Chemistry 120 Lab 41: Copper Cycle Pre-lab Procedure Design an experiment that changes pure copper into copper nitrate, copper hydroxide, and copper sulfate and then back into pure copper, demonstrating the law of conservation of mass. 1. Acquire 0.4 grams of copper wire and place it in a 200 ml glass beaker. 2. Add 6M HNO3 (Nitric Acid). To form copper nitrate. 3. Add 10ml Sodium Hydroxide (NaOH) at a time to the copper nitrate until litmus paper turns blue and copper hydroxide is formed. 4. Use a vacuum filtration system to isolate the CuOH2 and wash with distilled water. Discard Filtrate. 5. Leaving the copper hydroxide on the filter paper, Add 2M Sulfuric acid (H2SO4) in small increments, until all is dissolved, to the copper hydroxide. 6. Add Zn to the copper sulfate to form Pure copper and Zinc Sulfate 7. Dissolve any excess Zinc with 3M Hydrochloric Acid (HCL) 8. Filter the pure copper out using the filtration system. Lab Report After completing the preliminary tests to determine the reactivity and solubility three copper salts and their reactivity with each other, design an experiment that changes pure copper into copper nitrate, copper hydroxide, and copper sulfate and then back into pure copper, demonstrating the law of conservation of mass. ? Acquired 0.200 grams of copper wire and placed it in a small test tube. ? Added 6M HNO3 (Nitric Acid) a ml at time until there was no more sign of reaction. The reaction was sped by warming the solution gently for 5-10 seconds in a cool flame. Brown gas was evolved and the solution turned a blue green color as the copper was dissolved into aqueous copper nitrate. Cu + 4HNO3 -> Cu(NO3)2 + 2NO2 + 2H20 -Caution: Nitric acid is corrosive avoid skin and eye contact. Wear goggles at all times. ? 10ml of 6M Sodium Hydroxide (NaOH) is added. Then 1ml 6M NaOH added at a time to the copper nitrate until litmus paper turned blue and there was no more sign of reaction. The reaction was sped by warming the solution gently for 5-10 seconds in a cool flame. As copper hydroxide is formed, the solution turned a cloudy blue color and red/brown gas was evolved. Cu(NO3)2 + 2NaOH -> Cu(OH)2 + 2NaNO3 -Caution: the gas evolved is dangerous. Perform this step in the fume hood to avoid breathing it in. ? The insoluble CuOH2 is separated from the excess Nitric Acid and Sodium Hydroxide by placing it in the centrifuge. Remove the excess liquid with a plastic pipette but do not remove any of the blue Copper Hydroxide. Discard the excess material in the sink while running water to dilute the acid. -Caution: be sure the centrifuge is balanced with another test tube filled with the same amount of liquid. Be patient and do not stop the centrifuge early before it stops spinning. ? Added 2M Sulfuric acid (H2SO4) in small increments, until all is dissolved, to the copper hydroxide. Heat was evolved and the liquid turned a clear color. Cu(OH)2 + H2SO4 -> CuSO4 + 2H20 -Caution: Sulfuric Acid is very corrosive avoid skin and eye contact. ? Add Zn to the copper sulfate to form Pure copper and Zinc Sulfate. The solution went from clear to gray. The solution turned warm and gas evolved. CuSO4 + Zn -> ZnSO4 +Cu ? Dissolve any excess Zinc with 3M Hydrochloric Acid (HCL) Zn + 2HCl -> ZnCl2 + H2 -Caution: Hydrochloric acid is corrosive. ? Filter the pure copper out using the filtration system. The aqueous Zinc Chloride will pass through the filter leaving only the rust colored copper. ? The Copper was washed with ethanol to dry it and then weighed on weighing paper. The copper was massed at 0.278g. the excess weight can be attributed to leftover zinc that was not completely dissolved by the HCl and then filtered out. Conclusion: 0.200 grams of copper was changed into copper nitrate, then to copper hydroxide, then to copper sulfate and then back into copper. During the process excess chemicals and materials were not completely removed from the copper and we finished with a mass of copper of 0.278 grams. Laboratory Questions (1) The most important factors to keep in mind is the safety of yourself and your classmates, to not damage any of the lab materials or supplies, and to utilize a frugal amount of lab materials. (2) This experiment is called the copper cycle because you both start and end with elemental copper. This demonstrates that matter can not be created or destroyed, even though the copper is no longer visible during the majority of the lab, if you are patient and accurate in your procedure you can re-isolate the copper. (3) Particle View of Reactions. (4) Percent yield = (starting mass / Final Mass) * 100 (0.200 / 0.278) * 100 = 71.9% (5) The percent yield could be more than 100% if some of the Zinc used in the final steps was not completely filtered out or if the final product was not completely dry before it was weighed. The percent yield could be less than 100% if some of the copper was lost when the Cu(OH)2 was separated from the excess nitric acid when the nitric acid was sucked up into the pipette. chad Microsoft Word - 200812041947379664__e__chem120-boll-copper-cycle.doc
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