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ChemLab113-0040 - proceed with at least one further...

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Unformatted text preview: proceed with at least one further titration in the latter case, as in Experiment 2. 1f the results are still not acceptable, see the instructor for further directions. (Note that you will lose points for each titration after the third, which is different from Experiment 2 where you were allowed four free titrations). At the end of the period make sure to leave your buret filled with distilled water. See that the magnetic stirrer is turned ofi‘ and that the pH detector is immersed in the beaker of red solution. When you complete the experiment, retain any remaining soda ash and retain the acid solution in the brown bottle. What the Computer Does Your first use of the computer in this experiment is to have it specifir the ideal range of soda ash sample masses. To see how that is done we will consider the sample data for a rough titration contained in the following table. Soda Ash Rough Titration Mass of soda ash 0.4031 g Initial buret reading 0.12 mL Final buret reading 23.58 mi. We see from the data that 23.46 mL of acid was used. That volume is considerably smaller than ideal; the volume should be as large as possible in order to minirmze the importance of the uncertainty in locating the equivalence point, but still safely below the 50 mL capacity of the buret. The ideal range is 30-40 mL. There is a simple—proportion relation between the mass of soda ash used and the volume of HCl solution required to titrate it. The computer uses that relation to specify the minimum and maximum masses to use, as shown in- the following calculations. . . _ 30.00mL _ Mmlmum mass — 0.4031 g (23.46 ) 0.5155 g , _ 40.00 mL _ Maxrmum mass — 0.4031 g (23.46 ) 0.6873 g When you proceed to the precise titrations the computer collects the kind of data shown in the following table. (It takes the HCl molarity from your results for Experiment 2.) 56 ...
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