An experiment to find the empirical formula when copper reacts with iodine
This experiment has been carried out to find out the empirical formula of the following reaction.
Copper + Iodine → Copper Iodide
It is important to find out the mass of the copper and iodine both before and after the experiment, so that the empirical formula can be calculated.
A length of copper strip was cleaned using emery paper, then wiped with dry filter paper. After, the copper strip was weighed. Approximately 0.3g of iodine crystals was weighed and then placed in to a dry boiling tube. The copper strip was then placed into the boiling tube, two centimetres above the iodine, and bent over the edge to place it in a secure position.
The boiling tube was then heated over a Bunsen (tongs were used to hold the boiling tube). Soon, vapour could be seen. At the moment the vapour was seen, the boiling tube was removed from the heat until the vapour was no longer visible. Once no more vapour could be seen, the boiling tube was placed over the Bunsen again. This process was repeated until no more iodine crystals remained.
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The boiling tube was then allowed to cool, and the copper strip was removed and weighed. After weighing, the yellow coating of copper iodide was scrapped off the copper strip, into a watch glass and then weighed. Using the results regarding the weight of the copper strip before and after the experiment and the weight of the iodine, the empirical formula could be calculated.
Using the empirical formula, the following chemical equation can be used to show the product when copper and iodine are heated.
Cu + I CuI
It is not clear whether this is correct or not as only one set of data has been used to calculate this empirical formula. In order to check whether this is the correct formula, the experiment would need to be repeated and an average taken and used to calculate the empirical formula.
Although the results obtained from this experiment has allowed the empirical formula to be calculated, the weight of the iodine and copper will have a degree of inaccuracy due to the equipment used. This inaccuracy can be expressed as a precision (or absolute) error. The copper and iodine were weighed of an electronic balance that shows the weight to two decimal places. This means that for all the weights given by the scales, the actual weight is ± 0.005 (g) of the value shown.
In order to show what the precision error of different measurements means, they are normally expressed as a percentage using the following formula.
Percentage error = (error x 100) ÷ reading
The percentage errors of the results above are shown in the table below.
The percentage error shows that the greater the original reading, the smaller the percentage error is. Therefore, it can be concluded that, should this experiment be performed again, a larger amount of each substance should be used in order for the results to be as accurate as possible.
Errors in the data could have also been caused when the experiment was carried out. For example, there was no guarantee that the copper strip was cleaned completely with the emery paper. Also, the copper strip may have reacted with oxygen to form copper oxide, which will disable the iodine from reacting with all of the copper. Another stage in the procedure which could have led to incorrect data is the removal of the yellow copper iodide, as it is not certain whether every copper iodide particle was removed. Also, while heating the boiling tube, with iodine and copper present, some of the vapour may have escaped before the boiling tube was removed from the flame of the Bunsen.
If this experiment was to be carried out again, the mass of both the iodine and copper should be weighed on a balance which provides mass to a greater degree of detail. This will mean that the results will be more concise and accurate as the percentage error will be lower.
Akash Askoolum (S10)