Lab 5 – The Copper Cycle
Brandon Osmond 100578081
Laboratory Partner: Andrew Singh
Date of Experiment: 12th day of February 2015
Date of Submission: 19th day of February 2015
Professor: Ron Motum
Course: CHEM 1131
Table of Contents
Objective 3
Method 3
Equipment 3
Chemicals 3
Safety 3
Observations 5
Redox Reaction 5
Double Displacement 5
Dehydration 6
Double Displacement 6
Redox 7
Numerical Data 7
Calculations 7
Initial Weight of Copper 7
Weight of Copper Produced 8
Per Cent Yield 8
Results 8
Discussion 8
Conclusion 12
Questions 12
References 15
Objective
The objective of this experiment is to build on knowledge of various types of reactions involving copper. The per cent yield of the reactions will also be determined using masses and the provided per cent yield formula in the Chemistry Laboratory Manual (White, J.M 2015).
Method
For a full method, please refer to the Chemistry I (CHEM1131) Laboratory Manual, revised by John McKenzie White pp. 16-20.
Equipment
· Hot Plate
· Beakers
· Stirring Rod
· Steel Wool
· Analytical Balance
· Boiling Chips
· Thermometer
· Fume Cupboard
Chemicals
· Concentrated nitric acid - HNO3
· 3M sodium hydroxide - NaOH
· 6M sulphuric acid - H2SO4
· Methanol – CH4O
· Acetone – C3H6O
· Zinc powder - Zn
Safety
In the event that nitric acid, sodium hydroxide or sulphuric acid comes into contact with eyes or skin, rinse with plenty of water for no less than fifteen (15) minutes. Nitric acid is a harmful and corrosive oxidiser, sodium hydroxide is very corrosive and sulphuric acid is also corrosive. Methanol and acetone are very flammable and should be kept away from a combustion source or flame at all times (White J.M 2015). In addition to precautions taken when handling the chemicals used in this experiment, great care and attention was paid to the reactions and their surrounding environments. For example, in the first redox phase of this experiment, the entire reaction between the copper wire and nitric acid was conducted in a fume cupboard to ensure that all gasses that are produced are removed out of the environment[1]. Safety as such is key, to prevent any sort of unwanted chemicals being contained within the room. Most importantly, the decanting process was conducted in a fume cupboard in the event that a spill occurred, which it did. Thankfully, the solution spilt inside the fume cupboard and not onto the bench, where it could have been uncontained.
It should also be noted in the Chemistry Laboratory Manual that when dehydrating the solution on a hot plate, the solution could start to react violently when heated. The gel-like copper hydroxide does not easily allow oxygen to leave the liquid, which caused the beaker to shift around when bubbles were released. A potential safety hazard could arise where the beaker could leave the hot plate, causing burns and potentially pose an electrical hazard. Had the hot plate not been shut off and let to cool, the beaker could have easily spilt exposing electrical wiring and the electrical hot plate to a water spill in a metal basin. This concern should be brought up in the manual, to avoid any future dangerous situations.
Observations
Redox Reaction
Cu+4HNO3→Cu(NO3)2+2NO2+2H2O
At first, the solution turned from a clear, colourless liquid to a yellow, transparent liquid. As the reaction took place, the solution turned green, clear and a chemical reaction in the form of gas bubbles occurred. In addition, a yellow/green visible gas was produced that appeared to be less dense than air. 100mL of deionised water was added and a gas formed that appeared to be similar to steam of water. A temperature change was observed in the beaker and the solutions colour changed from a green (dark) to a light green, on to blue and lighter blue upon the addition of the 100mL of deionised water.
Double Displacement
Cu(NO3)2+2NaOH→Cu(OH)2+2NaNO3
Upon the addition of three molar sodium hydroxide, a solid formed and settled to the bottom of the beaker. The solid was dark blue in colour, and the liquid in the beaker was settled above the solid. There was no gas or colour change, but with respect to the liquid, there was a tremendous amount of solid formed.
Dehydration
Cu(OH)2→CuO+H2O
The beaker of solution was placed on a prescribed hot plate where it was left to heat, until just before boil. As the solutions temperature rose to approx. 80 degrees centigrade, the beaker began shifting around due to the vitriolic reaction-taking place, in the form of copper oxide. It was clear that bubbles from the bottom of the beaker from the temperature change caused the beaker to move around the hot plate. At this point, the hot plate was switched off and the solution was left to cool. Once cool, the water was decanted from the solution, at which point, a team member tipped the beaker in the fume cupboard, causing the solution to leave the beaker. Some of the remaining solution was recovered and the experiment continued based on the remaining solid and liquid.
Double Displacement
CuO+H2SO4→CuSO4+H2O
Once the majority of water had been removed via a decanting process, the somewhat solid, black precipitate turned red with the addition of six molar sulphuric acid.
Redox
CuSO4+Zn→ZnSO4+Cu
Zinc powder was added to the solution and the reaction was rather violent. A gas was formed and a strong odour came from the reaction, so it was conducted in a fume cupboard. As a final observation, all of the zinc dissolved and the solution remained blue.
Numerical Data[2]
· Weight of Beaker: 112.7585 grams
· Weight of Beaker and copper: 113.2544 grams
· Weight of Copper: 0.4959 grams
· Weight of Crucible: 70.9972 grams
· Weight of Boiling Chips: 0.0320 grams
· Final weight: 71.0331 grams
Calculations
Initial Weight of Copper
x=mbeaker+Cu-mbeaker
x=113.2544g-112.7585g
x=0.4959g
∴the amount of Copper weighed is 0.4959 grams
Where mbeaker+Cu is the mass of the beaker and copper
mbeaker is the initial weight of the beaker
Weight of Copper Produced
x=mf-mi-mbc
x=71.0331g-70.9972g-0.0320g
x=0.00390g
∴the remaining copper weighed 0.00390 grams
Where x is the weight of remaining copper
mf is the final mass in grams
mi is the initial weight of the crucible in grams
mbc is the mass of the preweighed boiling chips
Per Cent Yield
%yield=experimental yieldtheoretical yieldx100%
%yield=0.00390 g0.4959gx100%
%yield=0.00390 x 100%
%yield=0.39%
∴the percent yield of copper in this experiment is 0.39%.
