#7 Noteboom Asa Preeti Bhattacharjee, Lab Report

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Feb 20, 2024

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Asa Noteboom, Dylan Minnich Preeti Bhattacharjee 21059 3/12/2023 Determining the Heat Exchanged in Chemical Reactions Safety and Waste Disposal plan (short paragraph): In the lab in order to stay safe we wore goggles as always and this time when we weren’t using the computer we wore gloves in order to protect our hands from the reagents. We also used mixing cups and other devices in order to minimize possible contacts. Waste was all collected in a singular waste container that we acquired and then taken to a class disposal bin where it was later treated and properly disposed of. Materials and methods: We started the lab by setting up the cup and the thermometer correctly and starting logger pro on the computer. For part 1 we added a 100 mL of water, measured out 5.6-5.8 g of Mg(OH)2, started the magnetic mixer and started to mix the water and Mg(OH)2 to create a slurry. Record the initial temp and final temp of the solution, final temperature is determined to be when the line on logger pro stops increasing and flat lines, this is true for all parts. Part 2, restart Logger pro and mass out 7-9 g of citric acid. Add the massed acid into the mixture slowly so that the dust doesn’t fly everywhere and then observe the change in temperature, make sure to record the initial and final temp. Part 3, make sure to clean and empty out the cup of the previous two parts solutions and then add 100 mL of new water. Then mass out the same amount of citric, start logger pro and mix the acid with the water. Observe the change in temperature and record initial and final temp. Part 4 mass out same amount of Mg(OH)2 as part 1 and add it to solution and record the initial and final temp of solution. With all collected data now perform calculations of qrxn, ΔHrxn, and ΔHtotal. Data, Observations, Equations, and calculations: In the lab we used Mg(OH)2 which is a white chalky looking substance and when mixed in water it creates a white milk appearing liquid with the viscosity of water. When you add citric acid nothing changes to the solution visibly. Citric acid is white salt looking substance and when mixed in water it completely dissolves into the solution. When you add Mg(OH)2 to the citric acid (aq) it then turns into the white milky solution just as the first reaction did. Table 1: Recorded Mass of Chemical Reaction and Calculated Values Reaction # Mass base added (g) Mass acid added (g) Volume acid solution (mL) Volume water added (mL) Initial temp (°C) Final Temp( °C) Delta T (°C) qrxn (J) ΔHrxn (J/mol) ΔHtotal (J/mol) 1 5.707 100. 21.0 20.9 -.1 40.7 416.2 206902. 1 2 5.707 7.9787 100. 20.7 30.4 9.7 -3950.7 -208150.7

3 8.0577 100. 21.1 18.7 -2.4 925.7 24116.1 -208784 4 5.6812 100. 100. 18.7 30.8 12.1 -4927 -257016.2 Calculations Part 1: MgOH 2 (s) = Mg(OH) 2 (slurry) Part 2: 2H 3 C 6 H 5 O 7 (s) + 3Mg(OH) 2 (slurry) = Mg 3 (C 6 H 5 O 7 ) 2 (aq) + 6 H 2 O(l) Part 3: H 3 C 6 H 5 O 7 (s) = H 3 C 6 H 5 O 7 (aq) Part 4: 2H 3 C 6 H 5 O 7 (aq) + 3Mg(OH) 2 (s) = Mg 3 (C 6 H 5 O 7 ) 2 (aq) + 6 H 2 O(l) Part 1: q reaction =-q solution = -(3.853J/g°C)(-.1°C)(5.7070g+100g) q reaction =-q solution = 40.73 J ΔH = (40.73 J)/((5.7070 g)(1 mol Mg(OH) 2 )/(58.3197 g Mg(OH) 2 )) ΔH = 416.2 J/mol Part 2: q reaction =-q solution = -(3.853J/g°C)(9.7°C)(13.6857g + 100g) q reaction =-q solution = -3950.7 J Limiting Reagent: ((5.7070 g)(1 mol Mg(OH) 2 )/(58.3197 g Mg(OH) 2 )) = .09786/3 X 6 mol H2O = .1957 mol H 2 O ((7.9787 g)(1 mol Citric acid)/(210.14 g citric acid)) = .03796/2 X 6 mol H2O = .1139 mol H 2 O ΔH = (-3950.7 J)/((.03796 mol citric)(1 mol rxn)/(2 mol citric)) ΔH = -208150.7 J/mol Part 3:q reaction =-q solution = -(3.853J/g°C)(-2.4°C)(8.0577g + 100g) q reaction =-q solution = 924.72 J ΔH = (924.72 J)/((8.0577g)(l mol citric)/(210.14g)) ΔH = 24116.1 J/mol Part 4: q reaction =-q solution = -(3.853J/g°C)(12.1°C)(13.7389g + 100g) q reaction =-q solution = -4927.0 J Limiting Reagent ((8.0577g)(l mol citric)/(210.14g citric)) = .03834/2 X 6 mol H2O = .1150 mol H 2 O ((5.6812g)(1 mol Mg(OH) 2 )/(58.3197 g Mg(OH) 2 )) = .09741/3 X 6 mol H2O = .1948 mol H 2 O ΔH = (-4927.0 J)/((.03834 mol citric)(1 mol rxn)/(2 mol citric)) ΔH = -257016.2 Part 1/2 : Δrxn = 3ΔH1 + ΔH2 Δrxn = 3(406.2 J/mol) + (-208150.7 J/mol) Δrxn = -206932.1 J/mol Part 3/4 : Δrxn = 2ΔH3 + ΔH4 Δrxn = 2(24116.1 J/mol) + (-257016.2 J/mol) Δrxn = -208784. J/mol Evidence and Analysis: a) What is the enthalpy of the reaction? Include both individual and class results in your evidence to support the claims you have made. Our two final enthalpies that we found from our two reactions, (part ½ and part ¾) were -206932.1 J/mol and -208784 J/mol respectively. These numbers were fairly average compared to the wide range of

