Effect of temperature on extent of browning
Sample Temp (oC) Absorbance after ( ) minutes
Any color changes? (see #11 below)
10. If you experience measuring delays, you will need to control for the fact that the reaction product continues to form while you are waiting to measure it. After measuring the absorbance in tubes 1, 2, 3, 4, and 5, measure them again in reverse order (5, 4, 3, 2, 1) and use the average absorbance for each temperature. 11. If the reaction is proceeding correctly, you should see (with your naked eye} a darkening of the solution. This rusty brown precipitate is benzoquinone, the desired product of the reaction. If you see “cloudiness,” it means you mistakenly picked up particulate matter (sludge) from the bottom of the flask. 12. Plot your values for absorbance as a function of temperature using the graph paper below. If necessary, you may change the absorbance scale on the y-axis to 0.5 and 1.0. Graph 1: Effect of temperature on browning rate
Temperature of water bath (oC)
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Analysis and Discussion 1. At what temperature(s) was the rate of reaction greatest? ____ At what temperature(s) was the rate lowest? ____ Are these observations consistent with the hypothesis about thermal effects you formulated at the end of Part I? ______ What do these observations suggest about the “optimal” range of temperatures for enzyme catalyzed reactions? State your conclusion in the form of a revised hypothesis. HYPOTHESIS A (Revised): The rate of an enzyme catalyzed reactions is greatest at temperatures that are… 2. At the molecular level, what might explain the rate of the enzyme-catalyzed reaction at low temperatures? (Hint: For a reaction to occur, the two reactant molecules must “bump into’ each other. How does temperature effect the motion of molecules?) 3. At the molecular level, what might explain the rate of the enzyme-catalyzed reaction at high temperatures? (Hint: How does temperature effect the molecular structure of enzymes?)