Experiment 4: Comparison of Two Chloride Determinations
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Experiment 4: Comparison of Two Chloride Determinations Purpose: The purpose of this lab was to compare two “wet” chemical techniques to analyze an unknown chloride sample. These two techniques were a volumetric chloride determination and a gravimetric determination. Reactions: π΄πππ3 + πΆπ − → π΄ππΆπ(π ) + ππ3− π΄ππΆπ(π ) → π΄π+ + πΆπ − Procedure: Volumetric Chloride 1. 2. 3. 4. 5. 6. 7. Accurately weigh about 4g of AgNO3 and dissolve in 100mL distilled water. Quantitatively transfer the solution to a 200mL volumetric flask. Dilute and follow by mixing. Accurately weight about 0.1g of unknown chloride into 125mL Erlenmeyer flasks. Dissolve the three samples into 50mL of water. Add 0.03g dextrin and 5 drops of dichlorofluoroscein indicator. Titrate with silver nitrate solution. Gravimetric Chloride 1. Prepare three Gooch crucibles by cleaning with approximately 0.1M HNO3 and then approximately 0.1M NH3. 2. Follow with distilled water 3. Dry for one hour in a 120°C oven. 4. Dissolve each of three samples (0.2g of unknown) in a 400mL beaker with 150mL of distilled water. 5. Add 1mL of 6M HNO3. 6. Add silver nitrate solution to precipitate the unknown. 7. Heat solution a hot plate, but not boiling, and frequently stir until clear. 8. Filter samples through weighed Gooch crucibles with mild suction. 9. Use warm approximately 0.1M HNO3 to wash five times. Rinse with distilled water. 10. Dry crucibles in oven for two hours. 11. Record mass and calculate percent chloride. Data: ο· Grams of AgNO3: 4.0229g Volumetric Data Amount 1 Amount 2 Unknown Chloride 0.1010 g 0.1007 g Dextrin 0.0305 g 0.0306 g AgNO3 Added 14.2 mL 13.8 mL Amount of Final Cl 0.0596 g 0.0579 g % Cl 58.99% 57.5% ο· Average % of Cl in unknown: 58.26% ο· Standard Deviation: 58.26 ± 0.746 Amount 3 0.1000 g 0.0303 g 13.9 mL 0.0583 g 58.3% Gravimetric Data Amount 1 Initial Weight 33.6852 g Chloride Unknown 0.2003 g Silver Nitrate Added 27.80 mL Final Crucible Weight 34.1400 g Weight of Unknown 0.4548 g Mass Cl 0.1125 g % Cl 56.17% ο· Average % of Cl in unknown: 56.44% ο· Standard Deviation: 56.44 ± 0.584 Sample 1 2 3 Vol. Determination % 58.99% 57.50% 58.30% Amount 2 35.1401 g 0.2005 g 27.84 mL 35.6028 g 0.4627 g 0.1145 g 57.11% Amount 3 35.0341 g 0.2004 g 27.80 mL 35.4881 g 0.4540 g 0.1123 g 56.04 % Grav. Determination % 56.17% 57.11% 56.04% Difference 2.82 0.39 2.26 Difference Mean 1.823 Std. Deviation 1.272 t-calculated 3.510 Calculations: Volumetric Chloride Calculation: ππΏ π΄πππ3 × π π΄πππ3 1 πππ π΄πππ3 1 πππ πΆπ − 35.435π πΆπ − × × × 200ππΏ π΄πππ3 169.8682π π΄πππ3 1 πππ π΄πππ3 1 πππ πΆπ − 14.2ππΏ π΄πππ3 × 4.0029π π΄πππ3 1 πππ π΄πππ3 1 πππ πΆπ − 35.435π πΆπ − × × × = 0.0596π πΆπ − 200ππΏ π΄πππ3 169.8682π π΄πππ3 1 πππ π΄πππ3 1 πππ πΆπ − Percent Cl- in Unknown: π πΆπ − × 100% π ππππππ€π 0.0596π πΆπ − × 100% = 58.99% 0.1010π ππππππ€π Gravimetric Amount of AgNO3 Solution Needed: π π’πππππ€π π₯ π΄π£π % π₯ 1 πππ πΆπ − 1 πππ π΄πππ3 200 ππΏ π΄πππ3 169.8682 π π΄πππ3 π₯ π₯ π₯ − 35.435 π πΆπ 1 πππ πΆπ − 1 πππ π΄πππ3 1 πππ π΄πππ3 0.2003π π’πππππ€π π₯ 0.5826 π₯ 1 πππ πΆπ − 1 πππ π΄πππ3 200 ππΏ π΄πππ3 169.8682 π π΄πππ3 π₯ π₯ π₯ = 27.8ππΏ − 35.435 π πΆπ 1 πππ πΆπ − 1 πππ π΄πππ3 1 πππ π΄πππ3 Mass of Cl-: π π΄ππΆπ π₯ 0.4548π π΄ππΆπ π₯ 1 πππ π΄ππΆπ 1 πππ πΆπ 35.435 π πΆπ π₯ π₯ 143.32 π π΄ππΆπ 1 πππ π΄ππΆπ 1 πππ πΆπ 1 πππ π΄ππΆπ 1 πππ πΆπ 35.435 π πΆπ π₯ π₯ = 0.1124π 143.32 π π΄ππΆπ 1 πππ π΄ππΆπ 1 πππ πΆπ Percent Cl- in Unknown: π πΆπ − × 100% π ππππππ€π 0.1124π πΆπ − × 100% = 56.17% 0.2003π ππππππ€π Standard Deviation: ∑(ππ − πΜ ) π=√ π−1 T-Calculated: ο· Ttable= 2.776 for 95% confidence interval π‘ππππ = πΜ √π π Conclusion: For this lab, two techniques were used to analyze an unknown chloride sample. Our data showed a 58.26 ± 0.746% for the volumetric analysis and a 56.44 ± 0.584% for the gravimetric analysis. We calculated the t value for both techniques and found that our results were greater than the t value from the table. This means the results were significantly different. There were several possible sources of error for this experiment. For the volumetric analysis, there is a chance we overshot the titration by adding to much titrant. This error could be corrected by titrating drop by drop. That, however, is not very time efficient. For the gravimetric analysis, we could have lost some product every time we switched glassware. This error could be corrected by having as few glassware transfers as possible.
