analytical lab 4 part 1.pdf - 1 Volumetric Determination of...

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1 Volumetric Determination of Impure Sodium Carbonate Aldo S. Poblete Jr. CHM 3120C Section: 902 TA: Ifeoluwa Ayodeji Lab Partner: Jibran Biag, Cristian Shaver
2 Introduction: For this experiment, a standardized solution of HCl was prepared and utilized in order for unrefined sodium carbonate or soda ash to be titrated (4). The total amount of carbonate in a sample was calculated by knowing the exact amount of sodium carbonate that titrated as well as the volume of the standardized acid used (1). This reaction produced carbonic acid and sodium chloride during the acid-base neutralization step, which will allow for the carbonic acid to be broken down even further into carbon dioxide and water (1). The indicators that were utilized in this analysis demonstrated to be phenolphthalein and bromocresol green; however, one significant difference between the two is that phenolphthalein would have a pH level of 8.3-10, while bromocresol green displays a pH level of 3.8-5.5 (4). This large variation between both of the pHs allowed for the solution to be titrated in order for neutrality to be reached first so that an acid could be yield. At this point, the mixture was now infused with bromocresol green and its appearance displayed to be green, which signifies that an endpoint had been reached; however, if the mixtures appearances were to be yellow then the solution was titrated beyond its endpoint resulting in production of carbon dioxide (2). In order to correct this, the solution was then needed to be boiled once again until all of the carbon dioxide was removed so that solutions appearance could return to its original color of green (4). Once all of the carbon dioxide had been removed from the solution the next step consisted of performing additional titrations until the correct the endpoint was achieved.
3 Procedure: Part 1 (Preparation of Impure Na 2 CO 3 ) Materials: Minimum 12 g of dried soda ash (unknown), phenolphthalein indicator, bromocresol green indicator, minimum 1 L of standardized HCl (0.12 M), 200 mL of 6 M HCl Solution, and pH paper. Qualitative Observation: In this analysis, there were quite a few qualitative observations that needed to be documented. The first observation documented for this analysis was the appearance of the mixture once the addition of sodium carbonate and phenolphthalein were mixed together with water that resulted in a bright pink solution. Next, HCl was added to the solution in order for the solution mixture to become neutral and colorless. Now that the addition of HCl had taken place not only did this allow for the solutions appearance to change from bright pink to clear, but it also resulted in a reached endpoint. Another observation that was witnessed in this analysis Gather a clean and dry

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