It is to be expected that there will be a loss in weight at the end of the experiment.
SAFTEY ASSESMENT
METHOD
- An empty porcelain boat was placed into the combustion tube, which was then weighed with the weight recorded.
- A spatula of copper (II) oxide was added to the porcelain boat and was placed back into the tube. This was again re-weighed and the weight was recorded.
- The apparatus was set up as shown below – ensuring that the combustion tube was securely held in the clamp and the delivery tube was secure to the gas tap.
- The gas tap was turned on and left for 30 seconds, and the gas was set alight – adjusting the gas tap to make a small flame.
- The copper (II) oxide was strongly heated until a reaction took place.
- Once the reaction had finished, then Bunsen burner was turned off – letting the gas flow through the tube until it had thoroughly cooled down.
- The gas was then turned off and the tube was reweighed and the results were recorded.
SET UP OF EXPERIMENT
RESULTS
Copper (II) oxide – 100.42g – 99.56g = 86g
Copper – 100.22g – 99.56g = 66g
Loss of weight – 86g – 66g = 20g (mass of oxygen)
Mass of copper x 100
Mass of copper (II) oxide
66 x 100 = 76.74 77% of copper in copper (II) oxide
86
INTERPRETATION
The results show that there is a loss in weight in the copper when heated. This is proving that the hypothesis stated at the beginning is therefore correct, with a loss gained. A 77% of copper (II) oxide remained in the porcelain boat. The relative mass of copper (Cu) is 63.5, whereas the relative mass for oxygen (O) is 16. By using the following calculations, it shows the ratio for the number of moles to each element.
Cu mass – Cu relative mass = Number of moles 66 – 63.5 = 1.35
O mass – O relative mass = Number of moles 20 – 16 = 1.25
Cu: O = 1.35:1.25
The number of moles in the overall copper of copper (II) oxide has a slightly larger volume of copper substance than oxygen. (). It is therefore possible to state that the formula for copper (II) oxide is CuO.
EVALUATION
If the experiment were to be repeated again I would weigh and burn several times again at the end of the experiment. By checking the weight and re-burning you can see if more copper oxide is released – giving a more accurate result. Also by using a larger amount of copper (II) oxide, you get a larger result, which means a smaller percentage chance of error. Another change that I would make to the experiment is to ensure that there are no gas leaks from the tubing of the Bunsen burner. By coating the outside with Vaseline, it will give a secure seal. It’s important to keep the gas running through the tube, to prevent the copper oxidizing. By keeping scales close to the experiment set up it would reduce the chance of any further oxidisation occurring. With many of the previous limitations within this experiment, with more practises, it is possible to gain an accurate result for the percentage of copper in copper (II) oxide.
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