CHEM 152 Lab 3 Report
CHEM 152 Lab 3 Report CHEM 152
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This 10 page Class Notes was uploaded by Angel Lee on Tuesday June 9, 2015. The Class Notes belongs to CHEM 152 at University of Washington taught by Kevin O'Malley in Spring 2015. Since its upload, it has received 1192 views. For similar materials see General Chemistry in Chemistry at University of Washington.
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Date Created: 06/09/15
Name Quiz Section ID Lab Partner Chem 152 Experiment 3 Calorimetry By signing below you certify that you have not falsified data that you have not plagiarized any part of this lab report and that all Note calculations and responses other than the reporting of raw data are your own independent work Failure to sign this declaration will All sections of result in 5 points being deducted from your report score this report must be typed Signature Total Points 60 pts 5 notebook 55 template PURPOSE AND METHOD Our goals are to i Determine the heat capacity of the calorimeter ii Measure the enthalpy of fusion of ice iii Measure the enthalpy of neautralization iv Determine the enthalpy of hydration magnesium sulfate Explain how each of these is accomplished in this experiment Where appropriate include equations you will use to process your data 2 pts each 8 pts For the first part of the experiment a calorimeter water timer and a digital power supply will be provided To determine the heat capacity of the calorimeter we will record the time it takes for a known amount of heat to change the temperautre of the calorimeter filled with water to 32 degrees Celsius The following equation will be used to calculate the heat capacity of the calorimeter C cal q cal Cs JC s Tf Ti Tf Ti The average of the three trials will be used to determine the heat capacity of the calorimeter Once the heat capacity of the calorimeter is determined it can be used to measure the enthalpy of melting an ice cube Knowing that the heat lost by the calorimeter must be equal the heat gained by the ice water we will record the change in temperature and the mass of ice to solve for the enthalpy of fusion of ice The following equation can be used to determine the enthalpy C cal AT m iceAH fusion m ice4184 JgOC AT water from ice where AT water from ice Tf Ti In the third part of this experiment 05 M HCI 05 M NaOH and 05 M HCH3COO will be provided in the lab The first neutralization reaction will involve HCI and NaOH and the second will include HCH3COO and NaOH both of which are exothermic reactions Knowing that the heat gained by the calorimeter is equal to the heat lost by the exothermic reactions we can again use q CcaAT to calculate the enthalpy of the neutralization reactions In the final part of the experiment the enthalpy of hydration of MgSO4 will be determined by measuring the enthalpies of two related reactions The enthalpies of these reactions will be used with Hess s Law to calculated the enthalpy of hydration of MgSO4 Data Entry 6 pts DATA AND CALCULATIONS A Heat Capacity of the Calorimeter Run 1 Run 2 Run 3 Voltage v JC 3o 3o 3o Current A Cs 25o 250 250 Time s 211 206 204 Initial temperature C 280 280 280 Final temperature C 320 320 320 Energy into calorimeter from power supply q JI 158339 I 1545 I 1530 Heat Capacity of Calorimeter cw J C 396 386 383 Type an example of the calculations you are performing for q and Goal 3 pts Average Ccall 388 q cal voltage current time q cal 30 V 25 amps 211 sec 1583 J Standard Devl 7 Help with Formulas in Excel C cal g cal Tf Ti In Excel type quotaveragerange of valuesquot but instead of entering a range just click at one end C cal 396 JOC of the values and drag mouse to the other end For standard deviation in Excel type quotstdevrange of valuesquot B Enthalpy of Fusion of Ice Run 1 Run 2 A e Joc Type examples of the calculations you perform for the following Cca39 verag 388 388 a q cal 2 pts Mass of calorimeter stir bar and water 9 112805 112845 q cal C cal AT cal Mass of calorimeter stir bar and water OI 0339 388 J C 48 C 1863 J mass of added ice or melted ice 9 116860 116484 b q for heating the water that was Ice warming melted Ice 2 pts Mass Of Ice 9 439055 339639 q m ice 4184 Jg C AT water from ice Temperature of calorimeter before ice addition C 280 280 0 4055 g 4184 JgOC 228 0c 387J Temperature of ice before addition to AH It th I 3 t the calorimeter 0C C fusion me mg 9 Ice p 8 Temp of the calorimeter after addition AHfusion heat lost by calorimeter heat to warm water that was ice and melting of the ice C 232 239 mass 0f 39Ce ATcat 48 41 AHfusion 1870J 387J 366 Jg 4055g Heat lost by calorimeter q cal In J 15863 1591 ATwater from ice 228 239 