Dolores RamirezExperiment #11-Thermochemistry II: Reaction Enthalpy and Hess’s LawDolores RamirezChem 2 Lab 2LoganMay 5, 2013Experiment #11-Thermochemistry II: Reaction Enthalpyand Hess’s Law1. Introduction: The purpose of this lab is to investigate the quantity of energy transferred by heat for chemical reactions. We also have to quantitatively determine the enthalpy change for several chemical reactions and to evaluate the validity of Hess’s law of constant heat summation.2. Experimental:a) Materials:Chemicals: 1.0 M hydrochloric acid; 1.0 M sodium hydroxide; solid sodium hydroxide.b) Apparatus:Two thermometers with 0.1°C divisions; two calorimeters assemblies (labeled A & B) with lids; heating assembly (hotplate); plastic pipets.c) Procedure: 1. Obtain four Styrofoam cups and two thermometers2. Each 2 –cup calorimeter is slightly different and the calibrations of the thermometers may also be slightly different, it is important to use the esame calorimeter and thermometer pair though the experiment3. Labe l one calorimeter “A” and the other “B”4. When using the calorimeters place them inside 250 mL to keep them in place.Part A: Determining the Calorimeter Constant.5. Compare the calibration of the two thermometers by immersing both thermometers in the same beaker of tap water for 1 minute and recording the reading of each (if different apply necessary corrections).6. Put 75mL of distilled water in a 125 mL Erlenmeyer flask and heat it on a hot plate 15-20°C above room temperature. 7. Using 50 mL graduated cylinder, transfer 50.0 ml of the heated distilled water into calorimeter A and 50.0 mL of room temperature distilled water in calorimeter B. 8. Place the lids on both the calorimeters and begin recording the temperatures of both calorimeters at 1 minute intervals. The warm water may cool slightly during this time because thermal insulation is imperfect.19. After 4 minutes, quickly remove the lids from both calorimeters, pour the cold water from calorimeter B into calorimeter A, replace the lid and continue taking temperature readings for the next three minutes. When your measurements are complete you may pour the water in the calorimeters down the drain.Part B: Enthalpy of neutralization of Aqueous HCL and NaOH10. Using a graduated cylinder to measure 50.0 mL of 1.9 M hydrochloric acid into calorimeter A, and 50.0 mL 0f 1.0 M sodium hydroxide into calorimeter B. 11. With the lids and thermometers in place, read the temperature of each solution at 1-minute intervals for 3 minutes. Then quickly pour the sodium hydroxide solution into calorimeter A, stir thoroughly, and continue reading the temperature for another 5 minutes at 1-minutes intervals. 12. Pour the solution in the calorimeter into a large beaker to combine with other parts and neutralize. 13. Rinse any pipets you used with water and toss in the “used Plastic Pipets” container.Part C: Enthalpy of solution of solid NaOH.14. Using a graduated cylinder measure 50.0 mL of distilled water into calorimeter A. 15. Weight about 2.0 g of sodium hydroxide pellets into a small bottle withcap. Weight the empty bottle and cap, then weigh the capped bottle with the sodium hydroxide and take the difference.16. Minimize the length of time the sodium hydroxide is exposed to the air. This is because sodium hydroxide is very hygroscopic (absorbs air).17. Measure the temperature of the water in the calorimeter at 1-minute intervals. After the 3 minutes, add the sodium hydroxide to the water in the calorimeter. 18. Stir constantly while recording the temperature at 1-minutes intervals. It will take a while (5minutes more) for all the sodium hydroxide to dissolve. Continue monitoring and recording the temperature for at least 4 minutes after all the solid has dissolved. 19. When you have recorded your data, pour the solution into the large beaker for neutralization.Part D: Enthalpy of Neutralization of Solid NaOH.20. Using a graduated cylinder to measure 50.0 mL of 1 M hydrochloric acid into calorimeter A. 21. Weigh accurately approximately 2.0 g of sodium hydroxide pellets intoa small bottle with a cap, as you did in Part C to minimize exposure to the room air.22. Measure the temperature of the 1 M hydrochloric acid in the calorimeter at 1-minute intervals. After 3 minutes, add the sodium hydroxide to the 1 M hydrochloric acid in the calorimeter. Stir constantly while recording the temperature at 1-minute intervals. 223. It will take a while (5minutes or more) for all the sodium hydroxide to dissolve. Continue monitoring and recording the temperature for at least 4 minutes after all the solid has dissolved. 24. Pour the solution into the large beaker for neutralizationClean Up.25. Neutralize all solutions to a pH between 6 and 8.3. Results and Discussion:All results to this experiment are found on page 4-9. Here I recorded the temperature for 1.0 M hydrochloric acid; 1.0 M sodium hydroxide; solid sodium hydroxide and water. In order to calculate the Ccal of my water I used equation: m coldH 20 ∙CH 20 ∙ ∆ TcoldH 20=−(mHotH 2 ∙CH 20 ∙ ∆THotH 20)−(Ccal ∙ ∆ THotH 20)In this equation I just plugged in the difference in temperatures of water and solved. I used water in my other equations to get the molar enthalpy for each of the solution in every part of the experiment. In order to get ∆ Trxn for each of the solutions before I solved for molar enthalpy I used:∆ Trxn=Tmxture−12(NaOH +THCl)4. Conclusion:As conclusion this experiment was successful. We were able to successfully find the quantity of energy transferred by heat for chemical reactions. We also have to quantitatively determine the enthalpy change for several chemical reactions and to evaluate the validity of Hess’s law of constant heat summation.a) Initialed Duplicate Laboratory Notebook Page(s):i. The initialed duplicate laboratory notebook page(s) must be included after your conclusion upon report submission.35. Report Questions:1)m cold H 20∙ CH 20 ∙ ∆ TcoldH 20=−(mHotH 2∙ CH 20 ∙ ∆ THotH 20)−(Ccal ∙ ∆ THotH 20)Ccal=−(mH 20∙ CH 20 ∙ ∆ THotH 20)−(mcoldH 20 ∙ CH 20 ∙ ∆ TcoldH 20)−∆ THotH 20∆ THotH 20=31.4−39.9=−8.5∆ TcoldH 20=31.4−21 .9=9.5Ccal=−(50 g ∙ 4.184Jg° C ∙−8.5° C)−(50 g ∙ 4.184Jg° C ∙ 9.5 °C )−8.5 ° CCcal=22.15Jg° C2)4∆ Trxn=Tmxture−12(NaOH +THCl)Temperature mixing time: 4 minutes; x=4Tmixture=−0.05(4)+25.02=24.82° CTNaOH= 21.9 °CTHCl=22.5