For experiment 1:
· Measure, using a mass balance the required amount of lab sample Copper Oxide and place in a pre-weighed test tube.
· Clamp this tube above the Bunsen as shown in the diagram.
· Into the clamped test tube place a tube containing a small piece of cotton wool soaked in ethanol. (This converts the methane passing through into a hydrogen-like gas).
· Attach the other end of the tube to a gas tap and slowly turn on the gas, as to not blow out the Copper Oxide.
· Leave the gas running for a minute or so to flush out the oxygen in the tube.
· With a splint light the excess gas at the end of the test tube.
· Heat the Copper Oxide for 5-10 minutes depending on the amount.
· Then turn off the Bunsen and wait for the test tube and contents to cool in a stream of hydrogen, as to not let the hot Copper react with the oxygen in the air.
· Once the test tube is cool weigh it, and record the results.
· Clamp the test tube again and heat for 2-5 minutes then wait for it to cool as before.
· Weigh it once more to check that the mass is the same. If so, the experiment is complete. If not, heat the test tube until the mass is the same.
· Repeat the experiment with the other masses off Copper Oxide.
For experiment 2:
· Fill a crucible three-quarters full of Copper Carbonate.
· Place this on a pipe-clay triangle, which will rest on top of a tripod.
· Heat the crucible and its contents strongly for 10 minutes with a Bunsen burner, while carefully stirring the Copper Carbonate with a spatula.
· Once all the powder has changed from green to black turn off the Bunsen and allow the crucible to cool before weighing.
· Resume heating for a couple of minutes and weigh again.
· If the mass is the same as before the experiment is complete, if not re-heat the crucible and its contents.
· You are now left with your second sample of Copper Oxide.
· It needs to be reduced and should be done so exactly as in the first experiment but instead of using a lab sample use the sample that has just been produced.
For experiment 3:
· Weigh out the required amount of Copper powder and place in a crucible.
· Put this on a pipe-clay triangle, on top of a tripod.
· Heat strongly for 15 minutes or more.
· Once the powder has turned black remove from heat and wait to cool.
· Weigh the crucible and its contents and resume heating for 5-10 minutes until constant mass has been achieved.
· Record the results and repeat with other masses of Copper powder.
· From the results of all 3 experiments we can perform fairly simple calculations based on the fact that the RAM of Copper is 64 and the RAM of Oxygen is 16 to find out the ration of Copper to Oxygen in the three different samples.
Safety:
· As we are dealing with heat during all three experiments aprons and goggles should be worn at all times.
· Heatproof mats should also be used in case of any spillage.
· Care should be taken while handling a hot crucible, test tube or the contents of either.
Obtaining
· The results acquired for the first experiment (the lab. sample of Copper Oxide) are as follows:
· The results for the second experiment (Copper Oxide produced from Copper Carbonate) are as follows:
· Finally the results for the third experiment (heating Copper powder in air) are as follows:
Analysis
Experiment 1:
Point chosen from line of best fit - (1.25, 0.35)
Copper Oxygen
1.25g 0.35g
RAM = 64 RAM = 16
Moles = Mass of Copper Mass of Oxygen
RAM RAM
Moles = 0.01953125… Moles = 0.021875
Ratio = 0.021875
0.01953125
Ratio = 1: 1.20
Therefore giving a formula of CuO
Experiment 2:
Point chosen from line of best fit - (0.93, 0.25)
Copper Oxygen
0.93g 0.25g
RAM = 64 RAM = 16
Moles = Mass of Copper Mass of Oxygen
RAM RAM
Moles = 0.01453125 Moles = 0.015626
Ratio = 0.015626
0.01453125
Ratio = 1: 1.08
Therefore giving a formula of CuO
Experiment 3:
Point chosen from line of best fit - (1.00, 0.04)
Copper Oxygen
1.00g 0.04g
RAM = 64 RAM = 16
Moles = Mass of Copper Mass of Oxygen
RAM RAM
Moles = 0.015625 Moles = 0.0025
Ratio = 0.015625
0.0025
Ratio = 6.25: 1
Therefore giving a formula of Cu6O
Conclusions:
Experiments 1 and 2:
· From the graphs and calculations I can confidently say that the formula of both these samples of Copper Oxide is: CuO
· Copper bonds ionicaly with Oxygen as is shown below:
· All of the points were close to or on the line of best fit, showing positive correlation and a definite trend/pattern (as the mass of Copper produced increases so to do the mass of Oxygen lost).
