Chemistry 0330 Laboratory Report 4Chemistry 0330 Laboratory Report 4, Exams of Nursing

Download Chemistry 0330 Laboratory Report 4Chemistry 0330 Laboratory Report 4 and more Exams Nursing in PDF only on Docsity! 1 EXPERIMENT 4 Chemistry 0330 Laboratory Report 4 Experimental Error Analysis: Heat Capacity of Unknown Metal and Recovering Reaction Products PART A Questions About the Experiment (Please Answer the following questions using your lab manual, prelab lecture video, and the video entitled “Lab 2 - Error Analysis”) 1. Suppose you are running an experiment using parts 1 and 2 of the lab manual. a.After moving the thermometer from the hot water bath to the calorimeter, you see the reading of the thermometer lower before it rises. Why might this be? If you record the temperature (Tmixture) without waiting for the temperature to rise, how will your results be affected? This is because the heat from the hot water is released before an equilibrium temperature is reached after is becomes acclimated to the calorimeter. If you record this temperature type will not get the right temperature. b. In Part 1, why do you repeat steps 1-9? What might be some other ways to minimize possible error? You repeat them to try and lower the chance you make an error in the process by redoing it and making sure you didn’t miss any part of the process. To minimize possible error you can make sure you thoroughly read directions and check your work constantly to make sure it is right. This will also help determine the precision. And accuracy. c. Step 9 in part 1 of the lab manual states that Tmixture is the highest temperature obtained once the heated metal cylinder is placed into the 2 calorimeter. Do you expect Tmixture to be closer to the initial temperature of the metal (Tmetal) or the initial temperature 5 hose, and pour the liquid out of the filter flask into the original beaker. f. What does it mean if the mass of your crystals in Part 2 after vacuum filtration is higher than the expected value for the mass? How can this problem be solved? This means that your filter papers were laid incorrectly and the collection of the crystals were therefore not the expected value for the mass. This can be fixed by properly setting up your filter papers and re- cover everything to get the correct collection of crystals. PART B Experimental Error Analysis – Specific Heat Capacity of an Unknown Metal Note: Below is the data from a sample trial. Use this when answering the questions below. Show all work for calculations. mcylinde r1 (g) mcylinde r2 (g) mcylinde r3 (g) mcalorimeter (g) mw+cal (g) Vwate r (mL Twate r (℃) Tmet al (℃) Tmixtur e (℃) 6 ) 50.325 4 50.325 5 50.325 5 3.4838 104.221 9 99.7 23.1 101.2 30.8 7 1. a. Restate the three masses of the metal determined in step #1 of the procedure (including the absolute and percent uncertainty). 1) 50.3254 +/- 0.0001 (0.0002%) 2) 50.3255 +/- 0.0001 (0.0002%) 3) 50.3255 +/- 0.0001 (0.0002%) b. Calculate the average mass of the metal (including the absolute and percent uncertainty). Average mass = 50.3255 +/- 0.0001 (0.0002%) 2. a. Calculate the mass of the water in the calorimeter (including the absolute and percent uncertainty). Mass of water = 100.7381g +/- 0.0001 (0.0001/100.7381 = 9.926 x 10^-7%) b. The density of water is 1.00 g/mL. Using the exact volume of the water measured in step #5 of the procedure, find the mass of the water (including the absolute and percent uncertainty). 