Lab 1 Report

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Kennesaw State University *

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Chemistry

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Feb 20, 2024

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Report Sheet For: Introduction to Analytical Measurements Name: X All answers must be typed in black ink. Increase the space between questions to insert your answers. The grading rubric is provided separately. Prelab Question: 1. Read the description on page 29 (9 th , 26) of the textbook on weighing by difference . Write your own description in 25-50 words (add reference for paraphrasing). Remember this should be in your notebook, and it will be in your report too. This means using a negative value on the balance to determine a substance’s mass. Typically used for hygroscopic (water/moisture absorbing) reagents, this method involves weighing a closed bottle of dry reagent. Then, a small amount is poured into the receiver. Cap and reweigh the bottle. The difference is the weight. With an electronic scale, take the mass with the initial capped bottle, pour reagent, and reweigh. The negative value is mass. 2. Read the description on pages 31-32 (9 th , 28-29) about weighing errors. Write your own description in 150 -300 words. For this question, you can type it and then print it and cut it out of the paper and tape it into your notebook, rather than writing all of it by hand in your notebook, only to type it for your report. Minimizing vibrations and leveling an analytical balance is a keyway to reduce error because of a sensitive part called the load receptor. Keeping samples close to the center of the weighing pan is necessary to reduce uneven weight distribution. Samples must be at room temperature to be weighed to prevent errors in weighing caused by convective air currents. It is also important to use tweezers or tissue to place an object on the pan, as prints and dust from your hands may leave residue. Weighing a magnetic object often requires the use of a spacer (like a beaker) to counter the forces of attraction between the metal object and the weighing pan. It may also be necessary to weigh a known--standard-- mass and check the tolerance of the balance using an established list. Linearity error refers to a deviation by the sensor output when an object is weighed after the balance has been calibrated. It should be a straight line from the calibration value to the weighed value, but a mass error can occur. This can be caused by changes in room temperature or shifting of the balance/its surface. Harris, D. C., & Lucy, C. A. (2020). Chapter 2 Tools of the Trade. In Quantitative Chemical Analysis (pp. 29 – 32). essay, Macmillan Learning.

3. Read the description on pages 32-34 (9 th , 29-31) about burets. Answer these questions: a. Define parallax. (up to 30 words) A parallax is the error when reading volumes that occurs when your eye is not at the same height as the liquid. b. Why is black tape on a white card needed? (up to 30 words) This is useful when trying to locate the precise location of the meniscus. c. Describe how to deliver a fraction of a drop. (up to 30 words) You open the stopcock until part of a drop is hanging from the buret tip, touch the inside of your glassware to the tip, & tilt the glassware so the liquid envelops the droplet. d. Describe how to rinse a buret with new solution. (up to 30 words) Use small portions of a new solution & run it through the buret fully and tilt the buret. Repeat 1-2 times. 4. Read the description on page 34-35 (9 th , 31-32) about Volumetric Flasks. a. Define TC. (up to 10 words) “To contain”— will contain liquids at given temperature with accuracy b. Define TD. (up to 10 words) “To deliver”— will deliver liquids at a given temperature with accuracy c. Define schlieren. (up to 20 words) Streaks resulting from refracted light when you mix substances in a flask to achieve homogeneity d. Why is swirling of the liquid important? (up to 30 words) Swirling helps to avoid a change in volume when adding liquids and to help mix the substances being added together e. When is the cap/lid/top added to the volumetric flask? (up to 10 words) Once the liquid is at the correct level, add the cap so you can invert the flask and mix the contents 5. Read the description on page 35-38 (9 th , 32-33) about Pipets and Syringes. Describe how to use a transfer pipet. Write your own description in 150 -300 words. For this question, you can type it and then print it and cut it out of the paper and tape it into your notebook, rather than writing all of it by hand in your notebook, only to type it for your report. This tool will deliver a single fixed volume of a substance. The final drop will not be released and should not be forced. The accuracy of this pipet is greater than that of the measuring pipet, which is like a buret in terms of calibration. The tolerances of a transfer pipet are given by a standard table. The larger this pipet is, the smaller the relative uncertainty is. For example, the relative uncertainty of a 25-mL pipet is .15%, whereas the relative uncertainty for a 1-mL pipet is .6%. Use a rubber bulb to suck liquid slightly above the calibration mark. If liquid gets into the bulb, the bulb and solution must both be replaced. Suck up 2 full volumes

of liquid and discard them to rinse the pipet. Take a third volume above the calibration mark and cover the end of the pipet with your index finger. Press the pipet to the bottom of the vessel being transferred into and remove the bulb from the opposite end of the pipet to drain the pipet. Wipe the pipe clean with a tissue. The pipet is drained via gravity and the liquid must run down the sound of the transfer vessel, which allows the liquid to flow out easily. Hold the pipet against the vessel wall a moment longer after draining (do NOT blow out final drop), making sure the tool is vertical at the end of the process. Rinse the pipet with distilled water or soak when finished. Harris, D. C., & Lucy, C. A. (2020). Chapter 2 Tools of the Trade. In Quantitative Chemical Analysis (pp. 29 – 32). essay, Macmillan Learning.

