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Project 1: Calorimetry CHM 2046L-017 62406 9, February 2017

Introduction Background: Chemical reactions can consist of either the expulsion or consumption of energy, this energy comes in the form of heat in units of Joules. When a reaction releases heat, it is exothermic, and when it absorbs heat it is called exothermic. Calorimetry is the study of heat transferred in a chemical reaction, and an instrument called a calorimeter is used to measure this heat. One important application of calorimetry is when it is used as a nondestructive assay technique for determining to power output of nuclear materials. Calorimetric assay is a method for determining the mass of radioactive material through mass spectroscopy and calorimetry. It has been used by US and European facilities to process measurements of plutonium and test the accountability of nuclear materials for decades. (Bracken, Rudy) Heat capacity is the temperature change experienced in the reaction chamber as the reaction takes place in units of J/oC. The specific heat capacity is the amount of heat required to change the temperature of 1 g of a substance by 1 degree Celsius. The specific heat of the chamber and the temperature change recorded can be used to calculate the heat capacity of a calorimeter by the equation q=heat capacity* change in temperature (Chem 103 Laboratory Manual, Experiment 6 1) Theory: The main concepts that need to be understood in order to perform this experiment correctly are an understanding of how to prepare and dilute solutions, calibrate a calorimeter, stoichiometric calculations, calculate heat capacity and enthalpy, and using Excel to calculate the average and standard deviations Objectives: The objectives for this experiment are to determine the heat capacity of a coffee cup calorimeter and a commercial calorimeter, and use that information to calculate the enthalpy of acid base and redox reactions. From this data, one can come to the final conclusion of which calorimeter is most effective at preventing heat loss. Hypothesis: The coffee cup calorimeter will be a better insulator and cause less heat to escape during reaction than the commercial one, thus allowing it to have a higher heat capacity

Methods Materials - General lab glassware - Coffee cup and commercial calorimeters - Thermometer - 100 ml of DI water (50 hot and 50 cold) - Styrofoam cup - 3 M NaOH and HNO3 - Stir rod Part 1: The first step in this part of the experiment is to construct a coffee cup calorimeter. To do so, first retrieve a Styrofoam cup and a piece of cardboard. Cut a circle out of the cardboard and then poke two smaller holes in the circle, one for a thermometer and the other for a stir rod, this will serve as the lid for the calorimeter. Next, pour 50 ml of water into a 50 ml graduated cylinder, record the temperature using an alcohol thermometer, and pour it into the calorimeter. Heat another 50 ml of water to 63.5 degrees Celsius in a 150-ml beaker and pour it into the calorimeter. Once both samples of water are inside the calorimeter, seal it with the cardboard lid to minimize heat leaks. Stir the contents with the stir rod and take the temperature at 10 second intervals until it reaches equilibrium, which is when the temperature remains constant for several minutes or begins to drop. Record the temperature at equilibrium and use it in combination with the initial temperature of the cold water to determine the change in temperature that occurred during the reaction. Calculate the enthalpy of the reaction using q=m*C*∆T. Repeat the above steps for the commercial calorimeter, performing three trials for each calorimeter, and compare the enthalpies of both reactions. In this part of the experiment, it was decided that the water would be heated to 63.5 degrees Celsius because it was agreed that this would be the optimum temperature to produce an effective reaction. The temperature was recorded at 10 second intervals to ensure that an accurate measure of temperature change during reaction was obtained.

Part 2 Acid Base Reaction For the acid-base reaction, pour 50 ml of 3M NaOH and HNO3 using separate graduated cylinders and then transfer each chemical to its own 250 ml volumetric flask. Dilute the solutions to 1M in their respective flasks by adding 100 ml of DI water to each and inverting until they are thoroughly mixed. Measure out 25 ml of NaOH and HNO3 using separate graduated cylinders and transfer each to a 50 ml beaker. Pour the 1M NaOH into the coffee cup calorimeter and record the temperature with the alcohol thermometer, and do the same with the 1M HNO3. Once both contents are inside, quickly seal the lid to minimize heat leaks. Stir the solution using the stir rod and record the temperature until it remains constant or begins to drop. Once the solution reaches equilibrium record the temperature. Calculate the change in temperature and enthalpy of reaction as in the first part of the experiment. Repeat this process for a minimum of 1 trial with each calorimeter, but the goal is to complete 3 trials with each calorimeter. : During this portion of the experiment, NaOH and HNO3 were chosen as the components of the acid base reaction because they were readily available in the lab and since the reaction is in a 1:1 ratio then it would be easy to perform the necessary calculations. The same reasoning was used when deciding on the metal for the redox reaction as well. Redox Reaction The steps for the redox reaction are the same as above, but 250 mg of Mg should be substituted for NaOH. 250 mg of Mg was selected because adding to much to the solution would make the reaction take a lot longer. Safety - Wear PPE at all times - Only use small amounts of chemicals - Wash hands before and after experiment - Dispose of waste in the proper container - Use caution around the hot plate MSDS H2O- no known hazards, but its slippery nature can cause accidents HNO3- Corrosive. do not inhale, ingest, or put in contact with skin or eyes. Store in a well-ventilated area and wear PPE at all times NaOH- corrosive. Do not inhale, ingest, or put in contact with skin or eyes. Store in a well-ventilated area and wear PPE at all times Mg- do not inhale, ingest or put in contact with skin or eyes. Store in a well-ventilated area and wear PPE at all times Results Table 1: Part 1 Coffee Cup Calorimeter Trials Cold Water (Ti) Hot Water (Ti) 1 20.8 C 63.5 C

