B. Molar Concentration of an Acid Solution Acid type, HA or H,A: HCL Unknown No. Balanced equation for neutralization of acid with NaOH. Bale NaOH + HCl + HCI- NaCl + + H2O HCl unvenown A Sample ! Sample 2 SmL Sample 3 25.0 5ML 25.0 25.0 1. Volume of acid solution (mL) 6.6mL 10.0mL OmL 3.7mL 2. Buret reading of NaOH, initial (mL) 3. Buret reading of NaOH, final (mL) 4. Volume of NaOH dispensed (mL) final intiala 5. Molar concentration of NaOH (mol/L), Part A 0,619 6. Moles of NaOH dispensed (mol) 7. Molar concentration of acid solution (mol/L) 8. Average molar concentration of acid solution (mol/L) Data Analysis, B TOT 9. Standard deviation of molar concentration Data Analysis, 10. Relative standard deviation of molar concentration (%RSD) Data Analysis, D Laboratory Questions Circle the questions that have been assigned. 1. Part A.1. Pure potassium hydrogen phthalate is used for the standardization of the sodium hydroxide solution. Suppose that the potassium hydrogen phthalate is not completely dry. Will the reported molar concentration of the sodium hydroxide solution be too high, too low, or unaffected because of the moistness of the potassium hydrogen phthalate? Explain. 2. Part A.2. The student forgot to prepare any boiled, deionized water for the preparation of the NaOH solution and then carelessness? Explain. forgot to cap the bottle. Will the concentration of the NaOH solution be greater than, less than, or unaffected by this be reported as too high or too low? Explain. 3. Part A.6. A drop of the NaOH titrant adheres to the side of the buret (because of a dirty buret) between the initial and final readings for the titration. As a result of the "clean glass" error, will the molar concentration of the NaOH solution 4. Part A. The mass of KHC,H,O4 is measured to the nearest milligram; however, the volume of water in which it is dis- water added to the KHC,H,O, has no effect on the data, whereas water added to the NaOH solution solved is never of concern-water is even added to the wall of the Erlenmeyer flask during the titration. Explain why affect the data. may drastically reported as too high, too low, or unaffected? Explain. 5. Part B.2. The wall of the Erlenmeyer flask is occasionally rinsed with water from the wash bottle (see Part A.6) during the analysis of the acid solution. Will this technique result in the molar concentration of the acid solution being 6. Parts A.6 and B.2. For the standardization of the NaOH solution in Part A.6, the endpoint was consistently reproduced to a faint pink color. However, the endpoint for the titration of the acid solution in Part B.2 was consistently repro- duced to a dark pink color. Will the reported molar concentration of the acid solution be too high, too low, or unaf- fected by the differences in the colors of the endpoints. Explain. 142 A Volumetric Analysis Experiment 9 Report Sheet A Volumetric Analysis Desk No. Date Lab Sec. Name Maintain at least three significant figures when recording data and performing calculations. Notebook A. Standardization of a Sodium Hydroxide Solution Calculate the approximate mass of NaOH required to prepare 500 mL of a 0.15 M NaOH solution (Part A.2). First find molar mass of NaOH Na 23 O 16 1. Н H I 40 = molar mass Calculate the approximate mass of KHC,H,O, for the standardization of the NaOH solution (Part A.3). To prepare 0.15 M phthalate Molarity = moles Notebook Trial 1 Trial 3 Trial 2 1.537 1.537 5379 1.537 7g 1. Tared mass of KHC2H404 (8) 204.23 g/mol 2. Molar mass of KHC2H404 -0.0075 0.0075 0.0075 3. Moles of KHC2H404 (mol) Titration apparatus approval 4. Buret reading of NaOH, initial (mL) 5. Buret reading of NaOH, final (mL) 0-8.9mL 8.9-17.8mL 17.8-27.9 mL 8,9mL 17.8mL 27,9m2 8.9mL 17,8mL 27.9mL . . 169 . 169 149. 6. Volume of NaOH dispensed (mL) 7. Molar concentration of NaOH (mol/L) Data Analysis, B molar concentration of NaOH (mol/L) 8. Average Data Analysis, C 9. Standard deviation of molar concentration 10. Relative standard deviation of molar concentration (%RSD) Data Analysis, B Experiment 9 141
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