FormalLabReport_PaigeJonathan2

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Southern Connecticut State University *

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Chemistry

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Jan 9, 2024

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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
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
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