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Preparation and Standardization of a Silver Nitrate Solution and Argentometric Titration of a Soluble Chloride Makaela Everett October 13, 2020 CHEM2300L – Wednesday A

Abstract The experiment completed was the preparation and standardization of a silver nitrate solution and argentometric titration of a soluble chloride. This was completed to understand the use of precipitation titrations, and to understand the process of standardization for an experiment. One goal was to learn what the process of standardization entails. Also, to perform volumetric and stoichiometric calculations in a volumetric analysis. Plus, to discover the properties a primary standard must possess to be useful. To learn how indicators, work in a precipitation titration, and to understand the chemistry of a precipitation titration. For the standardization was completed through three trials, the AgNO3 solution to be 0.0937 M, the standard deviation of this solution was then found to be 0.01901 M. The precent relative standard deviation and confidence level at 95% were also found to be 20.29% and ±0.02151 M. The final goals were to find the mass and percent of Cl in the unknown sample through three titration trails. The unknown sample of chloride ion found in the bottle labeled number 341 was used for the identification of percent chloride in an unknown sample. The formation of silver chloride was used to find the concentration chloride ions. Chloride was first extracted from the solution in the form of a precipitate. Solubility properties made isolating this particular ion reasonably easy. By implementing the reaction so that it goes to completion, the Cl- ion was reacted with other ions to form an insoluble substance. By the end of the experiment the mass of the silver chloride recovered was determined and with the use of stoichiometry, the chloride content of the new substance was calculated. Three trials were completed to demonstrate accuracy and precision to the experiment. The percent recovered of Cl-by each trial included: 33.45%, 30.01% and 30.12%. Therefore, the precision of the values was close to 100%.

Introduction For this experiment the student learned about the process of standardization and how to perform a precipitation titration. Standardization is the process of determining the exact concentration (molarity) of a solution (2). Titration is the experimentally determined volume of titrate needed to react with all of the analyte in the sample. This volume can be used to find the amount of analyte in a given sample. (1). Indicators are used to help one see when the reaction has reached its endpoint, the indicator used in this experiment is phenolphthalein. Phenolphthalein, an organic compound, is colorless in acidic solution and pink in basic solution. This is important in a chemistry laboratory because it shows when a reaction is completed or has gone to the other side of the reaction in general. Both the standardization and precipitation titration precision are important because when a method is precise a sample will give similar results and the significant difference will be low for the volume of what was titrated and the molarity of what was titrated. Precision characteristics of the titration matter, as well as sensitivity and method stability, need to be validated for each newly developed method (3). This can be used to ensure that your method and instruments produces similar results and values. The purpose of this experiment was to standardize the nitrate solution and then use that standardized solution to find the mass and percent of Cl in an unknown sample through three titration trials. To quantitatively define accuracy and compare to the qualitative treatment of accuracy. To use the F-test to check if variances for two data sets are significantly different. Also, to calculate the pooled standard deviation of a set of data to detect if the results of two data sets are significantly different. The results from this will show how important it is that the indicator is present, and that standardizations and titrations follow procedure and that the calculations are properly performed. In order to analyze the concentration of the standardized AgNO3 and percent Cl- in an unknown sample, six titrations will be performed, and the values will be calculated using stoichiometry and other conversion factors. The total volume used to reach the endpoint of the titration will also display the number of moles used and the Molarity or concentration of the AgNO3 and Cl present.

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Procedure The procedure was carried out according to the experiment hand out Experiment 4: Preparation and Standardization of a Sodium Chloride Solution and Argentometric Titration of a Soluble Chloride

Results The results for the standardization of Silver Nitrate Solution are shown in Table 1 below. The table details the mass of standard NaCl used in grams and the moles of NaCl. Along with the volume of AgNO3 used for the endpoint to be reached, the moles of AgNO3, and the molarity of the AgNO3 solution. The moles and Molarity (M) of AgNO3 were found by using Equation 1. The mean was found to be 0.0937M, standard deviation was 0.01901 M, percent relative data was 20.29%. The 95% confidence limits for the concentration of the silver nitrate solution were found using Equation 2 and was found to be ±0.02151M. Table 1. Standardization of Silver Nitrate Solution

