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Richard BryantAP Chemistry, 4thHour3/14/2009Acid-Base Titrations LabI.PurposePart 1Our 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 2Our purpose in this lab was to identify an unknown diprotic acid by finding its molecular weight.II.ProcedurePart 1We 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 all of the 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 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.