Specific heat of water Jg C 4184 4184 Heat gained by ice cube to warm water from ice temperature q in J 387 364 Enthalpy of fusion of ice AH fusion in Jg 364 337 Average AH 351 Jg Standard Dev 19 Jg C Enthalpy of Neutralization of HCI and NaOH NaOH Concentration 050 M Volume Used 40 mL HCI Concentration 050 M Volume Used 40 mL Run 1 Run 2 Type examples of the calculations you are performing for CcaAverage J C 388 388 a moles of H20 produced by HCINaOH reaction 2 pts T HCI C 280 274 quotquotquotaquot o NaOH HCI gt H20 NaCl Tinitial NaOH C 2775 258 050M 0040 L 050 M0040 L Tini a average C 279 271 002 mol 002 mol T nal C 30394 30 neither is limiting so 0020 mol of H20 is produced AT C 25 29 Moles H20 formed in reaction 0020 0020 b the magnitude of the heat gainedlost 2 pts q J magnitude of heat gainedlost 980 15126 q cal C cal AT AH neutralization kJmOI 3949 3956 O 0 Average AH neutralization kJmo39 3953 q cal 388 J C 25 C 980J Standard Dev 5 C AIneutralization pts D and AHneutralization maqnitude Of the heat qained IOSt 39980 J 1 kJ 1000J moles of H20 formed in reaction 0020 mol NaOH Concentration 050 M Volume Used 40 mL 49 kJ mol Acetic acid Concentration 050 M Volume Used 40 mL Run 1 Run 2 CcaAverage J C 388 388 Tinitia acetic acid C 277 271 Tinitia NaOH C 274 267 Tini a average C 2755 269 T na C 304 30 AT C 29 31 Moles H20 formed in reaction 0020 0020 q J magnitude of heat gainedlost 1 5106 1 203 AH neutralization kJmOI 39553 39602 Average AH neutralization kJmo39 3958 Standard Dev 3 E Enthalpy of Hydration of Magnesium Sulfate Run 1 Run 2 I I I Ccalmverage Joc 388 388 Type examples of the calculations you are performing for performing for Mass added 9 a moes of soid a Moles of MgSO4 003879 003765 T C 27 8 27 4 moles of MgSO4 mass of M0804 4669 0 initiaquot 39 39 molar mass MgSO4 120366 gmol Tfinal C 356 353 AT C 73 79 mole of MgSO4 003879 mol q magnitude Of heat gainedIOSt 3 027 3066 the magnitude of q C AH solution kJmOI 78 81 Average AH solution kJmol 80 q cal 39 C cal AT Standard Dequot 2 q cal 388 JOC 78 C 30271 Run 1 Run 2 C AH solution 2 pts C a39Average Mac 388 388 AH 39t 0 fth h t 39 d I t 3 0271 1 k1 10001 neutralization magnl u e o e ea game 05 mass M9804 7 H20 added 9 1039176 1039196 moles of MgSO4 formed in reaction 003879 mol Moles MgSO47H20 004129 004137 78 kJ mol Tinitiala C 276 273 Tfinal 5 C 257 25 0 overall AH 2 pts AT 0C 391399 391396 Athdration AHdissqution of MgSO4 AHdissqution of MgSO4 7H20 q J magnitude of heat gainedlost 737 621 AH solution 16 96 Average AH solution kJmol 16 Standard Dev 2 d Enthalpy of Hydration kJmol Type the calculations you are performing for Ccup Cwater and RESULTS AND DISCUSSION the new Ccal 3 pts Cwater specific heat of water mass of water 1 If Ccal Ccup Cwater calculate Ccup and Cwater for this experiment Cwater 4184 JgOC 800 g 335 JOC Hint Use heat capacity of water Cwater 335 J C Ccup 53 Joc Ccup Ccal Cwater 2 What would Ccal have been if you had used 262 J C CcuI0 388 JOC 335 JOC 53 JOC 50 mL or 50 g of water instead 3 The literature value for the enthalpy of fusion of water is 334 Jg Calculate the o error for your result 2 pts Percent error lactual theorectical 100 351 J01 334 J01 100 17 J01 100 51 o theoretical 334 Jg 334 Jg The percent error for the value for the enthalpy of fusion of water was 51 percent A possible source of error could have been the fact that we carried out the experiment slightly differently for each trial For the first experiment instead of measuring the temperature of the calorimeter first we measured the temperature of the ice bath and then immediately right after the temperature of the calorimeter I particularly think this is what affected our results because I noticed the tip of digital thermometer was very cold when we immersed it into the calorimeter which could have resulted in the reading to be lower than it ought 4 How would a different mass of ice affect the determination of the enthalpy of fusion Explain 2 pts Theoretically changing the mass of ice in the experiment should not affect the determination of the enthalpy of fusion This is because with an increase in the mass of ice there is a corresponding increase in the magnitude of the temperature change of the calorimeter On the other hand because this is the real world a greater mass of ice should have yielded an enthalpy of fusion closer to that of the theoretical value This is because in this case the ice is like a sample and the more sample you have the more likely you are to get a closer value to the theoretical value 5 According to the Zumdahl textbook the enthalpy of neutralization for a strong acid and strong base is 58 kJmole see section 94 in Zumdahl Explain how I A JI LI IEJJ I IIJ LL n I J LL n In J your value compares With this literature value calculate the uo error and comment on the comparison Z pIS Percent error o l53 kJmol 58 kJmoll 100 5 kJmol 100 86 o 58 kJ mol 58 kJ mol My results yielded a percent error of 86 percent which is considered unacceptable according to the 5 percent rule The actual magnitude of the enthalpy of neutralization was higher than the magnitude of the enthalpy reported in the textbook On the other hand it is important to note that my experiment also yielded a standard deviation of 5 kJmol meaning that there was considerable range of magnitudes for the enthalpy of neutralization and the results were not very quotprecisequot or quotconfidentquot According to the standard deviation my actual value could have been below or above the final calculated enthalpy by 5 kJmol which would result in range between 48 and 58 kJmol 6 What is the biggest source of error in the enthalpy of neutralization measurements performed in this experiment 2 pts The biggest source of error for this experiment probably comes from how we measured the intial temperature of HCI During the strong base and strong acid neutralization experiment we measured the inital temperature of HCI slightly differently For the first trial we measured the intial temperature of the HCI inside a glass beaker Contrastingly for the second trial we measured the intial temperature inside the calorimeter cup set on the counter The effect of measuring the initial temperatures this way is that the first trial will most likely have a higher initial temperature than the second trial which is consistent with our measurements This kind of effect would result because of the differing heat capacities of the glass beaker and the calorimeter cup Because the heat capacity of glass is higher than the heat capacity of calorimeter cup inner cup coming in contact with the cold countertop would have a had a less of an impact on the glass beaker compared to the calorimeter cup Essentially the cool countertop probably lowered the temperature of the HCI as it sat inside the glass beaker or calorimeter cup but to a greater extent for the calorimeter cup 7 What if any is the effect of acid strength on the enthalpy of neutralization 2 pts According to the outcomes of our experiment the magnitude of the enthalpy of a strong acid and strong base neutralization is lower than the enthalpy of the neutralization of a strong base and weak acid Therefore as the acid strength increases the magnitude of the enthalpy decreases This contradicts the theoretical outcome of the experiment where with an increase in acid strength there should have been an increase in the magnitude of the enthalpy Theoretically although a strong acid and strong base neutralization would create an insignificant excess amount of water molecules compared to that of a strong base and weak acid neutralization a strong base and weak acid neutralization would also utilize some of the energy released from the neutralization for the ionization of it conjugate base As a result the magnitude of the enthalpy of the neutralization of a strong acid would be higher than the enthalpy of neutralization of a weak acid 8 Suppose your thermometer is off by 15 C C ie it reads values that are 15 0C higher How would this affect the results in this experiment 2 pts If the thermometer consistently reads values that are higher there should be no effect on the experiment because the enthalpies are determined by a change in the temperature which will not be affected if both the initial and final temperature are higher by the same magnitude On the other hand if only the initial values are higher than the actual the change in temperature would decrease thereby decreasing the change in the enthalpy Contrastingly if the only the final values are higher than the actual the change in temperature would increase thereby increasing the change in enthalpy Laboratory Waste Evaluation 1 pt Laboratory waste is considered anything generated during an experiment that is disposed of down the sewer drain thrown in the garbage collected in a container for disposal by the UW Environmental Health amp Safety department or released into the environment Based on the written lab procedure and your actions during the lab list the identity and approximate amount mass or volume of waste that you generated while performing this experiment 200 mL of DI water 2 paper towels 2 kim wipes 1 disposable pipet 200 mL of DI water 2 ice cubes 100 mL of 05 M HCI 200 mL of 05 M NaOH 100 mL of acetic acid 200 ml of DI water 91 grams of MgSO4 200 ml of DI water 204 grams of MgSO4 7H2O 500 ml of regular water
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