8 measure the mass of an empty 125 ml erlenmeyer

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Unformatted text preview: an estimate. 8 Measure the mass of an empty 125 mL Erlenmeyer flask and record this value in Table A1. Using the 10.0 mL graduated cylinder, transfer 10.0 mL of vinegar into the flask. Weigh the flask and vinegar together and record the mass in Table A1. 9 Add ~10 mL of deionized water (Do not use the graduated cylinder for this now that it is conditioned for vinegar!) and 3 drops of phenolphthalein solution to the flask containing the vinegar. 10 Open the stopcock of the buret and add some titrant (NaOH) to the contents of the flask (HC2H3O2 + water + indicator). Swirl the flask gently to mix the solutions. 11 Continue to add titrant to the flask with swirling. As the addition proceeds, you will see a faint pink color appear and quickly fade. When the color begins to disappear more slowly, slow the addition of titrant to a dropwise rate. Rinse the walls of the flask and the tip of the buret with deionized water from a wash bottle as you approach the endpoint. This ensures that all of the NaOH delivered from the buret ends up in the reaction mixture. The endpoint has been reached when the faint pink color lasts for at least 30 s e conds . Record the final reading on the buret to the nearest 0.01 mL in Table A1. 12 Repeat steps 6 - 11 with a second sample of vinegar. If the results of the two trials differ by more than 0.50 mL, titrate a third sample. You will need to clean one of your Erlenmeyer flasks to perform a third titration. Discard the trial with the darker pink color. For the third titration, try to match the color of the remaining endpoint as well as you can. 13 When finished, drain the remaining NaOH from your buret into your 100 mL beaker. Discard all solutions as directed by your instructor. 14 Rinse all of your glassware with water, dry it and return it to the set- up area where you found it. 15 Before leaving, go to a computer in the laboratory and enter your results in the In- Lab assignment. If all results are scored as correct, log out. If not all results are correct, try to find the error or consult with your lab instructor. When all results are correct, note them and log out of WebAssign. The In- Lab assignment must be completed by the end of the lab period. If additional time is required, please consult with your lab instructor. Copyright © 2011 Advanced Instructional Systems, Inc. and North Carolina State University | Credits www.webassig n.net/ebooks/wsug encheml1/lab_10/manual.html 5/5...
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