2

20.1 C

63.5 C

3

19.1 C

63.5 C

Final Temp 20s 38 C 40s 38.9 C 60s 38.9 C 80s 38.9 C 20s 38.8 C 40s 39.2 C 60s 39.2 C 80s 39.2 C

Mass in grams 100 g

20s 40s 60s 80s

100 g

38.5 C 38.8 C 38.8 C 38.8 C

100 g

Table 2: Part 1 Commercial Trials Cold Water 1 20.8 C

Hot Water 63. 5 C

2

20.2 C

63.5 C

3

20.5 C

63.5 C

Final Temp 20s 33 C 40s 34.9 C 60s 35.5 C 80s 35.5 C 20s 34.9 C 40s 37.6 C 60s 37.6 C 80s 37.6 C 20s 34.5 C 40s 37.0 C 60s 37.0 C 80s 37.0 C

Mass in grams 100 g

100 g

100 g

Table 3: Part 2 Acid Base Reaction (1HNO3 + 1NaOH -> H20 + NaNO3) Calorimeter Initial Temp Final Temp Coffee Cup

22.5 C

Commercial

22.2 C

Table 4: Part 2 Redox Reaction Calorimeter Initial Temp Coffee Cup 21.9 C

Commercial

22.5 C

10s 20s 30s 40s 50s 60s 70s 10s 20s 30s 40s 50s 60s 70s

25 C 26 C 26 C 27 C 26 C 25.5 C 25.5 C 24.1 C 24.9 C 25.0 C 24.9 C 24.9 C 24.6 C 24.6 C

Final Temp 10s 23.9 C 130s 35.4 C 250s 40.1 20s 26.2 C 140s 36.2 C 260s 40.1 30s 27.3 C 150s 37 C 270s 40.2 40s 28.1 C 160s 37.5 C 280s 40.2 50s 29 C 170s 38.1 C 290s 40.1 60s 30.1 C 180s 38.4 C 300s 40.1 70s 31.9 C 190s 38.9 C 310s 40.1 80s 31.9 C 200s 39.0 C 320s 40.1 90s 33 C 210s 39.0 C 100s 34.3 C 220s 39.1 C 110s 35 C 230s 39.2 C 120s 35.3 C 240s 39.8 C 10s 23 100s 29 190s 30 20s 25 110s 29 200s 30 30s 27 120s 28 210s 30

40s 27 50s 28 60s 29 70s 29 80s 29 90s 29

Table 5: Heat Capacity for Coffee Cup Part 1 Trial Change in Temperature 18.1 19.1 19.7

1 2 3 AVG

7559.40 7997.05 8227.64

Table 6: Heat Capacity for Commercial Part 1 Trial Change in Temp 14.7 17.4 16.5

1 2 3 AVG

Heat Capacity (J/g)

334 J/g

722.1 J/g

Calorimeter Constant 13.7 J/C 21.6 J/C 11.9 J/C 15.7 J/C

Heat Capacity (J/g)

Calorimeter Constant

6139.41 7267.05 6891.17

17.4 J/C 13.1 J/C 12.4 J/C 14.3 J/C

Table 7: Heat Capacity of Acid Base for Both Calorimeters Calorimeter Q Acid Q base Q calorimeter Styrofoam 334 J/g 837.4 J/g 1227 J Commercial

130s 28 220s 31 140s 28.5 230s 31 150s 29 160s 29 170s 29.5 180s 30

187.92

Q soln 1744.1 J

Q rxn -1234.2 J

1056.1 J

-1117.3

∆Hrxn -44.5 kj/mol -35.8 kj/mol

Table 8: Heat Capacity of Redox for both Calorimeters Calorimeter Styrofoam

Q Acid 334 J/g

Q metal 765 J/g

Q calorimeter 192.72 J

Q soln 1099 J

Q rxn -1291.7

Commercial

334 J/g

765 J/g

42.9 J

1099 J

-1114.7

∆Hrxn -10.84 kj/mol -10.53 kj/mol

Calculations - Balanced Equations o NaOH +HNO3 -> NaNO3 + H2O o Mg(s) + 2HNO3(aq) -> Mg(NO3)2 + H2 - Dilution Equation- used to dilute 3M NaOH and HNO3 to 1M o M1VI = M2V2 (initial concentration * initial volume = final concentration * final volume) o (3M)(x)= (1M)(150 ml) o x= (1M)(150 ml)/(3M) o x= 50 ml - Amount of HNO3 needed for complete reaction with 250 mg Mg o (250 mg Mg)* (1 mol Mg/24.31 g Mg) * (2 mol HNO3)/(1 mol Mg) = .0206 mol HNO3 o

