Report 4 - 1 Volumetric Determination of Impure Sodium...

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Volumetric Determination of Impure Sodium CarbonateCHM3120C-903Vincent Gallo U61917512Shane SpiersFebruary 22nd20161
I. IntroductionAn acid-base titration is a volumetric procedure conducted by analysts in order to determine the exact concentration of an acid or base. In most cases, a volume of acid or base of known concentration serves as the titrant, and is reacted with the sample containing the unknown until the equivalence point is reached. With respect to acid-base titrations, the equivalence point of the chemical reaction occurs when there are equivalent quantities of acid and base in a mixture. Therefore,the moles of base are equivalent to the moles of acid. In this experiment, HCl will serve as the titrant, because its concentration is known (.1202M). It will then be added drop wise to a crude sodium carbonate mixture, or, “soda ash” in order to determine the percent mass of carbonate in the sample. This specific reaction produces sodium chloride and carbonic acid. In the second part of the reaction, carbonic acid decomposes to produce carbon dioxide and water. Because this reaction involves two different parts, two indicators will be used, namely, phenolphthalein and bromocresol green. Phenolphthalein, with a pH range of 8.3-10 is used in the preliminary part of the titration because the soda ash is very alkaline (~pH of 10). The need for a second indicator stems from how much HCl needs to be added to the solution in order to neutralize it. Once the phenolphthalein turns clear, there is no way to track the reaction’s progression. Therefore, as the reaction becomes more acidic, the pH will decrease, and the secondindicator, bromocresol green (pH range 3.8-5.5) can be used to track the reaction’s progression. Bromocresol green’s color indication goes from blue, to teal to yellow. In this experiment, the first part of the reaction will be allowed to go until the 2
premature endpoint is reacted (teal). At this point, the reaction mixture contains a large amount of CO2, and little bicarbonate. The CO2 is dispelled via heat because it’s presence in the mixture changes the color of the indicator, and it is not the desired product. After the CO2is released as a gas, the reaction mixture will return to its blue

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