Stoichiometry: Determination of the Identity of a Metal Carbonate

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Feb 20, 2024

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2/27/2023 Stoichiometry: Determination of the Identity of a Metal Carbonate Safety and Waste Disposal plan (short paragraph): We were able to stay safe in this lab first of all because all of the chemical mixtures we were working with were not very hazardous substances so we weren’t needing to be extremely cautious but we still did use the proper equipment in order to avoid as much contact as possible with the experiment to prevent any injuries. We used pipettes and stirring rods and tweezers to not touch any solutions. The waste for this was very simple, we put the dried carbonate into a class disposal bucket and the excess solution was washed into a class disposal bin as well. Materials and methods: First we massed out between 1 and 2 grams of the unknown carbonate and recorded it. Then measured out 100 mL of water in the 400 mL beaker. Poured the unknown carbonate into the mixture and stirred it around a bit. Calculated the proper amount of SrCl2 needed to properly react with all of the unknown carbonate (used the smallest mass of carbonate). Added calculated amount to mixture and stirred, record observations about precipitation. Let it settle for a couple minutes then tested if all precipitation had occurred by taking a small sample of clear liquid from mixture and adding a drop of SrCl2, if no reaction occurs then proceed as instructed, if reaction occurs add more SrCl2 and perform test again, repeat until no more reaction occurs. Put all tested liquid back into the mixture. Then placed filter paper in the funnel and sealed it down with water. Slowly pour solution into the center of the filter paper after turning the vacuum on. Once all dried out by vacuum, turn the vacuum off and remove the filter paper put it on a tray and put it in the oven to dry for 25 minutes. Once removed, mass the sample and perform calculations necessary to find the unknown carbonate. Data, Observations, Equations, calculations, and graph: Started off as a white chalky powder. When mixed in the water initially turned the water a murky white. When Strontium solution was added a white cloud enveloped the mixture. Cloud settled down to the bottom leaving a clear layer at the top. After filtration the once cloud now looks like a thick white mud. Collected/Calculated Data of Unknown Carbonate Mass of Unknown (g) Mass of dry SrCO3 product (g) Mass of Carbonate in product (g) Mass of carbonate in unknown (g) % mass of carbonate from unknown Class average mass % carbonate in unknown S.D. Count 2.0788 2.030 .8252 .8252 39.70 40.69 2. Calculations should include: a) volume of strontium chloride used Volume = 2. 078 ࠵? ࠵?࠵?࠵?࠵?࠵?࠵?࠵? (1 ࠵?࠵?࠵? ࠵?࠵?/106 ࠵? ࠵?࠵?) (1࠵?/1࠵?) ࠵? 1000 Volume = 19.61 mL b) the percent mass of carbonate in your precipitate, in the original unknown, and in the three different carbonates under investigation % mass CO3 in Na2CO3 = (59.98 g CO3/105.96 g Na2CO3) x 100

% mass CO3 in Na2CO3 = 56.61 % % mass CO3 in K2CO3 = (59.98 g CO3/138.18 g K2CO3) x 100 % mass CO3 in K2CO3 = 43.41 % % mass CO3 in Rb2CO3 = (59.98 g CO3/230.92 g Rb2CO3) x 100 % mass CO3 in Rb2CO = 25.97 % % mass CO3 in SrCO3 = (59.98 g CO3/147.6 g SrCO3) x 100 % mass CO3 in SrCO3 = 40.64 % % mass of CO3 in X measured mass SrCO3 = (.4064)(2.03 g SrCO3) % mass of CO3 in X measured mass SrCO3 = (.8250 g CO3)/(2.0788 g unknown) x100 % mass of CO3 in X measured mass SrCO3 = 39.69% c) Include a balanced molecular chemical equation showing the reaction of your unknown with strontium chloride X2CO3(aq) + SrCl2 (aq) = SrCO3(s) + 2XCl(aq) d) Include graph for mass of carbonate in precipitate versus initial mass of the unknown e) Obtain the identity of the unknown from your TA. Calculate the percent error for the mass fraction of carbonate in your unknown compared to the actual value The actual identity of the carbonate is potassium carbonate so, % error = (|43.41-39.69|/43.41)x100 % error = 8.569 Evidence and Analysis: Please answer the following section by providing experimental evidence for each point. a) Report the identity of the unknown carbonate, based on your data. Report the identity of the unknown carbonate based on class data.

