Chemistry 14BLWinter 2003Pre-Lab Work (individual)IntroductionIn-Lab WorkPost-Lab Notebook Report (Group)Chemistry 14BL Winter 2003 Report Guidelines for “Kinetics of FD&C Red #3” The following guidelines for the report are reproduced directly from the assignment that was prepared for this quarter’s class. The Prelab Study Questions are posted on VOH and reproduced here. They are due along with the prelab report introduction at the beginning of your lab period during the week of March 4- 7. PRE-LAB WORK (INDIVIDUAL) Study Questions: 1. Calculate the molarity of a 6.15% (w/v%) sodium hypochlorite (NaOCl) solution. 1. Calculate the molarity of a solution of Erythrocin B (MW 879.9 g/mol) if a 0.5028-g sample is diluted to 100 mL in a volumetric flask and then two serial dilutions are carried out in which 5-mL aliquots are diluted to 100 mL using volumetric equipment. 2. The half-life of a substance that is being consumed by a first-order rate reaction is the time required for the concentration to fall to one half of the initial value. Show that for At=Ao2, the equation lnAoAt= k(t − to) becomes t12=0.693k where Ao is the amount at time 0, At is the amount at time t, and t1/2 is the time required for the concentration to fall to one half the initial value. 3. In a few brief sentences, explain a) why it is necessary to mix the solution very rapidly when the bleach is added. b) the purpose of the blank solution. c) how the shapes of the plots [dye] vs time, ln[dye] vs time, and 1/[dye] vs time are used to determine the order of the reaction. Introduction In preparing for lab, set up your notebook with the following information: • The title of the experiment • A reference identifying the procedure handout • A short introduction summarizing the goals of the experiment and the techniques that you will use in the experiment • A brief flow chart summary of the key procedures of the experiment • MSDS information for sodium hypochlorite solutions and erythrocin B sodium • A table to record the preliminary information on dye weight, bleach concentration and initial solution absorbances.• Two data tables to record the measured absorbances and times for the various rate runs. Leave space for a heading that will identify the trial number and the experimental conditions for the trial. IN-LAB WORK Data: (Individual) • Record your partner’s name and the agreed upon allocation of responsibility for the experiment and the report. Indicate in whose notebooks the various data trials will be recorded. All notebooks need to have at least two trials of original data. • Record the weight of food coloring used to prepare Solution 1. • Record the concentration of the bleach solution. • Record the absorbance of Solution 3 (From this point forward, the data is acquired and shared as a group) In tabular format record the time and absorbance readings for each of the six rate trials. Be sure the headings for the tables reflect the experimental conditions for the trial. POST-LAB NOTEBOOK REPORT (GROUP) Calculations: • Calculate the molar concentrations of the three dye solutions. The molecular weight of FD&C Red #3 is 879.9 g/mol. • Using Beers Law, A = εbc, determine the molar extinction coefficient for FD&C Red #3. Use the concentration and absorbance of Solution 3 and assume the diameter of the culture tube (the path length) is 1 cm. • Calculate the initial concentration of dye in each trial at time = 0. • Set up a spreadsheet table for each trial. Label the columns as time, Absorbance, [dye], ln [dye], 1/[dye]. Note: [ ] means concentration in mol/L. • Calculate the data for each cell. Note: Use the measured absorbance of the solution during the trial, the calculated extinction coefficient for the dye, and a path length of 1 cm to determine the [dye] during the rate runs. Graphs: Prepare three graphs for each trial: • [dye] vs. time • ln[dye] vs. time • 1/[dye] vs time. Be sure to title your graphs, and label the axes including units. Analysis: 4. From a visual inspection of these plots, select the linear relationships to establish a, the order of the reaction with respect to the dye. 5. Using the plots that give linear relationships, determine the rate constant for each trial. 6. By comparing the slopes of the lines for trials 1, 5, and 6, determine b, the order of the reaction with respect to hypochlorite.Conclusions: Summarize your results and the justifications for using the graphs you chose to determine the order of the reaction. Kinetics studies can disprove a proposed mechanism but can never prove a mechanism. Explain whether the results that you have obtained are consistent with the mechanism proposed at the beginning of this
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