and 11.9). Determine the line of best fit determine which plot is most linear an
ID: 945869 • Letter: A
Question
and 11.9). Determine the line of best fit determine which plot is most linear and hence the correct order of the reaction in B blue. Calculate k' for this trial. equations 17.7, 17.8 through each set of data. Using the R-squared val Using the relationship chosen for the first trial, plot the data for the remaining trials an and determine the value of k' for each of them. Finally, use the k values computed for each trial to determine the order of the reaction in hydroxide (with uncertainty) by plotting the relationship in equation (17.11). Calculate true rate constant with uncertainty ide (with uncertainty) by plotting the relationship in equation (17.11). Calculate the l as the answers to Make sure that your full set of annotated calculations and figures, as well as the the Questions for Thought, are included as your Supporting Information. answer Questions for Thought 1. Write the full differential rate law for the decomposition reaction of Bromophenol blue with hydroxide. What is the overall order of the reaction? 2. Why is k'referred to as a "pseudo" rate constant? 3. Why was NaNOs used to dilute the samples (and as a blank) instead of deionized water 4, what is the half-life of Bromophenol blue for the trial used in #1?Explanation / Answer
1. Bromophenol blue undergoes reaction at higher pH which is slow and pH dependent.
The reaction of Species II Bromophenol blue with hydroxide ion is first order with respect to each reactant and second order overall.
The rate law for this reaction is:
Rate = k2 [II] [OH1-] where [II] is the molar concentration ofSpecies II and k2 is the second order rate constant.
Note: In the write-up the structures of I, II, and III (kinetics product) are given.
2. When we run this above reaction with 1.0 and 0.50 M NaOH then both concentrations are very much larger than the indicator and result in pseudo first order rates forthe indicator. i.e.
k1 = k2 [OH1-] and Rate = k1 [II]
where k1 is the pseudo first order rate constant. The integrated rate equation is:
log [II] = -k1 t / 2.303 + log [II]o
where t is the time, [II]o is the concentration of Species II at t=0
3. A blank solution is used to calibrate the spectrophotometer is that is mostly done with NaNO3 instead of deionizd water. The use of NaNO3 is done to remove the trace amount of impurities to make results more accurate and to subtract background in that absorbance region. The Fe+3 & NO3- ions may absorb slightly in the range that the FeSCN+2 ions do, whereas, the deionized water wouldn't. So to correct for that absorbance we need to use a blank that contains these ions.The major issue with using DI water as a blank is that DI water does not take into account the trace impurities that might be present in the reagents you use to prepare your samples to be analyzed by spectrophotometry.
4.Using equation
log [II] = -k1 t / 2.303 + log [II]o
log[2] = -k1 * t1/2 / 2.303 + log[4]
- 0.3 = -k1 * t1/2 / 2.303
k1 * t1/2 / 2.303 = 0.3
k1 * t1/2 = 0.57575
t1/2 = 0.57575 / k1
k1 = 0.0728 +/- 0.0005
t1/2 = 0.57575 / 0.0733 = 7.854 sec
or
t1/2 = 0.57575 / 0.0723 = 7.963 sec
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