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I. Preparation of Required Solutions A. p-Nitrophenyl acetate stock solution (1.00 X 10-4 M NPA in 3.0% (v/v) methanol/water) (NOTE: The NPA is not very soluble in water; therefore, methanol is used to dissolve the NPA with subsequent dilution to the appropriate concentration with water.) 1. Measure 3. 2. Dilute Add flask 30.0 (or 250-mL out mL 18.1 methanol; Erlenmeyer mg of mix NPA flask). (181.1 g mol-1--record the mass; place into a 100-mL volumetric 4. Take water; 1.0 to mL 100.0 of mL this total solution volume and to dissolve. with place deionized water; mix well. mix well. in separate container; to this 1.0 mL add 9.0 mL deionized B. p-Nitrophenol stock solution to (NOTE: the NPA The methanol is used in the NP solution analogous solution.) simply to make the solvent conditions 5. Measure flask (or 250-mL out 13.9 Erlenmeyer mg of NP (139.11 g mol-¹-record the mass; place into a 100-mL volumetric 6. Add 30.0 mL methanol; mix to flask). dissolve. 7. 8. Take Dilute to 100.0 mL total volume with deionized 5.0 mL of this solution and place in separate water; container; mix well. add 45.0 mL deionized water; mix well. C. Aqueous methanol solution 9. In a 100-mL graduated cylinder, add 3.0 mL methanol; dilute to 100.0 mL with deionized water; mix well. D. NaOH solution (3.16 x 10-4M) 10. Dilute 9.48 mL of standardized 0.0010 M NaOH solution to 30 mL using deionized water; mix well. E. KCI solution (n3 M) 11. Measure out 6.7 g of KCl and place into a 50-mL Erlenmeyer flask. 12. Add 30 mL of deionized water; mix well. II. Measurement of Molar Extinction Coefficient of p-Nitrophenol at Two [Hydroxide] 13. Prepare a series of four NP samples at different NP concentrations for each hydroxide concentration: 0.00,M [Hydroxide] = 0.0010 -4 M 14. Label four test tubes (1, 2, 3, and 4). 15. In each test tube, make the following mixtures: Tube 1: 4.0 mL 3 M KCl 4.0 mL NP stock 4.0 mL 0.0010 M NaOH Tube 2: 4.0 mL 3 M KCl 3.0 mL NP stock 4.0 mL 0.0010 M NaOH 0.001 m 1.0 mL deionized water Tube 3: 4.0 mL 3 M KCl 2.0 mL NP stock 4.0 mL 0.0010 M NaOH 2.0 mL deionized water Tube 4: 4.0 mL 3 M KCl 1.0 mL NP stock 4.0 mL 0.0010 M NaOH 3.0 mL deionized water Experiment/Subjeçt Rinetics: Th 0f 0-N.t-2 [Hydroxide] = 3.16 X 10-4 M 17. 16. Prepare Repeat steps two blank 14 to 15 using tubes labeled 5 3.0 mL of 3 M KCl solutions (one at each [hydroxide]) to 8, and 3.16 by mixing X 10-4 the M NaOH. following solutions together: 3.0 3.16 mL X 0.001g 10-4 M M) NaOH ([hydroxide] = 0.0010 M) or 3.16 X 10-4 M NaOH ([hydroxide] = 3.0 mL aqueous methanol solution 18. Zero [hydroxide] the absorbance = 0.0010 measuring M. device of choice using the blank solution (step 17) for 19. each Measure the absorbance at 405 nm for samples 1 through 4; record the absorbance. [NOTE: For piece measurement, of be sure the cuvette is clean, the the cuvette wiped with a outside of is clean stop 20. Repeat steps 18 and 19 to collect absorbance measurements at [hydroxide] = 3.16 X 10-4 M. lens paper, and avoid bubbles (which will interfere with the measurement).] III. Determine Reaction Order for p-Nitrophenyl Acetate at Two Different [Hydroxide] [Hydroxide] = 0.001 M 21. Place the [hydroxide] = 0.0010 M blank from step 17 into a cuvette and zero the absorbance measuring instrument at 405 nm; then clean and dry the cuvette. 22. To the empty cuvette, use a pipetter or Pasteur pipette to add the following solutions directly into cuvette and mix well: 1.0 mL 3 M KCl 1.0 mL 0.0010 M NaOH As you add each additional solution, add directly into the previous liquid in the cuvette to get good mixing (avoiding bubbles, obviously). 23. Clean the outside of the cuvette with a piece of lens paper, and insert the cuvette into the absorbance measuring device. 24. You will next be adding 1.0 mL of the NPA stock solution. (NOTE: This reaction will begin as soon as it is mixed, and is finished in a short period of time! Add the npa stock directly to the cuvette into the solution to get good mixing, and begin collecting absorbance data immediately.) 25. Record the absorbance at 405 nm every 10 sec for a period of 360 sec. [Hydroxide] = 3.16 X 10-4 M 26. Repeat steps 21 to 25 making the following changes: Use [hydroxide] = 3.16 X 10-4 M blank to zero the absorbance. The sample will contain 1.0 mL of 3.16 X 10-4 M NaOH. Data Collection I. Preparation of Required Solutions Mass of NPA: 2. Mass of NP: 6.704g 0.0159 II. Measurement of Molar Extinction Coefficient of p-Nitrophenol at Two [Hydroxide] 3. Absorbance measurements (405 nm) for NP solutions: Experiment/Subjeçt Rinetics The Hy arilysis Name of Acetate P-Nitrpheng Date 6-20-19 Marie Celis Lab Partner Locker/ arc Jacqueline Luna Dest' NT 15 17 Tube # 0.0010 / M NaOH 3.16 X 10-4 M NaOH - MM t 1 dx 0.333mm A405 A t 2 3 0.025 mm 0 400 DHO17mm 562 O.csn 8 456 314 1200 + 4 += 5 8 6 2797 A = ed C 7 B 724 a= Et l 8 s 730 III. E = Hop [Hydroxide] Determine = Reaction Order for p-Nitrophenyl 074% Acetate at Two Different l D : 0.0010 M [Hydroxide] or mm' 4. Absorbance Time (sec) (405 , nm) as a function of time for NPA hydrolysis 1cc ) A405 reaction: - /mm.c 10 Time (sec) 18 20 190 A405 30 200 40 210 50 220 60 230 70 240 80 250 90 260 100 270 110 280 120 290 130 300 140 310 150 320 160 330 170 340 180 350 360 237 8. Tube Calculate 1: the [NP] in each test tube: of I-Nitrophenol at Two [Hydroxide] Tube 2: Tube 3: Tube 4: Tube 5: Tube 6: Tube 7: Tube 8: 9. Plot A405 VS. [NP] for both hydroxide concentrations: 10. Using Excel, a graphing calculator, or the least-squares method, fit your data above to a straight line of the form: A405 = (E : X ) X [NP] + (y - intercept) [OH-] = 0.0010 M [OH-] = 3.16 X 10-4 M (a) Slope of your line (including units): (b) Y-intercept of your line (including units): n. Determine the molar extinction coefficient of NP at both [hydroxide]: [OH~] = 0.0010 M €405 = [OH~] = 3.16 X 10-4 M €405 =

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