Data, Calculations, and Graphs

NAME: QUIZ SECTION: Note: All sections of this report must be typed DATA, CALCULATIONS, AND GRAPHS Part I. Fractional Crystallization of KNO3 with (NH4)2Fe(SO4)2·6H2O Impurity A. Starting Components (Fract. Crystallization #0) Step 3: Mixture before first crystallization mass KNO3 mass (NH4) 2Fe(SO4) 2.6H2O Total mass of the sample mixture % Impurity (i.e., % Fe compound in the mixture)* *(This is your % impurity for Fract. Crystallization # 0) 4.509 0.507 5.016 10.11 g g g % Fract. Crystallization #1 Step 7: mass of dry filter paper + watch glass 31.644 g Step 10: mass of KNO3 crystals + filter paper + watch glass 35.204 g mass of KNO3 crystallized 3.660 g % KNO 3 recovered (% of KNO3 in Step A.3.) Step 11: 81.171 % mass of KNO3 crystals to be analyzed for purity in Part I.C 0.100 g B. Fract. Crystallization # 2 (Re-crystallization) Step 5: mass of dry filter paper + watch glass 31.636 g Step 7: mass of KNO3 crystals + filter paper + watch glass 32.460 g mass of KNO3 crystallized 0.774 g % KNO 3 recovered (% of KNO3 in Step A.3.) Step 8: 17.166 % mass of KNO3 crystals to be analyzed for purity in Part I.C Page 2 of 7 0.401 g NAME: QUIZ SECTION: C. Analysis to Determine % Impurity First Crystallization Step 3: Absorbance of the Fe(phen)32+ complex at 510 nm 1.542 Does the absorbance exceed the desired range (0 to 2.0 A)? ____no________ N If so, what dilution factor did you use in order to get the absorbance in the desired range? ______N/A_______ What is your absorbance after dilution? (if applicable) N/A Multiply your absorbance by the dilution factor (if applicable) N/A 1.25E+04 M-1cm-1 Molar Absorptivity of ferroin, e Calculate the molarity of Fe2+ from the absorbance (pathlength = 1 cm) M Type your calculation for molarity of Fe2+ (1 mol ferroin = 1 mol Fe2+) molarity Fe2+=(abs Fe(phen)3 2+) / (molar absorbance ferroin)(1cm) molarity Fe2+ = 1.542 / 1.25E+04 M^-1cm^-1 * 1cm = 1.234E-04 M Volume of ferroin complex solution prepared in Steps C.1. and C.2. Calculate the moles of Fe2+ (moles of Fe2+= moles of (NH4) 2Fe(SO4) 2·6H2O) 0.0100 L 1.23E-06 moles Type your calculation for moles of Fe2+ moles Fe2+ = ([Fe2+])(volume ferroin) moles Fe2+ = (1.234E-04 M)(0.0100L) = 1.234E-06 mol Calculate the molar mass (NH4) 2Fe(SO4) 2·6H2O 392.15 g/mole Calculate grams of (NH4) 2Fe(SO4) 2·6H2O in the crystals 4.84E-04 g Type your calculation for grams of (NH4) 2Fe(SO4) 2·6H2O grams (NH4)2Fe(SO4)2*6H2O = (moles Fe2+)(mm (NH4)2Fe(SO4)2*6H2O) grams = 1.23E-06 mol (392.15 g/mol) = 4.839E-04 g Mass KNO3 crystals analyzed for purity (from Step A.11.) (this cell will autofill) Calculate % mass of (NH4) 2Fe(SO4) 2·6H2O in the crystals (This is your % impurity for Fract. Crystallization # 1) 0.100 g 0.484 % Type your calculation for % mass of (NH4) 2Fe(SO4) 2·6H2O in the crystals. %mass = (mass impurity)/(KNO3 crystal mass) x 100 = (4.84E-04 g / 0.100g) x 100 = 0.4839% Page 3 of 7 NAME: QUIZ SECTION: Second Crystallization Absorbance of the Fe(phen)32+ complex at 510 nm Step 3: 0.923 Does the absorbance exceed the desired range (0 to 2.0 A)? __no__________ If so, what dilution factor did you use in order to get the absorbance in the desired range? ___N/A________ What is your absorbance after dilution? (if applicable) N/A Multiply your absorbance by the dilution factor (if applicable) N/A Molar Absorptivity of ferroin, e Calculate the molarity of Fe2+ from the absorbance (pathlength = 1 cm) 1.25E+04 M-1cm-1 7.38E-05 M Volume of solution prepared in Steps C.1. and C.2. Calculate the moles of Fe2+ (moles of Fe2+= moles of (NH4) 2Fe(SO4) 2·6H2O) 0.0100 L 7.38E-07 moles Calculate the molar mass (NH4) 2Fe(SO4) 2·6H2O) (this cell will autofill) Calculate grams of (NH4) 2Fe(SO4) 2·6H2O in the crystals 392.15 g/mole 2.90E-04 g Mass KNO3 crystals analyzed for purity (from Step B.8.) (this cell will autofill) Calculate % mass of (NH4) 2Fe(SO4) 2·6H2O in the crystals (This is your % impurity for Fract. Crystallization # 2) 0.401 g 0.2895 % Summary: % Impurity as a Function of Cystallization Number Crystallization Number 0 1 2 % Impurity Note: Data is being restated here for ease in plotting. The cells for % impurity will autofill from your entries above. 