Purpose
The purpose of this lab is demonstrate the use of the conservation of mass through a series of chemical reactions. This experiment would involve the use of copper (Cu) in a series of reactions that when finished, should equal the same amount of mass as when first started.
Copper Quantitative and Qualitative Data
Quantitative Data
Initial Mass of Copper 2.004 grams
Mass of Evaporating Dish 50.165 grams
Mass of Evaporating Dish and Copper 57.01 grams
Mass of Recovered Copper 6.845 grams
Mass of Evaporating Dish 50.165 grams
Mass of Evaporating Dish and Copper 57.01 grams
Mass of Recovered Copper 6.845 grams
Qualitative Data
Reactions
Cu + HNO 3 - The solution became blue. All of the copper in precipitate form has been removed. Nitrogen gas was formed.
Cu(NO3)2 - NaOH - A blue precipitate was formed. The solution was thick. The blue precipitate collected at the bottom of the beaker
Cu(OH)2 - A black solution was formed. After being heated, the solution turned into water and a black precipitate. All of the black precipitate would collect at the bottom because it is denser than water.
CuO + H2SO4 - The solution turned from a black solution into a greenish blue solution. There were no signs of any solids remaining
CuSO4 + Zn - Zinc solfate is formed. The reaction caused bubbles to appear. After being rested, the solution (copper) was a maroon like color. It sand to the bottom of the beaker.
Cu(NO3)2 - NaOH - A blue precipitate was formed. The solution was thick. The blue precipitate collected at the bottom of the beaker
Cu(OH)2 - A black solution was formed. After being heated, the solution turned into water and a black precipitate. All of the black precipitate would collect at the bottom because it is denser than water.
CuO + H2SO4 - The solution turned from a black solution into a greenish blue solution. There were no signs of any solids remaining
CuSO4 + Zn - Zinc solfate is formed. The reaction caused bubbles to appear. After being rested, the solution (copper) was a maroon like color. It sand to the bottom of the beaker.
Net Ionic Equations
(NIE = Net Ionic Equation)
1) Cu(s) + 4HNO3(aq)→ Cu(NO3)2(aq) + 2NO2(g)+ 2H2O(l)
NIE: Cu(s) + 4H+(aq) + 2NO31-(aq)→ Cu2+(aq) + 2NO2(g) + 2H2O(l)
2) Cu(NO3)2(aq) + 2NaOH(aq)→ Cu(OH)2(s) + 2NaNO3(aq)
NIE: Cu2+(aq) + 2OH-(aq)→ Cu(OH)2(s)
3) Cu(OH)2(s)→ CuO(s) + H2O(l)
NIE: Same
4) CuO(s) + H2SO4(aq)→ CuSO4(aq) + H2O(l)
NIE: CuO(s) + 2H+(aq)→ Cu2+(aq) + H2O(l)
CuSO4(aq) + Zn(s)→ Cu(s) + ZnSO4(aq)
5) CuSO4(aq) + Zn(s)→ Cu(s) + ZnSO4(aq)
NIE: Cu2+(aq) + Zn(s)→ Cu(s) + Zn2+(aq)
1) Cu(s) + 4HNO3(aq)→ Cu(NO3)2(aq) + 2NO2(g)+ 2H2O(l)
NIE: Cu(s) + 4H+(aq) + 2NO31-(aq)→ Cu2+(aq) + 2NO2(g) + 2H2O(l)
2) Cu(NO3)2(aq) + 2NaOH(aq)→ Cu(OH)2(s) + 2NaNO3(aq)
NIE: Cu2+(aq) + 2OH-(aq)→ Cu(OH)2(s)
3) Cu(OH)2(s)→ CuO(s) + H2O(l)
NIE: Same
4) CuO(s) + H2SO4(aq)→ CuSO4(aq) + H2O(l)
NIE: CuO(s) + 2H+(aq)→ Cu2+(aq) + H2O(l)
CuSO4(aq) + Zn(s)→ Cu(s) + ZnSO4(aq)
5) CuSO4(aq) + Zn(s)→ Cu(s) + ZnSO4(aq)
NIE: Cu2+(aq) + Zn(s)→ Cu(s) + Zn2+(aq)
Calculations
Final Mass of Copper
Mass of evaporating dish and copper - Mass of evaporating dish = Mass of copper
57.01 grams - 50.165 grams = 6.845 grams is the mass of copper
57.01 grams - 50.165 grams = 6.845 grams is the mass of copper
Initial Moles of Copper
Initial Mass of copper x (moles of copper/molars mass of copper) = Initial moles of copper
2.004 grams Cu x (1 moles of Cu/63.564 grams Cu) = 0.0315 moles Cu
2.004 grams Cu x (1 moles of Cu/63.564 grams Cu) = 0.0315 moles Cu
Final Moles of Copper
Final mass of copper x (moles of copper/molar mass of copper) = Final moles of copper
6.845 grams Cu x ( 1 mole Cu / 63.564 g Cu = 0.1077 moles Cu
6.845 grams Cu x ( 1 mole Cu / 63.564 g Cu = 0.1077 moles Cu
Percent Yield
Percent Yield = (moles of copper recovered/initial moles of copper) x 100
(0.1077 moles Cu/0.0315 moles Cu) x 100 = 341.9%
(0.1077 moles Cu/0.0315 moles Cu) x 100 = 341.9%
Conclusion
The goal of this lab was to see if the mass of copper would be same after going through a series of chemical reactions. The initial mass of the copper was 2.004 grams. After all of the chemical reactions have finished, the final mass of copper was 6.85 grams. These masses differ quite tremendously. The initial and final moles of Copper should have also been the same. The initial moles of copper was 0.0315 grams. The final moles of copper was .1077 moles. This information also differs. There was a significant amount of moles in surplus in comparison to the moles of the final product and the initial product. The percent yield was calculated at 341.9%.
