Kinetics of Crystal Violet Fading

The purpose of this laboratory investigation was to use spectroscopy and graphical analysis to determine the rate law for the color-fading reaction to crystal violet with NaOH.

Materials

On page 55 from Sara's lab NB

Procedure

On page 55 from Sara's lab NB

Data Analysis and Results

The following represents the concentrations vs. time data for a zero, first and second order reaction:

Concentration vs. Time Graph

In this graph, Crystal violet was not a zero order in the reaction with NaOH due to the fact that the relationship was not linear.

Natural Log of Concentration vs. Time Graph

In this graph, crystal violet is a first order in the reaction with NaOH because the relationship was linear/very close to being linear.

1/Concentration vs. Time

In this graph, I saw the relationship between 1/concentration and time was not linear, just like the zero order. After knowing that information, CV+ was a first order.

Calculations

Equation 1 CV+ + OH- CVOH

Equation 2 Rate = k [CV+]n [OH-]m

Equation 3 Rate = k' [CV+]n

Equation 4 k' = k [OH-]m

Equation 5 A = b c

A=abc

A= 0.0725c

Conclusion

The pseudo rate law for the reaction between CV+ and OH- is rate=k [CV+], where CV+ and NaOH are both first order and k = 0.07251M2s. When the data for absorbance time was manipulated and plotted into three different graphs ([CV+] vs. Time, ln[CV+] vs. Time, 1/[CV+] vs. Time), the R2 value for our first order graph (ln[CV+] vs. Time) was 0.0996. Compared to the other R2 values, this value was the closest to one, meaning it the most linear. Because the ln[CV+] vs. Time graph was linear, we were able to conclude the CV+ was first order because the data fits the first order integrated rate law: ln[CV+]= - kt + ln[CV+]0 . Using the best fit line, we were able to find our slope which was also our constant k, the order of the reaction and our rate law.

Error Analysis

What went wrong? What will you correct in order to do better next time?

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