mohr method

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Title: Determination of chloride by the Mohr Method
Objective: To determine chloride by using Mohr Method.
Introduction:
The Mohr method is the method used to determine the chloride ion concentration of a solution by titration with silver nitrate. As the silver nitrate solution is slowly added, a precipitate of silver chloride forms.
Ag+ + Cl-  AgCl(s) (Ksp for AgCl is 1.810-10)
The chloride ion (Cl-) is an important anion found in solids and solutions. Chloride is the predominant anion of sea water with a molarity of approximately 0.54M. Therefore, it is an essential component of fluid systems in the body. In this experiment, the amount of chloride ion in an unknown sample of water need to be determined by using the Mohr method , which relies on the solubility differences of two anions and the titration endpoint of a precipitate. When all the chloride ions are precipitated, the end point of the titration occurs. Then, a red-brown precipitate of silver chromate the additional silver ions react with the chromate ions of the indicator, potassium chromate, to form: (Ksp for Ag2CrO4 is 910-12 )

Procedure:
A. Standardization of 0.1 M AgNO3 solution
0.2500 g portions of NaCl was weighed into Erlenmeyer flasks and about 100 mL of distilled water was dissolved in. Small quantities of NaHCO3 was added in order to adjust the pH of the solutions until effervescence ceased. About 2 mL of K2Cr04 was added and the solution was titrated with 0.1 M AgNO3 solution to the first permanent appearance of red Ag2Cr2O4.
B. Determination of Cl- in solid sample
The unknown was dried at 110 for 1 hour and cooled in a desiccator. Individual samples were weighed into each of three 250 mL Erlenmeyer flasks and dissolved in about 100 mL of distilled water. Small quantities of NaHCO3 was added until effervescence ceased. About 2 mL of K2CrO4 was introduced and the solution was titrated to the first



References: 1. UDEC 1224 Chemistry Laboratory II Prelab Manual, Experiment 8: Determination of chloride by the Mohr Method. 2. Determination of chloride by the Mohr Method. By Dr. Deniz Korkmaz. Retrieved on 23 July 2014. http://academic.brooklyn.cuny.edu/esl/gonsalves/tutorials/Writing_a_Lab_Report/xPrecipitation%20Titration%20edited%203.pdf 3. Determination of chloride by the Mohr Method. Retrieved on 23 July 2014. http://rwsl.nic.bc.ca/Chemistry/Lab_2/PDF/CHEM-Sem2-Lab6.pdf

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