Trial 1 2 3

Mass of Standard NaCl (g) 0.1015 0.1023 0.1021

Mean concentration (M) 0.0937

Moles of Initial Buret NaCl (mol) Reading (mL) 0.001737 0 0.00175 20 0.001747 21.29

Final Buret Reading (mL) 23 38.81 36.69

Volume of AgNO3 to Reach Endpoint (mL) 23 18.81 15.4

Moles of AgNO3 (mol) 3.261 4.944 7.338

Molarity of AgNO3 (M) 0.075 0.093 0.113

Standard deviation (M)

% RDS

Confidence Limit ± (M)

0.01901

20.29

0.02151

The results of the identification of percent chloride in an unknown sample are shown in Table 2 below. The mass of Cl in the unknown was found by using Equation 3, using the calculated concentration of AgNO3 from the previous trials. Then the percent of Cl in the unknown was found using Equation 3. The mean of Cl in the unknown was found to be 31.19%, the standard deviation was found to be 1.953% Cl, and the percent relative standard deviation was found to be 6.262%. The 95% confidence limit for this data was found using Equation 4 and found to be ±2.210.

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Table 2. Identification of percent Chloride in an Unknown Sample

Trial 1 2 3 Mean (%) 31.19

Mass of Unknown Cl (g) 0.1003 0.1025 0.1085

Buret Reading (mL) 0.00 10.05 19.31

Standard Deviation (%) 1.953

Volume of AgNO 3 to Final Buret Mass of Cl in Reading Reach (mL) Endpoint (mL) Unknown (g) 10.10 10.10 0.03355 19.31 9.260 0.03076 29.15 9.840 0.03269 % RSD 6.262

Percent of Cl in Unknown (%) 33.45 30.01 30.12

Confidence Limit ± (%) 2.210

Discussion The purpose of this lab was to standardize AgNO3 and to find the mass and percent of Cl in an unknown sample. Based on the three titration trials, the results show that the average molarity of the standardized AgNO3 was found to be 0.0937M, standard deviation was 0.01901 M, percent relative data was 20.29%. The 95% confidence limits for the concentration of the silver nitrate solution was found to be ±0.02151M. The results also show that the percent of Cl in the unknown sample is 31.19%. The standard deviation also calculated and was found to be 1.953% Cl, and the percent relative standard deviation was found to be 6.262%. The 95% confidence limit for this data was found to be ±2.210%. This shows that there is a very low amount of Cl within this unknown sample. Because the values of the percent of Cl in the unknown are all similar, it can be said that the measurements of the data are precise. However, because the true value of the percent of Cl is not known, it would be impossible to tell weather the data is accurate. The values from this data set show that the measurements made were close to one another, but they did not have high values. It was interesting how the volume of AgNO3 needed to reach the endpoint in the standardization had such a variation, although it was not big, it was more than what was expected from the student. It was also surprising, seeing that the mass and precent of the Cl in the unknow was so low with a average of 31.19%. In most to all cases there is always some ways that errors can occur, the most common one that would apply to this experiment would be human error. The student could have recorded the wrong values or could

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have also recorded values that were past the endpoint for the titration. Other human errors include the possibility that the values are incorrect due to a misreading of the meniscus or miscalculations in determining the moles of AgNO3, mass of Cl in unknown, or the percent of Cl in the unknown. These could have occurred along with some other possible human and instrument errors; in this case it is likely that most of the possible errors came from the student.

Conclusion In this experiment, the overall objective was to understand the use of precipitation titrations, and to understand the process of standardization for an experiment. This was accomplished by the the preparation and standardization of a Nitrate solution and the argentometric titration of a soluble chloride. The Molarity was found by titrating the sample and using the volume needed to reach the endpoint. The results showed the average concentration of the AgNO3 solution to be 0.0937 M, the standard deviation of this solution was then found to be 0.01901 M. The precent relative standard deviation and confidence level at 95% were also found to be 20.29% and ±0.02151 M. Then though three trail titrations and the volume in mL needed to reach the endpoint, the percent of Cl in an unknown sample it was found that the mean of Cl in the unknown sample was an average percentage of 31.19%, the standard deviation was found to be 1.953% Cl, and the percent relative standard deviation was found to be 6.262%. The 95% confidence limit for this data was found ±2.210&. These show how your data could be affected and rejected if you or your instruments are not precise or accurate.