· The scientific knowledge behind this is The Law of Constant Composition. This states that as long as the compound is pure its proportion of elements will remain unchanged. Furthermore if these proportions are changed the compound formed will be different to that of the original compound. No amount of heating can change an element’s electron arrangement and therefore it follows that no amount of heating can change the formula of a compound.
· My experimental results prove this law.
· Additionally my prediction: I believe that the formula of Copper Oxide will remain the same regardless of how it is prepared, agrees with my results and conclusions.
· Through my work I am now able to make a more general prediction; the formula of any compound, not just Copper Oxide, will remain the same regardless of how it is prepared.
Experiment 3:
· The calculations from the graph for this experiment gave the formula of this sample of Copper Oxide as: Cu6O
· This result is almost definitely incorrect so we can come to no conclusions for this experiment.
All the results followed this same pattern.
Evaluation
· Overall I believe that the evidence I obtained during these experiments is fairly reliable.
· For the first experiment (the lab sample of Copper Oxide) there were no major anomalies because all the values followed the general trend on the graph.
· The second experiment (reducing Copper Oxide made by Copper Carbonate) was extremely accurate with all the points being on or very close to the line of best fit.
· Finally, the third experiment (heating Copper powder in air) was the only major anomaly.
· The reasons for this is that when the Copper powder was strongly heated in the crucible it solidified, therefore not allowing the un-reacted Copper powder at the bottom of the crucible to react with the Oxygen in the air.
· This is the only possible explanation because all the results show the same trend and the fact that all the results are so drastically wrong. This rules out experimental error because this would not account for such a major anomaly.
· On the other hand, experimental error was to blame for the lack of excellent accuracy for the first experiment. In this experiment masses of test tubes and chemicals were only being weighed to 2 decimal places. Weighing to 4 decimal places would obviously improve the accuracy of the experiment. The percentage error of both is showed below:
- 2d.p. balance weighs to +/- 0.005g
- and say we wanted to weigh by difference a mass of 0.1g
- so 0.010g x 100% = a 10% error
0.1g
- 4d.p balance weighs to +/- 0.00005g
- and say we wanted to weigh by difference 0.1g again
- so 0.00010g x 100% = a 0.1% error
0.1g
· Using bigger masses of chemicals is another way (the first being a more accurate mass balance) to increase the accuracy of this experiment.
· The accuracy of the actual procedure is another place where slight errors are likely to occur. For example, if the Copper had not been left to cool for long enough in the stream of Hydrogen it may have re-reacted, while still hot with the Oxygen in the air to form Copper Oxide.
Improvements:
· To improve the first two experiments one should use a wider variety of masses and if possible repeat each mass to take a better average, which will give more accurate results.
· But I believe that for these first two experiments there is a better, more accurate method that one could perform:
-Set up the apparatus as shown above and weigh the strip of Copper.
-One syringe should be filled with 100cm3 of pure oxygen and the other left empty (if pure oxygen is inappropriate you could use air and base your calculations on the fact that there is 21% oxygen in the air).
-Proceed to pass the oxygen/air from one syringe, across the hot Copper, to the other syringe.
-Continue passing the oxygen/air from side to side over the Copper until the volume of the air/oxygen no longer decreases.
-Wait for the apparatus to cool and weigh the piece of Copper (now Copper Oxide).
· I believe this experiment would prove more accurate and easier to do.
· For the third experiment one could use Copper turnings as an alternative to Copper powder, because the turnings will hopefully not solidify. Another possibility is heating the Copper powder/turnings in a large, more flat crucible therefore increasing the surface area of the Copper.
· To improve the experiment on a whole one could use more samples of differently prepared Copper Oxide.
Evidence:
· From the evidence I have obtained I think it is almost safe to say that the formula of Copper Oxide remains the same regardless of how it is prepared. But this practical did not prove this point too well as only 66% agrees with this conclusion, so the result is almost fifty-fifty.
Further Work:
· Different metals could be used in place of Copper, such as Magnesium or Zinc. This would then discover if there were a possible theory of metal oxides and there formula overall.