Briefly explain whether the following procedural errors would result in either a
ID: 856351 • Letter: B
Question
Briefly explain whether the following procedural errors would result in either an incorrectly high or in an incorrectly low calculated percent Cu recovery for this experiment. (a) The solution was not basic when it was heated in Part III. (b) A slightly blue solution was decanted from the Cu in Part V. (c) In Part V. the water in the beaker boiled away, exposing the evaporating dish to excess heat. 2. You used both HNO3and H2SO4 solutions in this experiment. Briefly answer the following questions. (a) Why couldn't you substitute 3M H2SO4 for concentrated HNO3 in Part I? (b) Why couldn't you substitute concentrated HNO3 solution for 3M H2SO4 in Parts IV and V? 3. When performing Part V. a student used Equation 7 to calculate the precise mass of Zn needed to reduce the [CU(H2O)6]^2+ions in his solution. His calculated percent recovery of Cu was very low. Briefly explain what error might account for his low recovery of Cu.
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3. Calculate the number of moles in: (1) 2.1 g of salicylic acid (GMM: 138 g mol^-1) (2) 4.0 mL of acetic anhydride (GMM: 102 g mo ^-1.density: 1.08 g ml^-1) 4. Based on the amounts of reagents specified in this experiment, calculate the theoretical yield of aspiri (GMM: 180 g mol ^-1) in terms of: (1) moles (2) grams 5. Briefly explain the purpose of the FeCl3 test. What does a positive FeCl3 test signify? What observation corresponds to a positive FeCl3 test?Explanation / Answer
1. If we go through the experiment of copper recovery the principle is A solution of copper sulfate will be reacted with zinc metal. Zinc metal replaces the copper in solution and metallic copper would be precipitated . The experimental procedure errors can influence the yield of the reaction in following ways:
A) If the solution is not basic enough, the calculated Cu recovery would be low. The Cu(OH)2 would be in solution, thus more amount of unhydrated CuSO4 would be present that would not undergo reaction with zinc and would lower the calculated Cu of the experiment.
B) The slightly blue colour of solution is due to the presence of Cu(H2O)6 which is not reduced, therefore decanting would lower the Cu recovery amount than the actual Cu content.
C) the water in the beaker boiled away, exposing the evaporating dish to excess heat would convert the hydroxide into copper oxides then the Cu calculated would be incorrectly higher than the actual recovery of Cu because it has mass of oxygen too.
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