Results
Based on the results obtained, and the occurrences during experimentation, it can be assumed that there will be a significantly less amount of copper at the end of the experiment, than there was at the beginning of the experiment.
Discussion
Though out this experiment, there is emphasis placed on the observation of copper as it cycles through different reactions and changes composition. If the experimentation is completed correctly, the experiment should have a high per cent yield value, this is the amount you started with compared to the final amount. Unfortunately, due to the unforeseen events during this experiment, the results will not be accurate. Throughout the experiment, observational data was described using short sentences, and certain measurements were taken using an appropriate device, an analytical balance.
The initial substance, 0.4959 grams of copper, was cleaned and weighed. The reason that 0.5000 grams of copper was not used, was based on the limitations of the scale, the number was difficult to achieve. More importantly, the mass reading was stable and repeatable, which was good grounds to conduct the experiment. Also, the mass of the beaker was recorded for completing the maths component of this experiment. As observed, nitric acid added to the 250mL beaker containing the copper strand started a reaction, more specifically a reduction-oxidisation reaction, or redox. In this reaction, the copper reacted with the nitrate polyatomic ion found in nitric acid, forming copper (II) nitrate, nitrogen dioxide and finally, the added 100mL of deionised water. This reaction caused the solid copper to degrade and change form from solid to liquid, thus the added nitric acid melted the solid copper. This reaction was expected since the next double displacement reaction occurred, based on the required copper (II) nitrate that was formed in this part of the experiment. A by-product of this reaction was nitrogen dioxide, a yellow, gas that is less dense than air.
As previously mentioned, the previous redox reaction allowed for the next double displacement reaction to take place. A double displacement reaction requires the switching of two different compounds within a reaction. In this case, the formed copper (II) nitrate reacted with added 3 molar sodium hydroxide. The reaction led to the formation of a very dark blue, heterogeneous solution that contained a thick, gel like substance that is heavier than the other compound in the solution, sodium nitrate. By this point in the reaction, the solid copper that was initially weighed out had been involved in the two of the 5 chemical reactions, so it can already be anticipated that some copper has been lost in the process. It should also be noted that in order for a double displacement to take place, both chemical compounds must contain the same charge, in order for the reaction to occur.
In this dehydration reaction, the compound, copper (II) hydroxide was subject to heat, almost to the point of boil. By adding heat to the solution, it can be said that energy is also being added, thus helping the dehydration take place. By adding energy to the solution, hydrogen atoms were removed and a heavy, dark black substance was left. Essentially, the previous dark blue solid had water of hydration removed to form water leaving the black, heavy solid at the bottom of the beaker. The next steps in removing the excess water of hydration and water from the reactions is crucial. As previously mentioned, the overall goal of this experiment is to determine the per cent yield of the copper in the experiment. With this being said, any left over water in the copper sample will not only prolong the drying phase but can ultimately skew your results. Excess water in the copper sample can make the copper heavier than it is which provides an invalid yield.
During the final phases of the experiment as mentioned, removing as much water from the sample is important, not only to speed up drying, but to also improve the results (per cent yield). When transferring the solid copper as result of the final redox reaction, by washing the copper; one is removing any trace of zinc sulphate. Similarly to water, zinc sulphate can add false weight to the copper filled crucible after heating. By rinsing off the water and constantly decanting, it is the goal to only have copper remaining, and a small amount of water that is easily evaporated.
During the experiment, there are many difference sources of error. In the case of this experiment, the beaker having been knocked over while the solution was being decanted was the largest source of error. Had the experiment finished without this occurring, the largest source of visible error would be the loss of copper associated with stirring, boiling and transferring. For example, while dehydrating the copper hydroxide, there was loss where the solid copper had stuck to the stirring rod. This type of error can be avoided simply by reintroducing the copper off the stirring rod, back into the beaker. A second major source of error is during the decanting phases of this experiment. As you decant fluid, it becomes very difficult to minimize loss when the solid is not much heavier than the liquid since it has a difficult time to settle and stay separated. With this being said, the loss associated with decanting the liquids is also a significant factor when completing this experiment. Lastly, error can be introduced into the experiment if various balances are used to record measurements. To reduce error when measuring, one should be sure that the balance is level, fully operational and properly tarred. The scales doors should also be shut when a reading is taking place and the scale will prompt the user with a noise that the reading is accurate and stable. In the case of this experiment, the previously mentioned steps were taken to ensure a high degree of accuracy.
Conclusion
In conclusion, the final per cent yield of the experiment is 0.39%. This yield is incredibly small because of the occurrences during the experiment that were unforeseen. Had the experiment gone to plan, the yield would be much greater with only little error in the means of loss via experimentation.
Questions
1. Define the concept of per cent yield.
The concept of per cent yield can be described as a relation between how much final product is measured and how much was measured to begin with. With this being said, the difference between the two values is calculated, multiplied by 100 to obtain its percentage. Per cent yield is useful when one wishes to determine the amount of loss in an experiment as a percentage.
2. Name two methods of separating materials you have used to date.
Two different types of filtration used to date are the decant method, and the filtration method. Both methods have their respective uses in different situations. Filtration requires the use of a filter that separates solid from liquid where loss is acceptable. Decanting on the other hand, leaves the solid untouched and simply removes a top layer of liquid.