Molarity=

moles solute liters solvent

.0206 mol HNO 3 L 1M. o L HNO3 = .0206 mol HNO 3 o

-

-

1 M= .

o Need at least 20.6 ml of HNO3 for reaction to go to completion Trial 1- Part 1 o Q=m*C*∆T heat= mass in grams*heat capacity*change in temperature (final-initial) o QHot= (100) (4.184) (18.1) = 7559.40 J/g o Qcold= (100 g) (4.184) (21) = 8786.4 J/g o Qcal= Qcold- Qhot= 8786.4-7559.40= 1227 J o Ccal= Qcal/∆T = (1227 J) / (19.1) = 64.24 J/C ∆Hrxn Styrofoam o Qacid= q*m*C*∆T= (50 g)(1.720)(4)= 334 J/g o Qbase= (50 g)(4.186 J/C)(4)= 837.4 J/g o Qcal= Ccal * ∆T = (64.24)(4 C)= 257 J o Qsolution = Qacid + Qbase = 1171.4 J o Qrxn= -(Qsolution + Qcal)= -1234.2 J o ∆Hrxn= Qrxn/number of moles= -1234.2 J/2.775 mol H2O= -44.5 kj/mol o percent error= (57.62-44.5)/ 57.62 *100= 23%

Discussion Part 1: In this part of the experiment, it was decided that the water would be heated to 63.5 degrees Celsius because it was agreed that this would be the optimum temperature to produce an effective reaction. Comparing the temperatures garnered in Table 1 and 2, the coffee cup calorimeter put out a higher rate of reaction than the commercial one, with the temperatures between 38-39 degrees Celsius for the coffee cup and 33-37 degrees for the commercial calorimeter. These results suggest that the initial hypothesis of the coffee cup calorimeter possessing a higher heat capacity is correct. It can be surmised that the coffee cup has a higher heat capacity because Styrofoam is more conductive than the glass chamber in the commercial calorimeter. This is further supported by the data in Tables 5 and 6, where the heat capacity of each calorimeter during each trial was calculated using q=m*C*∆T. The heat capacity for the coffee cup was between 7500-8200 J/g and the heat capacity for the commercial calorimeter was only in the range of 6000-7000 J/g. The average calorimeter constant was also higher in the coffee cup as per Table 5 which was 15.7 J/C compared with 14.3 J/C in Table 6 for the commercial calorimeter. Part 2: Only one trial was completed for each reaction in both the commercial and coffee cup calorimeters due to time restraint, so it is uncertain whether the results are reproducible. Based on the data given in Tables 3 and 4, the acid base reaction occurred much faster in both calorimeters, with 70 seconds passing before temperature remained constant, while the redox reactions took between 230-330 seconds to complete. The data also reiterates the previous finding from the first part that the coffee cup calorimeter is a better insulator than the commercial one for both reactions. This is noted again in Tables 2 and 3, where the initial temperature for both reactions ranged between 2340 degrees Celsius as opposed to the commercial one where temperatures fell between 23-31 degrees Celsius. The all of the data in table 7 and * illustrate that the coffee cup calorimeter possesses a higher heat capacity. For example, the heat of reaction was -1291.7 for the redox reaction in the coffee cup and -1114.7 in the commercial one Sources of Error Experimental error in the procedure occurred when the timer was not started at the appropriate time, but this did not have a large impact on the overall experiment. Conclusion Overall, the initial hypothesis that the coffee cup calorimeter would have a higher heat capacity was correct given the results of the experiment and the data presented. This is due to the fact that coffee cup calorimeter was made of Styrofoam, which is a stronger insulator than the glass reaction chamber in the commercial one. The results may have turned out differently if the commercial calorimeter contained a reaction chamber made of a more conductive

material, such as aluminum rather than glass. A suggested change to the experiment would be to find a better material to seal the coffee cup calorimeter because heat could escape quite easily, altering the experimental results. Research Connection The article "Solution calorimetry: a novel perspective into the dissolution process of food powders." describes an experiment whose objective was to study the heat evolved when maltodextrin and skim milk dissolve through isothermal solution calorimetry. This type of calorimetry is performed using a Tian Calvet Calorimeter, which has an aluminum chamber and a small opening for the stir rod. An image of the calorimeter was provided in the article and can be seen below. Researchers found that because the powders crystallized when added to solution that the reaction was less exothermic than expected. Thus, the state of the powder had a significant impact on the reaction results and a shapeless powder dissolved much faster than the recrystallized form. This research relates to the experiment performed in the lab in that it uses calorimetry to find the heat absorbed or released by a reaction, which was the goal of the in-class experiment.

References Marabi, A.; Mayor, G.; Raemy, A.; Bauwins, I.; Claude, J.; Burbidge, A. S.; Wallach, R.; Saguy, I. S. Food Research International 2007, 40(10), 1286–1298.

Chem 103 Laboratory Manual, Experiment 6. 1st ed. Web. 1 Feb. 2017. Bracken, D. S.; Rudy, C. R. Principles and Applications of Calorimetric Assay....