Acid-Base Titration Lab

Acid-Base Titration Lab - Christina Wong AP Chemistry, 4th...

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Christina Wong AP Chemistry, 4 th Hour 3/10/2010 Acid-Base Titrations Lab I. Purpose Part 1 Our purpose in this lab was to standardize a solution of NaOH using KHP, so that it could be used as a titrant in a neutralization reaction. Part 2 Our purpose in this lab was to identify an unknown diprotic acid by finding its molecular weight. II. Procedure Part 1 We began by obtaining a sample of potassium hydrogen phthalate (KHP), and using an analytical balance, accurately weighed a small sample of it in a previously tared weighing dish. We recorded its precise mass, and then transferred it into an Erlenmeyer flask. Using water from a wash bottle, we rinsed the entire remaining solid from the weighing dish, and then added about 40 mL of distilled water to the flask, swirling until all the KHP was dissolved. We then obtained 75 mL of sodium hydroxide solution, cleaned a 50-mL buret, and rinsed it with three small portions of the NaOH solution. We filled the buret to above its zero mark with the NaOH solution. Opening the buret to allow air bubbles to escape from the tip, we closed it and measured the precise volume of the solution inside. Positioning the buret over the Erlenmeyer flask, we added three drops of phenolphthalein solution to the KHP in the flask. We then started the titration by adding 1.0 mL of NaOH to the Erlenmeyer flask, and swirling the flask to mix the contents. We did this until 15 mL of the NaOH solution had been added to the flask. We reduced incremental volumes of
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NaOH solution to 0.5 mL, until the pink color that resulted started to persist. We reduced the rate of addition of NaOH solution to drop by drop until the pink color persisted for 15 seconds. We measured the final volume of NaOH, and recorded this as the “final volume”. We repeated the standardization titration twice more. The second time, we weighed a small amount of a sample of unknown acid in a weighing dish using an analytical balance, and recorded its precise mass. Dissolving the unknown acid in 40 mL of distilled water, we titrated it to the phenolphthalein endpoint as we had before. We repeated once more, determining a final equivalent mass of the unknown acid. Part 2 Lastly, we set up a pH meter and electrode. We calibrated the pH meter using a pH 7.0 buffer solution, and rinsed the electrode with distilled water. Using an analytical balance, we weighed a sample of unknown acid that required 20 mL of titrant. We dissolved the acid in approximately 100 mL distilled water in a 250- mL beaker and filled the buret with the standardized NaOH solution. We recorded its initial volume as the “initial buret reading”, and set the beaker containing the unknown acid solution on a magnetic stirrer. With the pH reading stabilized, we
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This note was uploaded on 12/03/2011 for the course CHEM BIO P 101 taught by Professor Kk during the Spring '11 term at Rochester.

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Acid-Base Titration Lab - Christina Wong AP Chemistry, 4th...

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