Orlando 1 Quantitative Analytical Chemistry Joseph Orlando Lab #4: Comparison of Two Chloride Determinations Purpose: In this experiment we analyzed an unknown chloride sample via two different “wet” chemical techniques; a volumetric chloride determination and a gravimetric determination. After the experimental data was obtained, the two methods were statistically compared. Cl- + AgNO3 -----> AgCl (s) + NO3AgCl (s) -----> Ag+ + ClProcedure: Volumetric Chloride Determination 1. Weigh ~4g AgNO3 and dissolve in 100mL distilled H2O. Transfer solution to a 200mL volumetric flask and dilute and mix. 2. Into a 125mL Erlenmeyer flask weigh out 0.1g of unknown chloride. Dissolve three samples in 50mL H2O. Add 0.03g dextrin and 5 drops dichlorofluorescein indicator. Titrate with silver nitrate solution to a pink endpoint. 3. Calculate percent chloride in the sample. Gravimetric Chloride Determination 1. Clean three gooch crucibles with 0.1 M HNO3 then with 0.1 M NH3. Follow with a distilled H2O wash then dry for an hour in a 120° C oven. Fit each crucible with a glass fiber filter. 2. Dissolve three samples (0.2g) in a 400mL beaker with 150mL H2O, add 1mL of 6M HNO3. 3. Add enough silver nitrate to precipitate unknown chloride. Heat on a hot plate without boiling and frequent stirring. 4. Filter samples through gooch crucibles with suction. Use warm 0.1M HNO3 to was precipitate. 5 washes suggested. Rinse with distilled H2O. 5. Dry crucibles and precipitate in a 120°C oven for two hours, weigh. Data: Volumetric Determination Mass (g) of dextrin added Volume (L) of AgNO3 titrated Percent (%) Chloride Trial #1 Mass (g) of Unknown Chloride added 0.1157 0.0308 0.01472 54.70% Trial #2 0.1087 0.0305 0.01449 57.37% Orlando 2 Trial #3 0.1045 0.0296 0.01369 56.38% Average 0.1096 0.3030 0.01430 56.15% Gravimetric Determination Mass (g) of Product 0.4808 Mass (g) Cl Trial #1 Mass (g) Unknown Sample 0.2299 0.1189 Percent (%) Chloride 51.78% Trial #2 0.2350 0.5159 0.1276 54.30% Trial #3 0.2051 0.4358 0.1077 52.51% Average 0.2233 0.4775 0.1181 53.41% Student’s T-test Gravimetric Determination Cl- % 51.78% Difference Trial #1 Volumetric Determination Cl- % 54.70% Trial #2 57.37% 54.30% 3.07 Trial #3 56.38% 52.51% 3.87 2.98 Average 3.31 Standard Deviation 0.499 tcalculated 3.04 𝑡𝑡𝑎𝑏𝑙𝑒 4.303 (at 95% Confidence Interval) Equations: Mass of Cl-final: amount of 𝐴𝑔𝑁𝑂3 titrated × 4.0126 AgNO3 1 𝑚𝑜𝑙 AgNO3 1 𝑚𝑜𝑙 𝐶𝑙 35.45 𝑔 𝐶𝑙 × × × =mass of Cl 200 mL AgNO3 169.868 𝑔 AgNO3 1 𝑚𝑜𝑙 AgNO3 1 𝑚𝑜𝑙 𝐶𝑙 Percent Cl- in Unknown: Orlando 3 𝑚𝑎𝑠𝑠 𝑜𝑓𝐶𝑙 × 100% = 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑐ℎ𝑙𝑜𝑟𝑖𝑑𝑒 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 mass of unknown Cl used Gravimetric Determination Mass of Cl-final: mass of AgCl× 1 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙 1 𝑚𝑜𝑙 𝐶𝑙 35.45 𝑔 𝐶𝑙 × × = 𝑚𝑎𝑠𝑠 𝑜𝑓𝐶𝑙 143.32 𝑔 𝐴𝑔𝐶𝑙 1 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙 1 𝑚𝑜𝑙 𝐶𝑙 % Cl- in Unknown: mass of Cl ×100% = percent chloride in sample mass of unknown sample used Student’s t Test: 𝑡𝑐𝑎𝑙𝑐 = |𝑑̅| ×√𝑛 𝑠 Conclusion The average chloride % that was calculated from the volumetric method was 56.15% and 53.41% from the gravimetric method. At the 95% Confidence interval with 2 degrees of freedom the 𝑡𝑡𝑎𝑏𝑙𝑒 value is 4.303. Using the student’s T-test it was calculated that T value for the two different methods was 3.04. Because the 𝑡𝑐𝑎𝑙𝑐 value is less than the 𝑡𝑡𝑎𝑏𝑙𝑒 value we can say that there is less than a 95% chance that the data from the two methods, volumetric and gravimetric, are different. This experiment proved to be an overall success. Post Lab Questions: 1. Discuss appropriate procedural changes which could improve the error in both experiments. The main procedural change would involve the drying process in the furnace for two hours. I believe that the product was not allowed to fully dry and therefore this altered the data that was obtained.