This document is a procedure for determining the order of the reaction between Fe3+ ions and Iodide ions. This document outlines the steps needed to be taken for the set up of the Labquest and the Colorimeter. It also outlines the procedure for the dilution of solutions as needed in the experiment. Data sheet needed for collection of information is also included along with steps for calculation. Order of a Reaction Using Labquest and Colorimeter Teachers Guide By Stan Vincent,
Order of a reaction Using Lab-quest and Colorimeter. The chemical reaction 2Fe(NO 3 ) 3 + 2KI 2Fe(NO 3 ) 2 + 2KNO 3 + I 2 2Fe 3+ (aq) + 2I - (aq) 2Fe 2+ (aq) + I 2 Setting up the equipment s Turn on the lab-quest and connect the colorimeter should be on at least 5 minutes before you start data collection. Lab quest set up. o > Sensors o > Data Collection o > Time Based o > Rate = 1 o > Interval = 1 o > Length 200 s o > OK Colorimeter o Select the wavelength 470 / 575 nm using < or > o Prepare a blank, fill the cuvette 3/4 th with distilled water o Place it in the colorimeter, the clear side of the cuvette should face the white line o Press calibrate. It is a one button calibration. o When the red light stops blinking and the absorbance on the Labquest is 000 the instrument is calibrated. Reagents provided / required Fe 3+ 0.02 M in a 100 ml Volumetric flask 0.02 M om a 100 ml Volumetric Flask Distilled water in a wash bottle Mix the volumes needed according to the table provided (at least 3 trials; 1,2 &3) Solutions to prepare Trial FeCl 3 (ml) KI (ml) H 2 O (ml) 1 20.0 20.0 0.0 2 20.0 10.0 10.0 3 10.0 20.0 10.0 4 15.0 10.0 15.0 5 10.0 15.0 15.0 NOTE: Do not mix the two solutions until you are ready to record the readings.
DATA TABLE This table now gives you values which can be used to solve for the order of the reaction using initial rate method. Trial [Fe 3+ ] [I - ] Initial rate (s 1 ) C f = C i V i V f C f = C i V i V f 1 0.01M 0.01M Value of m from Labquest 2 0.01M 0.005M 3 0.005M 0.01M 4 0.0075 0.005 5 0.005 0.0075 Trial 1 Mix 20 ml of Fe 3+ and 20 ml I - solution in a 50 or 100 ml beaker and after making sure that the solution has mixed properly pour into a cuvette. Place the solution in the colorimeter that has been calibrated Press the play button to start the data collection Wait for 200 seconds for the collection to be complete Select a segment from 20 to 45 seconds preferably in the first minute of the reaction Select analyze Choose curve fit Absorbance OK Now write down the value of m or slope of line in the table above Repeat the experiment for trials 2 to 5 Once you have the values you can calculate the order of the reaction Note: The segments from the graph selected for determining the order of rate of the reaction should be identical with respect to the time frame, between the different runs to obtain accurate results. The start time for recording absorbance for all experiments should be the same from the time of mixing of the solutions The time interval 25 seconds or 30 seconds should be exact for all experiments Alternatively you may save all the runs at the same time and import this data into LoggerPro lite and determine the rate on a computer. Logger pro lite is the software that can be installed on your computer to analyze your data. This gives you better final values. Direct download lint of the software. http://www2.vernier.com/download/loggerlite161installer.exe Or the download page, at the bottom of the page you will get options for the different operating systems like Mac and PC http://www.vernier.com/products/software/logger-lite/
Sensor set up Sensor set up Sensor set up Determining rate Analazying using curve fit linear Slope of line = rate of reaction = m Note the order of the reaction is 1 with respect the iodide ions [I - ] and zero with respect to Fe 3+
Calculation: The order can be determined using initial rate method calculation Should give you the order of iodide ions Solve for x x is the order of Iodide ions Similarly solve for y Should give you the order of Fe 3+ ions Solve for y y is the order of Fe 3+ ions Rate = k[fe 3+ ] y [I - ] x Repeat calculation for the different trials performed to complete the lab.