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Experiment 17: Chemical Equilibrium
PURPOSE
The purpose of this experiment was to examine the reaction that certain solutions have when an acid or base is added. Observing the color after a certain amount of the acid or base is added to discover when the reaction is at chemical equilibrium. Temperature and volume of the container used are also changes in the conditions that will effect the reaction. Acids, Bases, and the equilibrium of a reaction were the main topics in chapters 17 and 18 in Chemistry 103, and this experiment enhanced the viewing of these sort of reactions to the students in this course.
PROCEDURE
The procedure followed for this experiment can be found in the lab manual: Sprague, Alexander, Padolik, Steffel, Laboratory Experiments for First Year Chemistry, 5th ed. pp. 17-3 to 17-6.
RESULTS
The results for this experiment can be found on the two report sheets as well as on the carbon copy paper included in this packet.
DISCUSSION
This experiment may have had a lot of errors because there was a lot of measuring out perfect amounts and using your own judgment in deciding when a color change is completed. When adding a solution until a reaction occurs completely, there may an error in the calculated amount of solution added. It was no to difficult, though it was hard to decide on what the color was because sometimes there was such a minuet change. This may have caused the results to be off a little but not too much. Here are some answers to the questions asked in the lab manual.
A. 1) For the first section of part A, when you add NaOH to Cr2O72-, that is a forward reaction, and when you add HNO3, that is the reverse reaction. It is the opposite for the second section of part A.
B. 1) The cobalt solution was the most extensive and the chromium solution was the least extensive.
2) The cobalt solution had the larger equilibrium constant and the chromium solution had the smallest equilibrium constant.
3) There is no definite conclusion that can be made because the experiment was only done at room temperature and no chloro complex formed. Therefore, if the experiment was done again at a different temperature and a chloro complex formed, we could make a conclusion based on those results.
4) In the mixture containing the cobalt and copper, the chloro complex for the cobalt formed first, and yes, this does agree with the previous conclusions about the positions of the equilibrium for the reactions.
5) The two equations have the same equilibrium constant.
C. 1) For test tubes 3 and 5, the addition of the solution caused the reaction to move in reverse, and for test tube 4, the reaction was forward.
2) The reason for comparing test tube 5 to test tube 2 was because test tube was mixed with 1 mL of distilled water, and when the AgNO3 was added to test tube 5, the NCS- was removed to form insoluble AgNCS. Therefore the solution in the test tube was distilled water and cobalt.
3) The reaction of equation 17-9 is endothermic.
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