Discussion of Theory
The basis behind this experiment is the law of conservation of mass. The law of conservation of mass says that matter can neither be created or destroyed. The result of this copper lab should have been that the mass of the initial copper and the mass of the final copper equals each other. In this lab, each group had the initial mass of the copper close to 2.00 grams. There should have only been little deviation from 2.00 grams. In our case, my group measured out 2.004 grams of copper. After putting the copper through many chemical reactions and phase changes, the final mass of the copper was 6.845 grams of copper. This result defies the law of conservation of mass. The final weight should have been 2.004 grams of copper. The results deviated from the weight of copper by 4.841 grams. This should have been impossible. The most probable reason for this result is the abundance in the sources of error throughout the experiment. Whether it be miscalculation or careless mistakes, the results were altered in some way that differs from the law of conservation of mass. The most probable source of error must have been that there were still some solid zinc that did not react with the copper sulfate. This could have drastically increased the final weight of the copper.
Sources of Error
There were many sources of error present throughout this experiment. This could be said due to the overwhelming difference in mass and mole of the final and initial moles and mass. At the start of the lab, each group was to measure as close to 2 grams of copper as possible. A source of error that could be present at this time could have been that the scale was not properly calibrated, thus throwing off the weighted measurement. Another error at this time could be that it was not 2 grams. Most of the group’s measurement deviated from the measurement of 2 grams by less than 0.005 grams. Even this small deviation from the ideal amount could cause a difference in calculations. Many errors would follow. One of the error occurred when testing the pH. The pH tester was suppose indicate a color that matches the number 13. The problem was that there was not a 13 on the scale. This may have affected the results due to the lack of acidity. During the stage when each groups were to heat their beaker with their mixture in it, the heating was considerably inconsistent. The beaker was to be kept on the heater for 5 minutes, starting when it begins to boil. The beaker would take a while in order to start heating up. The knob that was controlling the heat was constantly turned up and down due to the violent bubbling. The time it took to heat did not reach 5 minutes. This could affect the results dramatically. Following the heating, there were some of the solution that was on the side of the beaker. A member of the group would use droplets of water to spray down the solution from the sides of the beaker. Doing this added more water to the solution which could have altered the results. After this process, there was a wait time of 5 minutes. The group may have not waited long enough to let all of the product reach to the bottom of the beaker. Another error would be caused during the decanting process. When decanting the solution, it was hard to extract all of the water from the solution. This surplus of water may have resulted in the greater mass and moles of the final solution. In addition the errors above, another source of error may have came from the final weighing process. One source of error would be the inaccurate calibration. Another would be that inside the evaporating dish, there was a crusty, gelatin-like substance that surrounded the dried up solution. There mere weight of this substance could be enough to alter the final weight of the product.
Post-Lab Questions
1) Th product of the reaction between copper and nitric acid in step 2 is placed on ice because it is needed to control the temperature of the reaction. If the product is not cooled, the reaction would be too violent to deal with. The cooling of the solution is also needed to speed up the process of the formation of a solid product.
2) Double replacement reaction occurred in step 4. Dehydration reaction occurred in step 7. Single replacement reaction occured in step 9.
3) The reaction of excess zinc with sulfuric acid is a critical step in this investigation. This reaction is essential because it makes sure that there is not any solid forms of zinc. If it is solid, it would not be able to properly react with the sulfate. There would be some problems that would arise due to the incomplete reaction. If this reaction were to not have occurred zinc would still be in solid form. Since the solution of zinc sulfate is an aqueous solution, the zinc could not be in the form of a solid. The zinc in the solid form would contribute to the weight when measuring the weight of the final copper precipitate. This would increase the final mass of the copper, which would deviate from the initail mass of copper.
4) When the CuO was washed, the ions that were removed were the excess hydroxide ions. They could have remained after all of the copper reacted from the reaction before it.
5) After adding the sulfuric acid (H2SO4) to the beaker, the copper ended up with a copper ion with a 2+ charge.
6) The ions that were removed when the precipitated copper was washed was the zinc ion. Using the reaction CuSO4(aq) + Zn(s), the product of the net ionic equation can be found in order to determine which ion was removed.
2) Double replacement reaction occurred in step 4. Dehydration reaction occurred in step 7. Single replacement reaction occured in step 9.
3) The reaction of excess zinc with sulfuric acid is a critical step in this investigation. This reaction is essential because it makes sure that there is not any solid forms of zinc. If it is solid, it would not be able to properly react with the sulfate. There would be some problems that would arise due to the incomplete reaction. If this reaction were to not have occurred zinc would still be in solid form. Since the solution of zinc sulfate is an aqueous solution, the zinc could not be in the form of a solid. The zinc in the solid form would contribute to the weight when measuring the weight of the final copper precipitate. This would increase the final mass of the copper, which would deviate from the initail mass of copper.
4) When the CuO was washed, the ions that were removed were the excess hydroxide ions. They could have remained after all of the copper reacted from the reaction before it.
5) After adding the sulfuric acid (H2SO4) to the beaker, the copper ended up with a copper ion with a 2+ charge.
6) The ions that were removed when the precipitated copper was washed was the zinc ion. Using the reaction CuSO4(aq) + Zn(s), the product of the net ionic equation can be found in order to determine which ion was removed.