Rate Law Determination of a Crystal Violet Reaction
Objective: To determine the reaction order with respect to crystal violet and determine the rate constant and half life for the reaction: [CV+ + OH– Þ CVOH].
Procedure:
(1) Calibrate the Colorimeter with distilled water.
(2) Prepare a solution with 10ml each of the provided CV and OH.
(3) Let solution stand for 3 minutes before beginning (4).
(4) Place solution in Colorimeter and record data point with software.
(5) Remove solution for one minute.
(6) Repeat steps (4-5) twenty times, [20 minutes].
(7) Calculate reaction order, rate constant, and print data/graph.
Analysis:
In this experiment, we observed rate properties for the reaction:
[CV+ + OH– Þ CVOH], using a Colorimeter tool and computer software to track the absorbance of a 1/1 solution of 0.02M NaOH and 2×105M Crystal Violet. The reaction’s color changed over time, as more CV was being consumed, and allowed us to chart this rate in graphical form. Studying the graphs, we determined that the rate was in first order with respect to Crystal Violet: Rate = k[CV]1.
Moreover, using Beer’s Law, we substituted our data into the standard first order equation: ln(€bct) = -k(t) + ln(€bco), finding that the rate constant is approximately 0.0909. This seems a reasonable answer, but there could be error in our data; the Colorimeter tracks the slightest changes, and as such, when a fingerprint or similar is placed on the solution container, the data could erroneous. Similarly, contamination of the solution could cause similar results.
Results:
| [CV–] after mixing | 0.00001M |
| [OH–] after mixing | 0.010M |
| Reaction order with respect to CV– | 1st order |
| Rate constant k | 0.0909 |
| Rate law expression (omit OH–) | Rate = k [CV] |
| Half-life of the reaction | 7.91s |
