FormalLabReport_PaigeJonathan2

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Paige1 Gravimetric Determination of Sulfate By: October 18, 2023 Lab Partner: Instructor: CHE 120 –

Paige2 Purpose: During the duration of this two-week experiment, students will quantitatively determine sulfate in an unknown. Statistical treatment will then be used on the results obtained. The analytical technique gravimetric analysis will be used to determine the percent sulfate and the amount of sulfate present in the unknown. Digestion and principles of stoichiometry will be used to find the percentage of sulfate. The second part of the lab involves statistical analysis of the results obtained within each group and the entire lab section. Introduction: Finding the percent / amount of an element in a compound takes multiple scientific methods to achieve success. Quantitative analysis is “the determination of the amount or percentage of one or more constitutes of a sample.” 1 In other words, quantitative analysis is finding a specific amount or percentage of an element/ compound using basic stoichiometric reactions such as oxidation, neutralization, combustion, etc. An example of a method that can be used to quantitatively analyze an element / compound is volumetric analysis. Volumetric analysis is essentially measuring the volume a substance fills. 2 For example combining a gas and a medal which creates H 2 . Gravimetric analysis is another method of Quantitative analysis. This method involves a constitute converted into a substance that can be “separated from the sample and weighed.” 3 An experiment can be done to find Chloride in a sample. The process includes making the Chloride become insoluble while “being pure and easily filtered.” In the experiment, silver (Ag) can be combined to form Silver Chloride which is insoluble leading to the ability to find the percent chloride in a substance. 4 Gravimetric analysis can be done through a process

Paige3 called Digestion. Digestion is the “dissolution of small particles and reprecipitation on larger ones resulting in particle growth and better precipitate characteristics.” 5 In other words, heating the sample so the precipitate can further crystalize to be easily filtered and weighed. Error is also to be expected in such an experiment and for error we assign values of uncertainty. In lab, we as students were tasked with finding the percent Sulfate in a compound through the amount of precipitate formed in the reaction. We used processes such as quantitative measurements to transfer the unknown into a watch glass. We added deionized water and HCl to the beaker. From there the objective was to add Barium Chloride BaCl 2 to the mixture in order to obtain the ion SO 4 2- . After the mixture is complete, the precipitate is left to coagulate. This process is called digestion which is a method of gravimetric analysis. The experiment was not able to be completed due to an unexpected error in coagulating the precipitate. The following class Dr. Webb gave each group their separate mass of sulfate (0.468g) and we were able to do the Statistical treatment of Experimental Data. After we had all of the data from each group, we performed the Q test. The Q test is the “ratio of gap to range.” 6 The test proved none of our data to be invalid. Next, we were able to calculate the Standard deviation and the section average. Standard deviation includes taking all data and subtracting by the average of all data. The average with uncertainty ended up being 55.8% ±1.6. Procedure: To begin the experiment a watch glass was weighed to the nearest 0.001 g. An uncertainty value was assigned to the mass and then through the use of a spatula 0.8 g of an unknown was placed into the watch glass. The unknown was sprayed with deionized water into a 400-mL beaker. 200- mL of deionized water and 2-mL of concentrated HCl was then added to the beaker containing the sample. The mixture was stirred with a glass rod until a clear solution

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Paige4 was observed. The solution was then heated on a heating apparatus just below boiling point. 25- mL of 0.8 M BaCl 2 was then added slowly to the solution through the use of disposable plastic pipette. The formation of a precipitate was observed and stirred for an additional 30 seconds. Digestion was now the task, and the solution was left on the heating apparatus just below boiling point for about 30 minutes. While the precipitate was digesting, a disc of Whatman number 40 filter paper was labeled with initials. The disc was folded in half, then half again. Once completely folded, the filter paper was weighed and estimated with uncertainty. Through the use of a wash bottle the filter paper was sprayed with deionized water and placed in a funnel. The precipitate cooled and settled. To check the sulfate being fully precipitated a drop of BaCl 2 was added without stirring. Next the precipitate was transferred to the filter, and a wash bottle was used to rinse crystals from the beaker into the filter. While filtration was occurring, 50-mL of deionized water was heated. The precipitate was then washed by pouring the heated deionized water over the precipitate in the filter. Next the filter paper and the precipitate was placed in the 250-mL beaker covered with a watch glass and was put in the drawer until the following class. The following class involved statistical treatment of the experimental data. The instructor was to lead the section through calculations necessary to calculate the percent sulfate in the sample and the necessary propagation of error calculations that are to be assigned to the value. The data from the lab section was then used to demonstrate the application of statistical methods to a data set using methods such as the Q test, average and standard deviation calculations. Data & Results: A. Determination of Percent Sulfate Mass of Watch Glass & Sample - 40.938g ± 0.001g

Paige5 Mass of Watch Glass – 40.120g ± 0.002g Mass of Sample 0.818g ± 0.002g Propagation of Error Calculation - √ 0.001 2 + 0.002 2 = 0.002 ? Mass of the Filter Paper & Precipitate – 1.810g ± 0.002g Mass of the Filter Paper – 1.342g ± 0.002g Mass of BaSO 4 – 0.468g ± 0.003g Propagation of Error Calculation - √ 0.002 2 + 0.002 2 = 0.003 ? Mass of Sulfate in Sample – 0.468g ± 0.003g (1.810 - 1.342 = 0.468g) Percent Sulfate in sample & Uncertainty – 57.2% ± 0.4% Relative Error - 0.003 0.468 = 0.00641, 0.002 0.818 = 0.0024, √ 0.00641 2 + 0.00244 2 = 0.4 % All Percent Sulfate values from Lab Section – 55.4%, 57.2%, 58.8%, 54.8%, 54.8%, 54.4%, 55.2% Q-Test Determination- No Outliers Present 58.8 - 57.2= 1.6 1.6/4.4 = 0.363 54.8 - 54.4 = 0.4. 0.4/4.4= 0.091 Average % Sulfate - 55.4% + 57.2% + 58.8% + 54.8% + 54.8% + 54.4% + 55.2% / 7 = 55.8%

