![]() Note: The following data was obtained using the spectrometer. Once the reaction order is calculated, you can use the appropriate rate equation to solve for the rate constant, assuming the concentration is known.įor 1st Order reactions: ln(t/0) = -ktįor 2nd Order reactions: 1/t – 1/0 = kt Setting the ratios equal to each other gives:ĭetermine t for the two concentrations and solve for x to find the reaction order with respect to the dye. Taking the ratio of each and cancelling k gives The rate equations with respect to dye concentrations for both reactions can also be written as: Taking the ratio of the above rate equations: Rate is also given by the following equation: Rate is proportional to concentration, ^n Using the time it takes for the blue color to disappear, and knowing that the concentration of the second is double that of the first reaction, the reaction order with respect to the blue food coloring concentration can be determined. The purpose of this demo is to experimentally determine how the dye concentration affects the rate. Repeat the procedure to conduct a second trial with a new food colored solution and another 10 mL sample of bleach. Store the run by clicking the File Cabinet icon or choosing Store Latest Run from the Experiment menu. time, showing a gradual decrease in absorbance. To continue collecting after 200 seconds, click the start collection button and select “Append”. Absorbance data will be plotted every second for 200 seconds.Place the cuvette in the spectrophotometer. Swirl the reaction mixture with a plastic transfer pipet and use the pipet to fill the cuvette ¾ full of the reaction mixture. DO THIS QUICKLY: Add the 10 mL of bleach to the beaker of food coloring solution.Remove the cuvette from your spectrophotometer and pour out the solution.Collect absorbance-time data for the reaction of food colored solution and bleach. The default settings are suitable for this experiment. The wavelength of maximum absorbance (l max) will be selected. Click the Configure Spectrometer button on the toolbar (visible spectrum on a graph).To set up the data collection mode for the reaction of food coloring and bleach:.Store the run by clicking the File Cabinet icon or choosing Store Latest Run from the Experiment menu.Note that one area of the graph contains a peak absorbance, and there may be other lesser peaks that characterize this substance. A full spectrum graph of the solution will be displayed. Fill the cuvette ¾ full with the solution and place it in the spectrophotometer. Empty the blank cuvette and rinse it twice with small amounts of the food colored solution.Determine the maximum wavelength for the food colored solution and set up the mode of data collection. When the warmup period is complete, select Finish Calibration. Place the blank in the spectrophotometer make sure to align the cuvette so that the clear sides are facing the light source of the spectrophotometer.Choose Calibrate from the Sensors menu of LabQuest or the Experiment menu of Logger Pro.Prepare a blank by filling an empty cuvette ¾ full with distilled water.Use the Spectrometer to determine the length of time it takes for the absorbance to reach zero. Add the bleach and measure the amount of time it takes for the color to disappear.Īlternatively: keep the concentration of the dye constant (make one solution and split it in half) and add different amounts of bleach (10 mL and 20 mL) to observe the affect of the bleach concentration. Place one solution on the stir plate and add the stir bar. Take 100 mL of the above solution and dilute with 100 mL to get a solution of half the concentration.ġ. Add one drop of food coloring to 300 mL waterĢ. *Located in the drawers opposite the bin storage shelvesġ. Optional: Vernier Spectrometer - requires Logger Pro software*.Stir plate (located in top drawer opposite the chemical storage cabinets or on the bench).From this, the reaction order for concentration of blue food dye is determined. Bleach is added to both samples and the time until the blue color disappears is recorded. Demonstrations › Chemical Kinetics › 14.2ġ4.2 Effect of Concentration on Rate of Reaction/Reaction Orderĭescription: Two samples of blue food dye in water, one with double the concentration of dye.
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