numbers calculated by the rest of the class. However, the conclusion that can be made is the delta H of both reactions were both negative (exothermic), and it would seem that the rest of the class came to that consensus as well. b) What law in chemistry did you apply when you combined the individual enthalpy values to find the overall enthalpy of the reaction? The First Law of Thermodynamics was used to find the overall enthalpy of the reaction. This law implies that the total enthalpy change associated with a chemical reaction is the same whether the reaction occurs in one step or many different steps. c) What is the underlying law behind this experiment? How does the heat of the reaction relate to the heat of the surroundings? Define and explain the system and surroundings in each part of this experiment. The underlying law behind this experiment is Hess’s Law, which states that the enthalpy change of an overall process is the sum of the enthalpy changes of its individual steps. This principle can be used to determine how the heat of the initial reaction can relate to the heat of its surroundings. In this case the final delta H value was negative, meaning that the reaction was exothermic and the reactions involving the MgOH2 and citric acid within the calorimeter produced heat to its surroundings, which explains why our delta T (change in temperature) increased for both reactions. d) There is no information in the literature regarding the value of the ∆ 𝐻 reaction (Part 3). However, the enthalpy value for the dissolution of citric acid has been reported to be 19,215 ± 150 J/mole. How does your value compare to this value? Our values were somewhat comparable to this as our calculated enthalpy value for the dissolution of citric acid was 24116.1. Our value does not fall within the +/- 150 range of 19215 with a difference of about 4901.1. e) What two assumptions could have led to an error in this experiment? For each assumption indicate whether it will introduce a determinate or an indeterminate error to your results. Also indicate how will the values of q and ∆ 𝐻 be impacted. The biggest possibility of determinate error that could have occurred during this procedure was during the calculations. There were many calculations that were conducted in this procedure including finding the enthalpy of each of the four parts of the experiment and then using those values to calculate the overall delta H or enthalpy change of the whole reaction. Other possible determinate errors that may have occurred could be possible measurement or procedure errors, an example of this might be pouring the MgOH2 into the Citric acid solution already in the cup too quickly and causing the solution to lose potential heat if too much condensation occurred. An example of a possible indeterminate error that may have occurred during this procedure could have been related to the software we used in conducting the experiment, if the temperature measurements of the computer were off, then we may not have gotten an exactly accurate measurement. Reading and Reflection: In this experiment the first main concept that this lab used was Hess’s law of thermodynamics. The concept was applied in this experiment because what we did is we split the reaction up into two parts and Hess’s law states that the ΔH is equal to the sum of each individual reaction in the whole reaction. So

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for example ΔHrxn=ΔH1+ΔH2. We used this exact concept by splitting the reaction into two pieces and then adding the ΔH of each reaction to determine the overall ΔH of mixing citric acid and Mg(OH) 2 . The second concept that this experiment enforced was the neutralization reaction between an acid and a base. Neutralization is when an acid and a base react with each other and form water and a salt. In this experiment we didn’t measure any pH levels of the reaction but what proves that the reaction occurred and that the neutralization process happened is the change in temperature showing how the base and the acid reacted and formed water and a salt. This enforces the fact that when acids and bases mix they always neutralize each other and this was confirmed by the change in energy, which was exothermic. A real world application of Hess’s law is when you're eating food and looking at your total calories ingested. Since calories are a direct translation to energy in food you can use Hess’s law to calculate how much total calories you’ve ingested throughout every meal and how much total energy your body has accumulated because Hess’s law holds true. So you can know how much spare energy your body has to spend doing everyday activities. This experiment adhered to the principles of green chemistry. For example it follows the 3rd principle of green chemistry very nicely. The third principle talks about less hazardous chemical synthesis and for example this reaction produces water and a salt which are two very non toxic chemicals in terms of green chemistry. This experiment could be made greener by using a regular paper cup instead of a styrofoam cup. This change would fall into accordance with the 7th rule of green chemistry: Use of Renewable Feedstocks. The use of paper cups would be very beneficial even though the results might vary slightly because paper cups are biodegradable and pose no threat when disposed of unlike styrofoam cups. The modification that would need to be made would be that instead of using two styrofoam cups you would replace that with two paper cups and then perform the experiment as before. Works Cited: - De Waele, E.; Honoré, P. M.; Malbrain, M. L. N. G. Does the Use of Indirect Calorimetry Change Outcome in the ICU? Yes It Does. Current Opinion in Clinical Nutrition and Metabolic Care 2018, 21 (2), 126–129. https://doi.org/10.1097/MCO.0000000000000452. Self and Lab partner evaluation for group report: You must include this in your reports. Asa - In this lab we each took turns performing each part of the lab which included mixing the ingredients and massing them out, In the report I performed the table and calculations and reading and reflection. No issues when performing the lab, all went very smoothly and each partner felt like they put in the same quality and level of work, very satisfied with the outcome. Dylan- In this lab we were able to complete the procedure together effectively and quickly. In the lab report I answered all of the evidence and analysis questions as well as finding the works cited source. I had no issues in completing this lab and I am satisfied with the overall quality of the work.