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We are determining the concentration of halides (%Cl). There are many methods to determine the concentration of a halide.

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Introduction

Analytical Chemistry 2080 Experiment #3: Determination of Halides. Name: Elizabeth Conway TA: Anna Date performed: Wednesday, October 3rd 2007 Wednesday, October 10th 2007 Wednesday, October 17th 2007 Date Due: Wednesday, October 24th 2007 Unknown #: 363 Experiment #3: Determination of Halides. Introduction: We are determining the concentration of halides (%Cl). There are many methods to determine the concentration of a halide. Scientists have been coming up with new ways of method determination for hundreds of years. In this lab we used three different methods of determination. These three methods are Volumetric determination, Gravimetric determination and Potentiometric determination. After finding our chloride concentration we will then compare these three methods and determine which best fits of experiment. In the Volumetric determination, we are using two different methods; the farjans method and the Mohr method. Both of these methods are the same in that chloride is precipitated by means of silver nitrate but they use different indicators. While collecting the data from the lab you can then determine the equivalence point, which is when the amount of AgNO3 is added is equal to the amount of analyte present in to unknown solution. Since the acid is a monoprotic acid, there is only one equivalence point. In Gravimetric determination, we are using the quantitative determination of an analyte based on the mass of a solid. Therefore, the analyte must first be changed into a solid by precipitation, which is then filtered, dried several times and finally weighed. Calculated by the mass of the precipitate and its chemical composition, the amount of analyte can be determined. In Potentiometric determination, which is a better way of detection to find the end-point or equivalence point, we do the titration of the unknown but with no indicator, instead we use an indicator electrode that is submersed in the solution as well as a reference electrode made of saturated calomel electrode (SCE). ...read more.

Middle

Original Weight (g) Weight after 1st drying (g) Weight after 2nd drying (g) Weight after 3rd drying (g) 138 0.2091 29.5305 � 0.00005 30.0158 � 0.00005 30.0165 � 0.00005 30.0167 � 0.00005 136 0.1959 29.8559 � 0.00005 30.3072 � 0.00005 30.3066 � 0.00005 30.3064 � 0.00005 137 0.2072 29.6378 � 0.00005 30.1184 � 0.00005 30.1186 � 0.00005 30.1187 � 0.00005 Part C Table 2.14: Potentiometric Titrations Weight of unknown: 1.0038 g Titration #1 Potential (mV) Titrant added (mL) -033 0.079 -028 1.00 -027 1.93 -026 3.01 -025 4.06 -023 5.04 -023 6.10 -022 7.09 -020 8.21 -019 9.09 -017 10.10 -015 11.11 -013 12.08 -013 13.06 -011 14.04 -009 15.30 -008 16.28 -006 17.11 -004 18.03 -002 19.05 000 20.19 002 21.09 005 22.10 007 23.04 011 24.05 014 25.04 018 26.11 021 27.12 025 28.09 032 28.95 036 30.09 040 30.18 043 30.24 045 30.33 045 30.42 049 30.79 051 30.98 053 31.51 057 31.68 068 32.31 075 32.42 081 32.51 100 32.69 140 32.78 219 32.99 233 33.11 240 33.19 250 33.31 261 33.43 267 33.60 272 33.68 280 33.94 284 34.02 293 34.13 295 34.31 297 34.49 299 34.71 303 35.02 Titration #2 Potential (mV) Titrant added (mL) -036 0.11 -033 0.98 -029 2.04 -027 2.99 -027 4.02 -025 5.21 -024 6.31 -023 7.29 -022 8.00 -020 9.08 -018 10.10 -017 11.10 -014 12.49 -014 13.21 -013 14.20 -012 15.32 -010 16.49 -007 17.53 -005 18.61 -003 19.52 -001 20.56 002 21.54 005 22.58 009 23.67 013 24.61 017 25.70 021 26.74 027 27.76 031 28.69 036 29.51 049 30.54 068 31.50 075 31.73 083 31.94 092 32.02 99 32.11 110 32.24 137 32.33 176 32.41 224 32.52 246 32.66 262 32.77 270 32.92 276 33.06 280 33.14 284 33.22 287 33.39 290 33.51 292 33.62 295 33.71 297 33.91 300 34.12 304 34.51 309 35.00 Titration #3 Potential (mV) ...read more.

Conclusion

In my personal opinion I think that in looking at the two different plots in part C, plotting (delta E/deltaV) vs. Volume is a better method of determining the end-point because it is more visual as in the high spike is the equivalence point. Instead of looking at the plot E vs. V and determining where the equivalence point by looking for the most vertical area of the plot, which has room for a lot of error. If I was required to select an accurate and precise method for future chloride analysis, I would have to choose the gravimetric method. I would choose this method because it is a method with less room for error. Unfortunately it is very time consuming so to get accurate and precise method that is not too time consuming I would have to then choose the volumetric method. Conclusion After using three different methods for determination of a halide, I have found that by volumetric determination the %Cl is 58.62 � 0.313% with 95% confidence limits of 0.354% for the Fajans method and 57.47 � 0.434% for the Mohr method with 95% confidence limits of 0.492%. In using the paired t-test, I have found that there is no significant difference between the two methods. For Gravimetric determination I have found that the %Cl is 57.27 � 0.339% with 95% confidence limits of 0.383%. And for the Potentiometric determination I have found a %Cl of ____________________ with 95% confidence limits of ___________, I have also plotted E vs. volume (Graph 3.1) and ?E/?V vs. volume (Graph 3.21) for trial #1, and did the preferred method of graphing for trials 2 and 3 (Graph 3.22 and Graph 3.23) for the Potentiometric determination. Reference - http://en.wikipedia.org/wiki/Gravimetric_analysis - http://en.wikipedia.org/wiki/Volumetric_analysis - Chemistry - CHEM 2080 4.0, York University, p. 13-20 - http://en.wikipedia.org/wiki/Potentiometric_analysis - ...read more.

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