CH302 - Experiment 6 Post Lab PDF

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Experiment 6 – The Reactions of a Copper Cycle The objective of this experiment was to observe both the chemical and physical changes that occur when the metal, copper undergoes a series of chemical reactions. This series of reactions produced different copper compounds (compared to the original) and the other objective was to restore the copper to original state, aiming for a high percent recovery, target goal being around 80 percent. The first reaction in the series of reactions involved adding HNO 3 to solid copper to dissolve the copper ions. During the reaction, it was observed that when two drops of the 16.0M HNO 3 was added to the solid copper, there was an immediate reaction that involved chemical changes: the release of brown gases, while the HNO3 began turning a blue-green color, there was a physical change: decrease in volume as gases were released. It’s important to note that it was necessary to conduct this first reaction involving the HNO3 in the fume hood because the gaseous products would be toxic if inhaled in large amounts. This reaction was an exothermic reaction as the dissolving of copper occurred spontaneously, and heat was released when HNO3 and solid copper came in contact. Afterwards, as distilled water was added to the solution, a resulting physical change: the coloration came to look like a light-cyan as the volume of the solution increased. The second reaction of the series involved the addition of 30ml of NaOH. When the NaOH was added to the solution, the original darkish royal blue color reappeared and a viscous substance formed, a chemical change, and the volume of the solution increased, being a physical change. This reaction was an exothermic reaction as the reaction occurred spontaneously. The following third reaction involved the heating of the solution which resulted in the formation of small particles of copper (a chemical change) and the solution turned a murky blue color, a physical change – the overall process being exothermic as it occurred spontaneously. Afterwards, the near-boiling de-ionized water was added to the solution (an endothermic process as heat, or energy is required to settle t the copper.) The next reaction (fourth reaction) incorporated the addition of 15ml of 6.0M H 2SO4 which resulted in the particles of copper dissolving, a chemical change, and the clear blue color was regained, being a physical change due to the lack of copper. The process was an exothermic reaction because the reaction was spontaneous and required no input of energy to start. For the last reaction of the series, aluminum and HCl was added to the solution, and then the solution of heated. When the aluminum and HCl were added to the solution, a chemical change underwent as the aluminum began to dissolve, and copper began to form as the solution was heated. A resulting physical change due to the chemical was that the solution became a clear-blue color. This process was an endothermic process as an input of energy was required (the act of heating up the solution.)

In the final reaction, the recovered copper was washed with water in order to remove any remaining soluble aluminum. Following the washing of water, the recovered copper was washed with ethanol because copper is less soluble in ethanol than it is in water so when decanting the solution, more amounts of any remaining aluminum would be decanted along with the ethanol. When heating the solution, a steam bath was used in place of a hot plate, because the heat can be better controlled through the steam bath, also, a steam bath was used instead of a hot plate to prevent the oxidation of copper during the process of drying the wet copper. Thus heating the “wet” copper over a steam bath would be the more probably choice compared to the hot plate. The Law of the Conservation of Mass states that in a closed system in terms of transferring of matter and energy, the mass of the system must remain constant or conserved or time. The results obtained from the experiment did support the Law of Conservation of Mass despite the fact that the experiment was conducted in an open system, the final percent copper recovery came out to be 87.71%. Percent recovery indicates how much of the original mass was recovered throughout the process of reactions; perfectly recovered matter would be 100% recovery. When comparing the experimental results with the desired results, the experimental results were reasonably set, as it’s a given that some copper was lost in the cycle of reactions. The finished copper product appeared to be in a solid form that resembled a sort of powder, though more viscous. The physical change in appearance is due to the set of reactions that broke apart the copper solid, and restored the copper solid at a later time. Despite the copper being mostly restored, the original form of the copper was not retained. (All of the dissociation and restoration processes being described in the earlier reactions.)...