acid-base equilibria

Acid-base equilibria - Chemistry 154.002 Experiment 6 Acid-Base Equilibria Lauren Best Partner Glenn Cormack TA Lek 1 Objective The purpose of this

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Chemistry 154.002 Experiment 6 Acid-Base Equilibria Lauren Best Partner: Glenn Cormack 3/24/08 TA: Lek 1. Objective The purpose of this experiment is to firstly, determine the acid-dissociation constant of an unknown weak acid by performing a computer aided titration; secondly, to determine the concentration of this weak acid in the unknown solution; and thirdly, to calculate the molar mass of the unknown acid. 2. Procedure A) An aqueous solution of NaOH is needed for this experiment. To make this, place about 3 or 4 pellets of NaOH to about 100 mL of water. Stir well with a stirring rod and cover with a watch glass. Be certain to label the beaker. B) The pH probe needs to calibrated. Obtain 15 mL of pH 4 and pH 10. Rinse the pH probe with deionized water. Follow the calibration steps on pg. 63 of the lab manual. C) The standardization of the NaOH solution needs to be determined. Fill buret with NaOH solution. Use a pipet to dispense exactly 10 mL of KHP into a 50 mL beaker. Rinse, and place pH probe in KHP, making sure to swirl the solution. Start collecting data, making sure to press the “keep” button when the pH stabilizes. Take the pH probe out of the KHP, add about 0.5 mL of NaOH, and return the probe to the solution, making sure to swirl the solution. Repeat until the pH rises sharply. D) Perform step C for the acid concentration. Make sure to do at least 2 titrations for the unknown. 3. Sample Calculations A) given: [KHP] = 1.00x10 -1 M V(KHP)= 10.00 mL V(OH eqv )= 11.98 mL then, [OH] = 8.35x10 -2 M B) given: [OH] = 7.89x10 -5 M
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V(OH eqv )= 10.87 mL V(HA)= 1.00x10 1 mL then, [HA]= 8.58x10 -5 M C) Given: pH 2 = 4.1770 pH 1 = 4.0375 V 1 = 0.0000 mL V 2 = 0.5100 mL Then, slope= 0.2735 D) Given: pH= 2.90 [HA]= 1.04x10 -1 M Then, K a = 1.54x10 -5 E) Molar Mass= 19.002/ [HA) 0 M Molar Mass= 19.002/(.1003) M
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This note was uploaded on 04/17/2008 for the course CHEM 154 taught by Professor Richter during the Spring '08 term at The University of Akron.

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Acid-base equilibria - Chemistry 154.002 Experiment 6 Acid-Base Equilibria Lauren Best Partner Glenn Cormack TA Lek 1 Objective The purpose of this

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