10.110 0.484 0.2895 % impurity v. Crystallization Number 12.000 10.000 % impurity 8.000 6.000 4.000 2.000 0.000 0 0.5 1 1.5 2 2.5 Crystallization Number Part I Results and Discussion Q1.Do your results indicate that fractional crystallization works? Why or why not? yes, they do because the graph shows a non linear decrease in % impurity with each crystalization. The first one recovered 0.484% and the second one recovered 0.2895%. It also shows the % impiurity getting closer and closer to 0 as the crystaliization number increases. Page 4 of 7 NAME: QUIZ SECTION: Summary: % Mass KNO3 Recovered in Crystallization Steps Crystallization Number Mass KNO 3 Crystallized % of Original KNO 3 Mass 0 1 2 4.509 3.66 0.774 100.0 81.17 17.17 Note: Data is being restated here for ease in plotting. For the mass of KNO3 crystallized in crystallization #0, the starting mass of KNO3 you weighed out in Step A.3. will be the mass crystallized, resulting in 100% recovery. The cells for the mass of KNO3 crystallized and % of original KNO3 will autofill from earlier in the report. % KNO3 Recovered v. Crystallization Number 120.0 % of Orignal KNO3 Mass 100.0 80.0 60.0 40.0 20.0 0.0 0 0.5 1 1.5 2 2.5 Crystallization Number Part I Results and Discussion Q2. What is the disadvantage of fractional crystallization? One disadvantage is that KNO3 can be lost during the process of filtering. The first crystallization shows the majoirty of crystals being recovered, with 82% but the second crystallization only recoverd 24% of the original KNO3 mass. Another disadvantage is the amount of time it takes to filter and dry the substance. Page 5 of 7 NAME: QUIZ SECTION: Part II. Determining the Solubility Curve of KNO3 Cryst. Temp, oC Solubility (in g KNO 3 per 100 g water) Molality KNO3 (mol/kg) Ksp (using molality) 1/T (in K) ln Ksp 2.000 18.3 40.00 3.956 15.65 0.00343 2.7505 3.000 30.7 60.00 5.935 35.22 0.00329 3.5616 4.000 42.7 80.00 7.913 62.62 0.00317 4.1371 5.000 54.1 100.00 9.891 97.83 0.00306 4.5832 6.000 41.7 120.00 11.87 140.9 0.00318 4.9481 7.000 55.5 140.00 13.85 191.8 0.00304 5.2565 Grams KNO3 Type your calculation for solubility (in grams KNO3/100 grams water) using the data for the ~2.0 gram sample. solubility = 2.00g KNO3/ 5g H2O = x g KNO3/ 100g H2O x = 40.0g KNO3 Type your calculation for molality of KNO3 (in mol KNO3/kg water) using the data for the ~2.0 gram sample. molality= moles KNO3/ kg water = (2.00g * 101.1032 g/mol) /0.005 kg = 3.96mol/kg Type your calculation for Ksp (using the molality values) using the data for the ~2.0 gram sample. Ksp = [K+][NO3 -] = (3.96mol/kg)^2 = 15.7 [K+]=[NO3 -] KNO3 Solubility v. Temperature KNO3 Solubility(g KNO3/ 100g H2O) 160.00 140.00 120.00 100.00 80.00 60.00 40.00 20.00 0.00 0.0 10.0 20.0 30.0 Temperature (C) Page 6 of 7 40.0 50.0 60.0 NAME: QUIZ SECTION: (Data autofills here for ease of plotting) P a ln(Ksp) v/ 1/T 6.0000 B 5.0000 ln(KSP) 4.0000 1/T (in K) ln Ksp 0.00343 2.7505 0.00329 3.5616 0.00317 4.1371 0.00306 4.5832 0.00318 4.9481 0.00304 5.2565 3.0000 y = -5792x + 22.704 R² = 0.8424 2.0000 1.0000 0.0000 0.00300 0.00305 0.00310 0.00315 0.00320 0.00325 0.00330 0.00335 0.00340 0.00345 0.00350 1/T (K) slope -5.79E+03 K DHo Soln 4.82E+01 kJ/mol y-intercept 22.70 D SoSoln 188.7 J·mol-1·K-1 Type your calculations for DHsoln and DSsoln. ∆Hsoln = (-5792K^-1)(-8.314 J/mol*K)(1 kJ/1000J) = 48.15 kJ/mol ∆Ssoln = (22.70)(8.314 J/mol*K) = 188.73 J/mol*K Part II Results and Discussion Q1. The literature value for the enthalpy of solution of KNO 3 is 34.89 kJ/mol and the entropy of solution of KNO3 is 248 J·mol-1·K-1. How do your values compare? Calculate the % error for both the enthalpy and entropy. enthalpy: [(34.89-48.15)/34.89]x100 = 38.0% entropy: [(248-188.7)/248]x100 = 23.91% My value for enthalpy is higher than literature value and my value for entropy is lower than the literature value. Q2. Discuss reasonable source of error for both the measured values of enthalpy and entropy. The biggest source of error was a spill that occurred when transferring the solution between the first and second crystallization. This most likely resulted in even more KNO3 being "lost" than actuallt was, impacting the enthalpy and entropy calculations. Another possible source of error was inaccurate temperature observations and calculations. It is possible that crystallization happened before it was noticed, raising the temperature. It is also possible the temperature reading itself wasn't accurate on the thermometer. Page 7 of 7