Passage IV Experiment 2 In the first trial, 1.00 mL of a solution of DNPA in met
ID: 1005273 • Letter: P
Question
Passage IV Experiment 2 In the first trial, 1.00 mL of a solution of DNPA in methanol was added to 500 mL of a pH 5.0 buffer solu tion (an aqueous solution that maintains a constant pH). The resulting reaction solution was then continuously stirred at 27°C. Every 15 min, a 0.010 mL sample of the reaction solution was removed and then quickly injected and DNP. into the HPLC. The peak areas for DNPA and DNP were In nature, many pollutants hydrolyze (react with H-0 to decompose). The chemical DNPA hydrolyzes to form the chemical DNP as follows: DPA + H2O DNP + acetic acid Chemists did 2 experiments to study DNPA and DNP. recorded. A second trial was then performed using the same pro- cedure except that a pH 8.5 buffer solution was used (see Experiment I A solution made by dissolving certain amounts of Table 2). DNPA and DNP in methanol was injected into an apparatus called an HPLC. In the HPLC, the solution was carried by a flow of solvent through a column packed with adsorbent. Each component of the solution had a different retention time (the amount of time the component remained in the column). As a component exited the column, it passed through a detector, which produced a peak on a graph. The peak area (the area under the peak) was related to the con- centration of the component in the solution, but the reten- tion time was not (see Figure 1). Table 2 Peak area Time pH (min) DNPA DNP 5.0 30 134 75 119 0 146 30 93 DNPA peak 45 128 12 60 123 15 DNP peak 45 58 36 60 38 59 75 32173 146 36 93 36 58 59 38 73 shading indicates the peak Figure and tables adapted from Jörg Klausen, Markus A. Meier, and René P. Schwarzenbach, "Assessing the Fate of Organic Con- taminants in Aquatic Environments: Mechanism and Kinetics of Hydrolysis of a Carboxylic Ester..1997 by Division of Chemical Education, Inc., American Chemical Society. retention time (min) Figure 1 The process was repeated for different solutions of DNPA and DNP (see Table 1). 19. In the trial in Experiment 2 at pH-8.5. as time increased from 0 min to 75 min, the DNPA concentration: Table 1 increased only B. decreased only C. increased, then remained constant. D. decreased, then remained constant. ConcentrationPeak area Solution DNPA DNP DNPA DNP 0 1096 20. Experiment 1 1 established the relationship between: 30 1s 146 15 60 45 | 15 109 | 30 60 15 13 91 30 30 73 61 F. concentration and peak area for DNPA and for DNP G. temperature and peak area for DNPA and for DNP H. pH and peak area. J. pH and retention time. 15 30 109 0 60 36 61Explanation / Answer
19. In the trial in Experiment 2 at pH = 5 DNPA concentration
B. Decreased only
20. Experiment 1 established
F. concentration and peak area for DNPA and DNP (as we can see in table 1 - concentration decreases as peak area decreases)
21. Graph shows
D. At pH = 8.5 for DNP
22.
H . DNP, because DNP had the shorter retention time. (As we can see in figure 1 – 3.6 min)
23.
A. using an acidic buffer solution, the second trial was carried out using a basic buffer solution. (First trial was carried out at pH 5. Which is acidic. For second trial pH 8.5 was used which is basic pH).
24.
J. 45 mg/L and 60 mg/L
(If we correlate both experiments, from table 1 and table 2, we can easily deduce the concentration.
Table 1,DNPA solution 1 and 2 has peak area 109-146, with concentration of 45 – 60 mg/L
Table 2, pH 5, 30 min, peak area is 134 mm2. Which is between 109-146.)