Na_2 C_3 H_34 N_2 S_3 O_3 + OCI rigtarrow products Blue food coloring can be oxi
ID: 938226 • Letter: N
Question
Na_2 C_3 H_34 N_2 S_3 O_3 + OCI rigtarrow products Blue food coloring can be oxidized by household bleach (which contains OCI) to form colorless products, as represented by the equation above. A student used a spectrophotometer set at a wavelength of 635 nm to study the absorbance of the food coloring over time during the bleaching process. In the study, bleach is present in large excess so that the concentration of OCI is essentially constant throughout the reaction. The student used data from the study to generate the graph below. Based on the graphs above, what is the order of the reaction with respect to the blue food coloring? The reaction is known to be first order with respect to bleach. In a second experiment, the student prepares solution of food coloring and bleach with concentrations that differ from those used in the first experiment. When the solutions are combined, the student observes that the reaction mixture reaches an absorbance near zero too rapidly. In order to correct the problem, the student proposes the following three possible modifications to the experiment. Increasing the temperature Increasing the concentration of the food coloring Increasing the concentration of the bleach Circle one proposed modification above that could correct the problem, and explain how that modification increases the time for the reaction mixture to reach an absorbance near zero. In another experiment, a student wishes to study the oxidation of red food coloring with modify the original experimental procedure to respect to the red food coloring with bleach. How would the student need to modify the original experimental procedure to determine the order of the reaction with respect t to the red food coloring?Explanation / Answer
a. Sinve th graph of ln (absorbance) vs time (s) gave us a straight line, this reaction is a first order reaction.
b. To modify the reaction mixture, the student would be,
- Increasing the concentration of the food coloring
The reaction is observed to reach zero absorbance fast, that means the concentration of substrate that is the food color is much lower than the oxidising reagent bleach. All of the substrate gets oxidized in no time and gives a zero absorbance value. To change this the student has to add more substrate so that the bleach becomes the limiting reagent and reaction time increases.
c. Similar to the experiment desribed here, the student has to use red food coloring as the substrate and bleach as the oxidizing agent. Absorbance readings are measured at regular intervals and plotted as absorbance vs time for zero order, ln(absorbance) vs time for first order and 1/absorbance vs time for second order reaction kinetics. The graph where we get a straight line is the order of reaction.
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