The objectives of this experiment were to watch and take note of the chemical and physical changes of metallic copper going through a number of chemical reactions that result in a number of different compounds before the copper returns to its original metallic form. The objective of the experiment includes becoming familiar with standard laboratory practices used to separate and purify products and the concept of percent recovery. The objective was also to balance and classify the different reactions involved in the cycle and to identify and write the formula unit, total ionic and net ionic equations for the precipitation and acid-base reactions in this experiment. The first reaction that occurred was when a piece of copper was added to a solution of HNO3. This resulted in a green solution that let off brown fumes. These brown fumes were from the oxidation of the copper and left a clear blue solution. The next reaction occurred when 30.0 mL of 3.0M NaOH was added. This caused the clear blue solution to turn into a bright blue, gelatinous solution. This was caused by the addition of the base, which resulted in the precipitation of the copper hydroxide. Heat was added to the solution, which caused the hydrogen to leave, and the solution to form a black precipitate. Fourthly, the addition of H2SO4 caused the solution the solution to turn into a clear light blue solution, copper sulfate. Lastly, when the Al was added to the solution the solution turned red and fizzed and turned clear. This was caused by the reduction of the copper cations by the Al to yield metallic copper. The unreacted Al was removed by the addition of the hydrochloric acid.
These reactions are endothermic because they needed to be heated up to occur. The first reaction was done in the hood because when the copper and the HNO3 were combined it resulted in brown fumes being let off. This is an indication of the oxidation of the copper. The copper is washed with water to remove any further soluble Al from it. Ethanol was then used to wash the copper again in order to speed up the drying process. The ethanol ensures that the copper sample does not contain excess water. The steam bath was used instead of the hot plate in order to ensure a gradual drying of the substance, which helps produce a more pure and unaffected product.
The Law of Conservation of Mass states that in any reaction the mass of the reactants will equal the mass of the products. The amount of copper left after the experiment indicates some loss but it can be attributed to inefficient lab practice. Some loss may have occurred when decanting. The percent recovery of copper is used to determine how much of the original pure copper was recovered at the end of the experiment. I recovered 43.67% of the original copper. My results are far too low. This may have occurred due to overheating of the solutions as well as up taking copper in the decanting process.
At the end of the experiment my product appeared to be a powdery dark red substance. This change in appearance may have been caused by reduction of the copper to copper metal.