1.00g/mL x 100mL +/- 0.5 mL = 100g +/- 0.5g 0.5/100 = .5% uncertainty c. Which method of finding the mass of the water (volume v.s. weight) has less experimental error? Which method is more precise and which one is more accurate? when repetitive measurements are made? The method of using the weight is more precise because there is less 10 4. a. Calculate ΔTwater, the increase in temperature of the water after the metal is placed in it (including the absolute and percent uncertainty). • ΔTwater = 7.7 degrees celcius +/- .2 degrees C (2.6% uncertainty) b. Calculate ΔTmetal, the decrease in temperature of the metal after it is placed in the calorimeter (including the absolute and percent uncertainty). ΔTmetal = _-78.1 degrees C +/- 0.2 degrees C (.26% uncertainty) c. Are the above values of ΔTwater and ΔTmetal similar? Should they be the same? They are not similar and they should not be the same. 5. a. Calculate the amount of heat, in Joules, absorbed by the water (Qwater) in the calorimeter (include the absolute and percent uncertainty). Use 4.18 J/(g•oC) as the specific heat capacity of water (Cwater). \ Q = mxcxdT = 100.7381g +/- .0001g (4.18 J/(gxC))(7.7 C +/- .2) .0001/100.7381 = 0.0001% + 0.2/7.7 = 2.6% = 2.6001 % = 3242.4 J +/- (84.304 J) (2.6%) 11 b. Determine the identity of the metal by calculating its specific heat capacity and 12 comparing it with the values for the metals listed in Table 1 of the lab manual. For mmetal, use the result from question #1. = (50.3255 +/- 0.0001) c. Using the literature values listed in Table 1 of the lab manual, calculate the percent error of your experimentally determined value for the specific heat capacity. ( | heat capacity – specific heat of metal | / specific heat of metal) x100 = percent error d. Suggest two possible sources of the observed percent error. Uncertainty in measuring devices and error because the heat loss in the calorimeter. 6. A piece of metallic gold with a mass of 38.5700 g was placed in 49.7 mL of ethanol in a graduated cylinder. The ethanol level was observed to rise to 51.7 mL. Which density value below is reported with the correct number of significant figures? Explain your choice. a. 19.29 g/mL b. 19.3 g/mL c. 19.285 g/mL d. 1.9 x101 g/mL 38.5700/(51.7-49.7) = 19.3 Because its dividing it is smallest number of sig figs 15 Mass of precipitate Beaker #1 0.1305 g +/- .0002g Beaker #2 0.1415 g +/- .0002g 2. Complete the table and add absolute uncertainties, where appropriate. CaCl2 Na2CO3 Concentration used 0.5 M 0.4M Volume used beaker #1 4.0 mL +/- 0.1mL 3.5 mL +/- mL Volume used beaker #2 3.0 mL +/- 0.1mL 4.5 mL +/- mL 2. Restate the balanced chemical equations for the reaction of CaCl2 with Na2CO3 (molecular and net ionic equations) CaCl2 (aq) + Na2CO3 (aq)  2NaCl (aq) + CaCO3 (g) Ca ^2+ (aq) + 2Cl^- (aq) + 2Na^+ (aq) + CO3^2- (aq)  CaCO3 (s) + 2NaCl (aq) 4. Determine the limiting reactant, theoretical yield, and actual yield. Show the work. Beaker #1 Beaker #2 Limiting Reactant: Na2CO3 Limiting Reactant: CaCl2 Theoretical Yield: 0.0014 mol CaCO3 Theoretical Yield: 0.0015 mol CaCO3 Actual Yield: 0.001245 mol CaCO3Actual Yield: _0.0026 mol CaCO3 4mL x 1L/ 1000mL x .5mol/1L = 0.002 mol CaCl2 3.5mL x 1L/1000mL x .4 mol/1L = 0.0014 mol Na2CO3 0.1246 +/- 0.0002 g x 1mol/100.0869 g = 0.001245 mol 3mL x 1L/ 1000mL x .5mol/1L = 0.0015 mol CaCl2 4.5 mL x 1L/1000mL x .4 mol/1L = 0.0018 mol Na2CO3 0.2595 +/- .0002g x 1/100.0869 = 0.00259 mol 16 5. Calculate the experimental percent errors between your experimental and the theoretical yields (show the work). Explain possible sources of errors. Beaker #1 Beaker #2 Percent Error in Yield: _11.07% Percent Error in Yield: 72.6% ((0.001245-0.0014)/0.0014) x100 ((0.00259-0.0015)/0.0015) x100 = = 11.07 72.6 Explanation of Possible Sources of Errors: - Inaccurate amount of solutions added - The vacuum wasn’t working properly and did not completely dry the papers - The filters were not put on properly - Could have not counted all the precipitate or not given reaction enough time to produce all the precipitate