University:
Cornell University
Course:
CHEM 2070 | General Chemistry I
Academic year:

2019
Views:

158

Pages:

2
Author:

David Lopez

CHEMISTRY Question 5 Na₂CH SOCI products blue colorless 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 graphs below. 0.9 0.0 45 0.8 -0.5 40- 0.7- -1.0 35 0.6 30- -1.5 0.5 -2.0 0.4 20- -2.5 0.3 0.2 -3.0 10- 0.1 -3.5 5 0.0. -4.0 0 0 20 40 60 80 100 Time (s) Graph I Time (s) 0 20 40 60 80 Graph III (a) Based on the graphs above, what is the order of the reaction with respect to the blue food coloring? 0 20 40 60 80 100 Time (s) Graph 11 100 First order I point is earned for the correct order. (b) The reaction is known to be first order with respect to bleach. In a second experiment, the student prepares solutions 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 the 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. CHEMISTRY Question 5 (continued) ["Increasing the concentration of the food coloring" should be circled.] If the initial concentration of blue food coloring is increased, then more time is required (regardless of the reaction order indicated in part (a)) for the bleach to oxidize the additional blue food coloring. I point is carned for the correct choice. I point is earned for a correct explanation. (c) In another experiment, a student wishes to study the oxidation of 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 to the red food coloring? The spectrophotometer should be set to a different wavelength. I point is earned for a correct answer.