Acid-Base Lab - Chris Stanton Lab Report Acid/Base...

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Chris Stanton 10/19/06 Lab Report: Acid/Base Titration I. Introduction During this experiment, the goal was to eventually determine the molar mass and pKa of an unknown acid. A series of preliminary steps and data collection is needed before those calculations can be made. First, the base NaOH (approximately 0.1M) is titration with a known acid, KHP. After titration, the exact molarity of the NaOH solution can be determined by using the starting amount of KHP in your sample, the molecular mass of KHP, and the amount of NaOH used. After this, you are ready to begin testing your unknown acid. A preliminary titration is done first to see about how many milliliters of NaOH are needed to titrate approximately 500 mg of your unknown acid. A calculation is then done to predict how much of your unknown acid you would need to use between 30 and 40 mL of NaOH. A series of calculations are then done to produce a table that can guide you through the precise titrations in order to collect accurate data. The precise titration is done three times for accuracy, from which the molecular mass of your acid and the pKa can be determined. II. Experimental Data 1. Before the beginning of the actual laboratory experiment, the KHP and NaOH are obtained and the KHP is dried out for two hours. The KHP is then kept in a desicooler until the following week when the titration segment begins. 2. 800 – 850 mg of KHP is weighed out three times and each sample is placed in three 250 mL flasks. The KHP is dissolved in 50 mL of water and then 4 drops of Phenolphthalein is added to each flask. 3. Each flask is titrated to within one drop of the endpoint and when the endpoint occurs, the amount of NaOH is noted, which can be used along with the molecular mass of KHP to determine the actual molarity of NaOH. This is shown below and after the three molarities are calculated, an average is taken to determine the molarity of NaOH that will be used for the remainder of the experiment. Molecular Mass of KHP = 204.22 g First Sample of KHP Weight = 840 mg Amt. of NaOH used = 47.18 mL M of NaOH = (840 mg KHP) x (1g/1000mg) x (1mol KHP/204.22g) x (1/47.18mL) x (1000mL/1L) = 0.0872 M NaOH Second Sample of KHP Weight = 848 mg Amt. of NaOH used = 47.95 mL M of NaOH = (848mg KHP) x (1g/1000mg) x (1mol KHP/204.22g) x (1/47.95mL) x (1000mL/1L) = 0.0866 M NaOH
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Third Sample of KHP Weight = 850 mg Amt. of NaOH used = 48.00 mL M of NaOH = (850mg KHP) x (1g/1000mg) x (1mol KHP/204.22g) x (1/48.00mL) x
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