Chemistry 14CL FALL 2002 POSTLAB REPORT GUIDELINES FOR THE KINETICS EXPERIMENT This is a GROUP REPORT Note: review the kinetics lecture guide and your 14A or 14B lecture materials on chemical kinetics BEFORE you complete this postlab report. (I) DATA & DATA ANALYSIS (MUST show ALL your work in order to receive any credit) - Write down the names of all the members in the group. Write out the responsibility of each member both for the experiment and for the postlab report. - Calculate the molarity for the diluted bleach solution. (you may assume that the stock bleach solution contains only NaOCl and that the concentration given on the bottle has a unit of w/v%) - Calculate the precise molarity of food-dye solution 1 and food-dye solution 2. - Calculate the initial concentration of the food-dye solution in EACH trial. - Using the Beer's law formula, calculate the molar extinction coefficient, ε, for the food dye. You may assume that the diameter of the culture tube to be 1.00cm. - In tabular form, now set up an EXCEL spreadsheet table for EACH trial. Label the columns as time, absorbance, [dye], ln [dye] and 1/[dye]. Note: [] means the concentration has a unit of mol/L. Note: For trials #1, 2 & 3, set up data table for EACH trial from time = 0 sec to time = 400 sec. For trials #4, 5 & 6, set up data table for EACH trial from time = 250 sec to time = 900 sec. Using EXCEL, now fill in the spreadsheet that you set up for EACH trial with the appropriate values. - Provides a legend for each table that gives the experimental condition (temperature, volumes of each reagent etc.) - Using trial #1 & #2, determine the molecularity (or order) of the bleach in the rate expression base on the instantaneous reaction rates. - Using trial #1 & #3, determine the molecularity (or order) of the bleach in the rate expression base on the instantaneous reaction rates. - Compare the two calculated values for the molecularity of the bleach. What can you conclude? Explain. (Hint: calculate the instantaneous reaction rate for the plot of [dye] vs. time for trial #1,2 & 3 at around 30 - 50 seconds or so and use that to find the molecularity of the bleach solution in the rate expression. As an approximation, you may use the INITIAL concentrations of the bleach from trial #1, #2 & #3 when calculating the molecularity of the bleach. In addition to the restriction to the time requirement, the point that you pick on the graph (trial #1, 2 & 3) for calculating the instantaneous reaction rate should also be similar in the concentration of food-dye.)Chemistry 14CL FALL 2002 POSTLAB REPORT GUIDELINES FOR THE KINETICS EXPERIMENT This is a GROUP REPORT (I) DATA AND DATA ANALYSIS (CONTINUE) - Using trial #4 & #5, determine the molecularity (or order) of the food-dye in the rate expression base on the instantaneous reaction rates. - Using trial #4 & #6, determine the molecularity (or order) of the food-dye in the rate expression base on the instantaneous reaction rates. - Compare the two calculated values for the molecularity of the food-dye. What can you conclude? Explain. (Hint: For trial 4,5 & 6, calculate the instantaneous reaction rate around 300 - 350 seconds or so and use that to find the molecularity of the dye in the reaction. In addition to the restriction to the time requirement, the point that you pick on the graph (trial #4, 5 & 6) for calculating the instantaneous reaction rate should also be similar in the concentration of food-dye. In that case, you may assume that the concentrations of the bleach are the same at the points that you pick for calculating the instantaneous reaction rate.) (II) Graphs (Use EXCEL or any other spreadsheet software for this part of the report) - For EACH trial, plot the following three sets of graphs: [dye] vs. time; (b) ln [dye] vs. time and (c) 1/[dye] vs. time - From the graphs, comment on the order (or molecularity) of the food-dye in the rate expression. Compare this result with the order of the food-dye that you obatined from the data analysis part. What can you conclude? (i.e. does the graphs confirm the order of the food-dye in the experimental rate law that you obtained earlier in the data analysis section? Why or why not?) - For EACH trial, graphically determine the rate constant (k). (Hint: make sure you use the correct graph when calculating the rate constant!!). NOTE: It turns out that the concentration of the bleach is much higher than that of the dye in ALL trials. This implies that the integrated rate law is that for a PSEUDO-FIRST ORDER. Because it is a PSEUDO FIRST ORDER kinetics, the integrated rate law gives a straight line for ln[dye] vs. time and the SLOPE of the line is equal to -k * [Bleach] (at t=0). In other words, the “real” rate constant, k, = -slope / [Bleach] at t=0Chemistry 14CL FALL 2002 POSTLAB REPORT GUIDELINES FOR THE KINETICS EXPERIMENT This is a GROUP REPORT (III) Conclusion - Summarize results and write down the experimentally determined rate law for the reaction of food-dye with bleach. - Compare the rate constant for EACH trial. What can you conclude? - If the overall reaction is second order, what theoretical method (or model) will you use to prove that this is true?
View Full Document
Unlocking...