Report 2 - The Gravimetric Determination of Chloride in a...

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The Gravimetric Determination of Chloride in a Soluble Sample CHM3120C-903 Vincent Gallo U61917512 Shane Spiers February 8 th 2016
I. Introduction The chloride content of a crystalline powder can be determined when the chloride is precipitated from the solution as silver chloride. Gravimetric analysis of the precipitate can be used so that the percent mass of the chloride in the precipitate can be calculated. The chloride percent mass calculated for the precipitate should be identical to the chloride percent mass in the original sample. The unknown sample will be dissolved so that the chloride ions can be reacted with silver ions, and thus, form the insoluble (K sp = 1.8 x 10 -10 ) silver chloride precipitate. Silver chloride forms first as a colloid, which is a dissolved particle with an extremely small diameter, preventing precipitation. With heat, the small crystallites will come together to form larger crystals (coagulation) and fall out of solution. Nitric acid prevents peptization during washing, which is the conversion of precipitate to colloidal particles. Upon obtaining the silver chloride, it is important to note any violet color in the precipitate. The color is caused by elemental silver, and is a sign of photodecomposition. If this occurs, chlorine will be lost as gas. It is important that direct light is prevented from interacting with the final product. If the precipitation reaction is done correctly and carefully, precision within four trials will be obtained, and the results will not vary from the actual Cl - percent mass. Again, ideally, the percent mass of chlorine in the precipitate will be identical to that of the starting material. Results with a percent error of less than 5% are evidence of a successful reaction, given the practicality of the laboratory in which the experiment is to be completed.
II. Experimental Procedure PART A A weighing paper was used to measure out four different .225g samples of the unknown and then each was quantitatively transferred into its own 250ml beaker. After that, the sample was dissolved in 100ml of distilled water and this step was followed with adding 2ml of 6 M nitric acid. While stirring, 15ml of silver nitrate

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