We found the unknown carbonate to be potassium carbonate (K2CO3). This conclusion was based on the mass percentage calculated in our findings (39.69%) which most closely resembled our percent mass calculation of K2CO3 (43.41%). b) All students in your section had the same unknown. Were their results consistent with your results in terms of mass percentage of carbonate in the unknown? If not, can you propose reasons why? Did it matter how much unknown compound was investigated with respect to percent of carbonate in the sample? Overall, our classmates all seemed to be in the same range as us with most groups mass percentage calculation to be around 40%. The reason for any subtle outliers may have been due to minor errors such as not getting an exactly accurate weight measurement on the scale or maybe there were some errors that could have occurred during the precipitation process. For instance, the filter paper may have not been completely sealed on top of the vacuum or perhaps the solution was poured onto the filter paper too quickly and did not allow for the reaction to properly take place.In this experiment it did not matter how much unknown compound was investigated with respect to the percent of carbonate in the sample. This can be supported by the fact that each group during the experiment was assigned to a different initial mass range, and we all concluded with comparable results. This is because this experiment was simply to find the mass percentage of the unknown carbonate rather than the total mass of the reaction. c) Report the actual identity of the unknown and the percent error for the mass fraction of carbonate in your unknown. Use determinate and indeterminate error considerations to explain why the value you calculated is different from the actual value. When considering sources of error, discuss any assumptions that may have been made. Our error percentage of our final calculated mass percentage of our sample versus the calculated mass percentage of K2CO3 was 8.569%. This is not far off, however this subtle inequality could be due to a few factors. One of which being an indeterminate error was that our vacuum was the one used in the demonstration of the procedure. Meaning that there could have been some excess solution involved in our final precipitate gathered on our filter paper. An example of a determinate error that could have taken place during our procedure was when gathering the supernatant and transferring it to the test tube. We may have not let the supernatant settle and form on the top of the solution long enough before reacting with the SrCO3. Reading and Reflection: use these questions to draft your reading and reflection section coherently in no more than 2 paragraphs. Use paragraph format, please avoid using bullet points for this section. a) What concepts were explored/applied in this lab. How does a concept or technique from this experiment connect to a real-world application? Explain briefly. Many techniques and concepts were used during this procedure. One fundamental concept was the use of stoichiometry to calculate our mass percentages of each of the possible listed carbonates as well as our own unknown carbonate. Stoichiometry is a technique used heavily in the making of specific medicines. Another daily application of stoichiometry is cooking and making recipes, as stoichiometry is the relationship between reactants and products before and after the reaction. Another real life application from this experiment is predicting certain reactions, in this case a precipitation reaction. Doctor’s and

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biologists have to predict specific chemical reactions within the body when prescribing medicine or recommending certain dietary restrictions or nutritional supplements to patients. b) Confirm, dispute, or explain your findings using appropriate literature values or sources. Include appropriate citations for these sources. The procedure we conducted and the results we found during our experiment can be compared to a similar experiment regarding a precipitation reaction involving finding a suitable method for minimizing the amount of precipitate being collected in underground water pipes. In the experiment they have to determine what the unknown precipitate is that is forming on the walls of the water pipes in efforts to mitigate this through liquid aquifers. (Cohen, p.2) The article focuses more on the aspect of the infusion of calcareous aquifers and they could be to inject a fluid that dissolves the existing carbonate minerals and induces the formation of phases that have higher molar volumes . (Grayevsky, p.2) Our experiments were however similar in the fact that we both dealt with an unknown carbonate and had to determine what it was to come to a conclusion. While the first article cited may not have dealt directly with K2CO3, the second article directly involves a reaction involving the use of K2CO3 in atmospheric CO2 removal. It was listed that they were able to find the mass percentage of their K2SO3 sample to be 42. 312% (Isa, p.3) which closely resembles our results as well as the rest of the class's data. Works Cited: You will need to cite relevant scientific research for this report that includes an article or two from the literature. The citation should be in ACS format. - Cohen, A.; Grayevsky, R.; Israeli, Y.; Emmanuel, S. Coupled Dissolution-Precipitation Reactions as a Potential Method for Mitigating Contaminant Transport in Carbonate Aquifers. Advances in Water Resources 2021, 157 , 104052. https://doi.org/10.1016/j.advwatres.2021.104052 . - Isa, F.; Zabiri, H.; Ng, N. K. S.; Shariff, A. M. CO2 Removal via Promoted Potassium Carbonate: A Review on Modeling and Simulation Techniques. International Journal of Greenhouse Gas Control 2018, 76 , 236–265. https://doi.org/10.1016/j.ijggc.2018.07.004. Self and Lab partner evaluation for group report: In this lab my partner and I worked together on this experiment and lab report, we each rotated doing the experiment. Meaning I started with massing out the unknown carbonate then he mixed them together and so forth. In the lab report I did the method and safety, evidence, and the table and calculations, this was because I just decided to do it sooner not because my lab partner wasn’t doing his portion. He did go over as well and make corrections to my work as he saw fit meaning he overviewed the whole report as well. Overall no issues working together and satisfied with the quality of work - During this lab procedure my lab partner and I were able to work together cohesively during the experiment as well as the lab report. We each were able to balance our duties during the actual experiment so that we moved through it more efficiently. For the lab report I answered all of the evidence and analysis questions as well as finding the citations and comparing our data and experiment to those mentioned in the articles. We were also able to check each other’s work and I feel satisfied with how the experiment went as well as the quality of work from both of us.