Paige6 Standard Deviation = 1.6 x x - Avg (x – Avg) 2 58.8% 3 9 57.2% 1.4 1.96 55.4% -0.4 0.16 55.2% 0.6 0.36 54.8% -1 1 54.8% -1 1 54.4% -1.4 1.96 √ 15.44 6 = 1.6 Lab Section Average Percent Sulfate with Uncertainty – 55.8% ± 1.6% Discussion: The objective of the experiment was to find the percent sulfate in the unknown. Principles of stoichiometry were used along with techniques such as digestion. The task was to take an unknown and quantitatively transfer it beaker. From there deionized water and hydrochloric acid (HCl) were added. The beaker was then placed on a heating apparatus and gently heated just below boiling. To find the percent sulfate a precipitate was required. Barium Chloride (BaCl 2 ) was slowly added to the mixture. Settling at the bottom is the precipitate,

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Paige7 Barium Sulfate (BaSO 4 ). Digestion was supposed to solidify crystals however this did not occur. The final step of the experiment was inconclusive causing all of the students in the section unable to complete the lab. The experiment could have been messed up due to multiple sources of possible error. Possible sources of error include failure to keep the mixture at the correct temperature during the duration of the digestion. Other groups along with mine were very cautious of vigorously boiling the mixture. As a total we may not have heated the mixture up to the correct temperature which could cause the failure of solidifying the precipitates. Another possible source of error could have been failure to gently pour the Barium Chloride (BaCl 2 ) in the mixture. The act of pouring the Barium Chloride rapidly could have caused the mixture to become inconclusive and add to the difficulty of completing the experiment. Due to the incompletion of the experiment, Dr. Webb presented each group with the mass of sulfate that would have been determined through our analysis. For my group we had 57.2% sulfate which could be found by dividing the mass of BaSO 4 by the mass of the sample (0.468g/ 0.818g = 57.2%). For the mass of BaSO 4 and the mass of the sample the propagation of error was calculated by taking the error found in the measured values such as mass of watch glass & sample, mass of watch glass, mass of paper & precipitate, and finally the filler paper. To find the propagation of error the error from the measured values were squared, added and the square root was taken. The next step was to find the uncertainty of the percent sulfate. This was different than finding the propagation of error because addition/ subtraction was used while for the uncertainty multiplication/ division is used. The Relative error was determined by dividing the propagation of mass of sulfate by the mass of the sulfate and then propagation of mass of sample by the mass of the sample. Then these values were recorded and put through the same process of squaring, adding and the square root of that value was the relative error (0.4%). The entire lab

Paige8 section shared their results and Statistical analysis was performed on these results. To find the Average percent of sulfate we had to utilize the Q- test to determine if any of the group's data is statistically invalid. This test is used to eliminate data and to be used in standard deviation. To perform the Q test, we had to do the Q calc which is the Spread divided by the range. The number obtained is then examined through the use of the confidence chart to determine if the value will be eliminated from the data. Our lab section had no invalid data therefore we could calculate the average. The average was 55.8%. Next objective was to find the standard deviation which is found by taking absolute value the data value found (x) and subtracting from the average then squaring the number. Finally, the sum was taken and divided by the total percentages found by one leaving 6 values. The square root was then taken and left our section with a standard deviation of 1.6. This means the lab section average percent with uncertainty is 55.8% ± 1.6. Conclusion: The following experiment included finding the percent sulfate in an unknown through methods and processes, known as quantitative analysis and gravimetric analysis. Other branches of chemistry were used, such as stoichiometric methods like digestion helped to form coagulated crystals to help weigh the precipitate. The percentage sulfate was found and then furthermore analyzed through the use of statistical analysis.

Paige9 References: 1. Encyclopædia Britannica, inc. (n.d.). Quantitative Chemical Analysis . Encyclopædia Britannica. https://www.britannica.com/science/quantitative-chemical-analysis 2. Encyclopædia Britannica, inc. (n.d.-b). Volumetric analysis . Encyclopædia Britannica. https://www.britannica.com/science/volumetric-analysis 3. Encyclopædia Britannica, inc. (n.d.-a). Gravimetric analysis . Encyclopædia Britannica. https://britannica.com/science/gravimetric-analysis 4. Wired chemist . Gravimetric Analysis. (n.d.). https://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials/gravimetric- analysis#:~:text=An%20example%20of%20a%20gravimetric,be%20pure%20and%20easily %20filtered . 5. Wikimedia Foundation. (2023, March 30). Gravimetric analysis . Wikipedia. https://en.wikipedia.org/wiki/Gravimetric_analysis#:~:text=Digestion%20of%20the %20precipitate%3A%20The,growth%20and%20better%20precipitate%20characteristics .

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Paige10 6. Libretexts. (2023, August 29). The Q-test . Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analyti cal_Chemistry)/Data_Analysis/Data_Analysis_II/05_Outliers/01_The_Q-Test

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