ3. Based on your entries in Table 2, what is the average density of your saline solution resulting from your measurements with: (a) a beaker (b) a graduated cylinder and (c) a volumetric pipette? Based on the entries in Table 2, the average density of the saline solution for a beaker is calculated by adding all three individual densities for a beaker and then dividing by three because there are only three densities recorded and rounding to one significant figure behind the decimal point. Thus, the average density for a beaker with saline solution is .9 g/mL because the calculation is (.8426 g/mL + .9356 g/mL + .9396 g/mL)/3 resulting in .905933 which is rounded to .9 g/mL. With that same process the density of a graduated cylinder is found but is rounded to two significant figures behind the decimal point. The average density for a graduated cylinder is then 1.01 g/mL because the calculation is (1.0162 g/mL + 1.0002 g/mL + 1.0088 g/mL)/3 which is exactly 1.0084 but rounded to 1.01 g/mL . Additionally, the same process is repeated for a volumetric pipette but three significant figures are recorded behind the decimal place. The calculation is (1.1104 g/mL+ 1.1044 g/mL + 1.1088 g/mL)/ 3 which results in 1.10787, rounded to 1.108 g/mL. (6 pts) DQ4. When preparing the saline solution, you used 15-18 g of NaCl in about 80 mL P. Sotelo SP2022 5 of water. Calculate the predicted (theoretical) concentration of the saline solution in terms of % by mass using your exact mass of NaCl, the volume of water (80.0 mL), and density of water being 0.9981 g/mL. Show the calculation in detail with the corresponding units of measurement and the appropriate sig. figs. To calculate the theoretical concentration of the saline solution in terms of percent by mass you must first convert the volume of water into grams: (80 mL x 0.9981 g/mL) = 80.0 g. Additionally the next step is to divide the mass of NaCl by the total mass (15.484 g) NaCl/ (80.0 g water + 15.484 g NaCl) = 0.162163 x 100 = 16.2163% which is rounded to two significant figures: 16% by mass. (6 pts) DQ5. Use the following information to calculate the experimental value for the concentration (% by mass) of your saline solution based on your experimental value for density obtained with the volumetric pipette. You must show all the work and the calculation leading to the result in detail for full credit. *Density of deionized water at the working laboratory temperature was 0.9981 g/mL. To calculate the experimental value for the concentration (% by mass) of saline solution based on the experimental density obtained from the volumetric pipette use the equation of the line best fit for the relationship between density and saline solution. More specifically, take the average density for all three trials in the saline solution with the volumetric pipette and set it equal to the line best fit. - Y= 0.0076x + 0.9935 o Equation of line best fit for relationship between density and concentration of saline solution - 1.108 g/mL o Average density of saline solution using volumetric pipette o (1.1104 g/mL+ 1.1044 g/mL + 1.1088 g/mL)/ 3 which results in 1.10787, rounded to 1.108 g/mL.) 1.108 = 0.0076x + 0.9935 o .1145 = .0076x o X = 15.0658 = 15% - P. Sotelo SP2022 6 Table 3. Densities of saline solutions with respect to their concentration (% by mass). concentration density NaCl(aq) (g/mL) (% by mass) 5 10 15 20 25 30 1.032 1.070 1.105 1.144 1.186 1.220 Figure 1. A representation of the relationship between density and concentration of a saline solution (selected data). A linear trendline was the best fit; the corresponding mathematical expression is presented within the plot. (3 pts) DQ6. Calculate the % error between your theoretical and your experimental concentrations of your saline solution. To find the percent error between theoretical and experimental concentration of the saline solution the formula is (|experimental value – theoretical|)/theoretical x 100 - |(15 – 16)/16 | x 100 = 6.25 = 6.0% error (5 pts) DQ7. Discuss in detail various observed or reasonably predictable/suspected experimental errors. (The term “human error” should not be listed.) What would you do P. Sotelo SP2022 7 differently to prevent errors, improve outcome, etc. if this experiment was to be repeated? Perhaps some observed or reasonably suspected experimental errors was not cleaning the beaker properly, leading to inaccurate ‘empty beaker’ measurements. Additionally, other errors could be not filling to 5 mL exactly on all the glassware which could also lead to skewed results. Both these errors can contribute to false densities. To prevent these errors and improve the quality of the data, inspecting all glassware before going to measure the ‘empty beaker’ mass could improve results. Additionally, attempting to be better at measuring all liquids in the glassware so the data can be more reliable. (10 pts) POST-LAB NOTEBOOK PAGES (0.5 pts) Sample calculation 1: Calculate the mass of water obtained using a beaker for trial 1 (weight difference). (1 pts) Sample calculation 2: Calculate the density of water for a beaker in trial 1. (0.5 pts) Sample calculation 3: Calculate the mass of water obtained using a graduated cylinder for trial 1 (weight difference). (1 pts) Sample calculation 4: Calculate the density of water for grad. cylinder in trial 1. (0.5 pts) Sample calculation 5: Calculate the mass of water obtained using a volumetric pipette for trial 1 (weight difference). (1 pts) Sample calculation 6: Calculate the density of water for the volumetric pipette in trial 1. (0.5 pts) Sample calculation 7: Calculate the average density of water for measurements with all three types of glassware. (0.5 pts) Sample calculation 8: Calculate the mass of saline obtained using a beaker for trial 1 (weight difference). (1 pts) Sample calculation 9: Calculate the density of saline for a beaker in trial 1. (0.5 pts) Sample calculation 10: Calculate the mass of saline obtained using a graduated cylinder for trial 1 (weight difference). (1 pts) Sample calculation 11: Calculate the density of saline for grad. cylinder in trial 1. (0.5 pts) Sample calculation 12: Calculate the mass of saline obtained using a volumetric P. Sotelo SP2022 8 pipette for trial 1 (weight difference). (1 pts) Sample calculation 13: Calculate the density of saline for the volumetric pipette in trial 1. (0.5 pts) Sample calculation 14: Calculate the average density of saline for measurements with all three types of glassware. P. Sotelo SP2022 9 P. Sotelo SP2022 10