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Sample Calculations a. Concentration of Silver Nitrate ฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀ ฀฀฀฀ ฀฀ ฀฀. ฀฀฀฀ ฀฀฀฀฀฀฀฀ × × × × ฀฀ ฀ ฀ ฀฀฀฀. ฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀ ฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀

= ฀฀฀฀฀฀฀฀฀฀฀฀

฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀฀฀ ฀฀฀฀ ฀฀. ฀฀฀฀ ฀฀฀฀฀฀฀฀ × × × × ฀฀ ฀ ฀ ฀฀฀฀. ฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀ ฀฀฀฀. ฀฀฀฀ ฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀

฀฀฀฀฀฀. ฀฀

= ฀฀. ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀฀฀

฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀ ฀ = ฀฀. ฀฀฀฀฀฀ ฀฀ b. Confidence Level at 95% of Silver Nitrate Concentration

฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ � ฀฀฀฀ � ±= ฀฀ ฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ √฀ ฀ ฀฀. ฀฀฀฀฀฀฀฀ ±

฀฀฀฀฀฀. ฀฀

฀฀. ฀฀฀฀฀฀ × ฀฀. ฀฀฀฀฀฀฀฀฀฀ ฀ √฀

฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ = ±฀฀. ฀฀฀฀฀฀฀฀฀฀ c. Grams and Percent of Chloride of Unknown # ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀ ฀ ×

฀฀ ฀฀฀฀฀฀ ฀฀฀฀+

฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀ ฀

฀฀฀฀.฀฀฀฀฀฀ ฀฀฀฀−

฀฀ ฀฀฀฀฀฀ ฀฀฀฀−

= ฀฀ ฀฀฀฀− Eqn. 3 ×฀฀ ฀฀฀฀฀฀ ฀฀฀฀+ = # ฀฀฀฀฀฀ ฀฀฀฀− × ฀฀฀฀฀฀ ฀฀฀฀−

฀฀ ฀฀฀฀฀฀ ฀฀฀฀+ ฀฀ ฀฀฀฀฀฀ ฀฀฀฀− ฀฀฀฀. ฀฀฀฀฀฀ ฀฀฀฀− −× ฀฀. ฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀ ฀ × × = ฀฀. ฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀ ฀฀฀฀ ฀฀฀฀฀฀ ฀฀฀฀− ฀฀ ฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀ ฀฀฀฀+ = ฀฀. ฀฀฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀−

฀฀ ฀฀฀฀− × ฀฀฀฀฀฀ = % ฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ ฀ ฀ ฀฀. ฀฀฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀− × ฀฀฀฀฀฀ = ฀฀฀฀. ฀฀฀฀% ฀฀฀฀ ฀฀. ฀฀฀฀฀฀฀฀ ฀฀ ฀฀฀฀฀฀฀฀฀฀฀฀฀฀

d. 95% Confidence Interval of Precent Chloride

฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ � ฀฀฀฀ � ±= ฀฀ ฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ √฀ ฀ ฀฀฀฀. ฀฀฀฀ ±

฀฀฀฀฀฀. ฀฀

฀฀. ฀฀฀฀฀฀ × ฀฀. ฀฀฀฀฀฀ √฀

฀

฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀฀ ฀฀฀฀฀฀฀฀฀฀ = ±฀฀. ฀฀฀฀฀฀

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References [1] Harris, D. C. Quantitative Chemical Analysis, 8th ed.; W.H. Freeman: New York, 2010; p 56. [2] Eddy, D. (n.d.). Standardization of Acid and Base Solutions. Retrieved October 15, 2020, from http://www.chem.latech.edu/~deddy/chem104/104Standard.htm [3] Boik, Robert J. "The Fisher‐Pitman permutation test: A non‐robust alternative to the normal theory F test when variances are heterogeneous." British Journal of Mathematical and Statistical Psychology 40.1 (1987): 26-42.

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