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Experimental and Results Table 1. The analytical balance. Object Mass to  0.0001 g. Mean Mass Standard deviation Weigh boat 3.2533 g 3.2463 g 0.01572 g 3.2573 g 3.2283 g Filter Paper .2454 g .2210 g 0.02918 g .2290 g .1887 g Weigh boat + Paper 3.7380 g 3.7273 g 0.02731 g 3.7477 g 3.6963 g Weigh boat + Breath 3.2565 g 3.2349 g 0.01882 g 3.2218 g 3.2265 g Table 2a. The 10-mL Volumetric Pipet. Temperature Mass H 2 O delivered Exp. Volume (from Density) Mean volume Standard Deviation 21.0 9.967 g 9.687 ml 9.994 ml .2353 ml 21.0 9.972 g 9.992 ml 21.0 9.941 g 9.961 ml 21.0 10.33 g 10.35 ml 21.0 9.963 g 9.982 ml Sample Calculation of Density based on Temperature for Trial 2: ????𝑖?? = −5.421?10 −6 (21.0) 2 + 1.233?10 −5 (21.0) + 1.00013 = .9980 𝑔 /?? Sample Calculation of Experimental Volume based on found Density for Trial 2: ? = ? 𝑣 → .9980 𝑔 ?? = 9.972 𝑔 𝑣 (??) → 𝑣 = 9.972 𝑔 . 9980 𝑔 ?? → 9 .992 ??

Table 2b. The 25-mL Volumetric Pipet Beaker Volumetric Flask Graduate Cylinder Erlenmeyer Flask At Above Above At Table 3. Calibration of a Buret Volume Delivered (mL) ( VD ) (Cumulative) Mass of H 2 O (g) And beaker Temperature of water: 21.0°C Mass of 50 mL beaker: 29.31 g Mass of H 2 O (g) (Cumulative) (mass found minus mass of beaker) Corrected Volume ( CV ) based on Density (see Part B) ( two decimal places) Difference from Corrected Volume and Volume Delivered ( CV minus VD ), i.e. Correction (mL) 0.00 29.31 g 0.000 g 0.00 ml 0.00 ml 5.00 34.22 g 4.912 g 4.92 ml -0.08 ml 10.15 39.31 g 9.998 g 10.02 ml -0.13 ml 15.00 43.79 g 14.48 g 14.51 ml -0.49 ml 20.00 50.21 g 20.90 g 20.94 ml +0.94 ml 25.00 55.21 g 25.90 g 25.95 ml +0.95 ml 35.32 65.60 g 36.29 g 36.36 ml +1.04 ml 40.00 70.29 g 40.98 g 41.06 ml +1.06 ml 45.02 75.35 g 46.04 g 46.13 ml +1.11 ml 50.00 79.93 g 50.62 g 50.72 ml +0.72 ml Add the Figure produced from the above data that is similar to Figure 2-23 as found on page 45 of the textbook. Give it a title at the bottom of the figure. Ensure that the axes are labeled correctly. In this case, the dots are connected using the scatter function with straight lines and markers. No trendline or equation of the line is added.

-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 0 10 20 30 40 50 Correction (ml) Indicated Volume (ml) Indicated Volume vs Correction

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Post Lab Questions 1. In your analysis of Table 1, if the mean mass of the weigh boat is added to the mean mass of the filter paper, does that equal the mean mass of the mass of the weigh boat and the filter paper? Use up to 30-50 words for your answer. No, the mean mass of the weigh boat (3.2463 g) plus the mean mass of the filter paper (.2210 g) does not equal the mean mass of the weight boat + the filter paper. The actual mean mass of both was 3.7273 g, and the calculated one in this scenario is 3.4673. 2. In your analysis of Table 1, did your breath add any mass to the weigh boat? In your answer that is 30-50 words, describe the precautions that should be taken when using the analytical balance. My breath did add mass to the weigh boat. When using the analytical balance, it is important to take precautions and avoid wind or currents from a vent, talking at or breathing on the sample, and closing the balance door(s) when weighing. 3. In your analysis of Table 2a, how close is the mean volume to the expected volume? Discuss the precision and accuracy found for the 10 mL pipet. Use 30- 50 words. The mean volume in 2a was 9.994 ml, and the expected volumes were all different, with my standard deviation at .2353 ml. This indicates that my precision using the 10 ml pipet was not very good, and my accuracy was impacted as a result. However, my expected volume for trial 2 was 9.992 ml, which is -0.02 ml from the mean, which indicates that my trial 2 measurement may have been the most accurate. 4. Describe your results for Table 2b in 30-50 words. When observing the meniscus in 4 different types of glassware for liquid delivered using a transfer pipet, the beaker and the Erlenmeyer flask had the meniscus at the line. The volumetric flask and the graduated cylinder both had the meniscus above the line. 5. Based on the figure produced from Table 3. What is the largest correction? What is the smallest correction? The largest correction in table 3 was +1.11 ml in the second to last delivery, with the VD at 45.02 ml and the CV at 46.13 ml. The smallest correction in table 3 was -0.08 ml in the second delivery, with the VD at 5.00 and the CV at 4.92 ml. 6. Write a concluding statement (30-50 words) for this experiment touching on what was learned and describing the tolerances found for the selected pieces of equipment in comparison to data in the tables found in the textbook. This lab taught me that my human ability to control the amount delivered from a pipet to glassware and interpret a meniscus can be better or worse at times, and that using analytical tools takes time and practice. I learned the importance of caution when weighing a sample to ensure no extraneous factors will impact my measurements. I found that the beaker and the Erlenmeyer flask were the most accurate, which is interesting, because they have higher percent errors than the volumetric flask (lowest percent error) and the graduated cylinder (second lowest percent error).