Chemical Reactions of Copper and Percent Yield AP Chemistry.
Chemical Reactions of Copper and Percent Yield
I. Purpose: The purpose of the lab is to use a piece of copper in a series of chemical reactions and ultimately recover as close to the same amount of copper as possible. We will learn about percent yield. Also, it can help learn more about typical transition elements.
II. Pre-Lab Questions:
1. Give and example, other than the ones listed in this experiment, of redox and metathesis reactions.
Redox reaction: Br2 + 2OH– à BrO– + Br– + H2O
Metathesis: Na2SO4 + BaCl2 à BaSO4 + 2 NaCl
2. When will reactions proceed to completion?
Reactions are considered complete when at least one of the reactants is completely spent.
3. Define percent yield in general terms. Percent yield relates the amount of product you recover to the amount of that same substance that you started with. Also, it relates the theoretical stoichiometrical yield to the actual yield.
4. Name six methods of separating materials. Common methods of separation are filtration, sedimentation, decantation, extraction, chromatography, and sublimation.
5. Give criteria in terms of temperature changes for exothermic and endothermic reactions. In an exothermic reaction, the solution increases in temperature (because the system releases heat energy). In an endothermic reaction, the solution decreases in temperature (because the system absorbs heat energy).
6. If 3.35 g of Cu(NO3)2 are obtained from allowing 2.25 g of Cu to react with excess HNO3, what is the percent yield of the reaction? Since the theoretical yield is 6.64 grams of Cu(NO3)2, the percent yield is 50.45%.
7. What is the maximum percent yield in any reaction? Since matter cannot be created in a reaction, the maximum percent yield is 100%.
8. What is meant by the terms decantation and filtration? Decantation is the process of separating a liquid from a solid by gently pouring the liquid from the solid so as not to disturb the solid. Filtration is the process of separating a solid from a liquid by means of a filter which allows the liquid to pass through but not the solid.