A few months back I designed and carried out an experiment to measure the rate of the reaction between ferric chloride and copper.The dependent variable was the rate of the reaction; the independent variable was the the concentration of ferric chloride.
I searched up the reaction and got it from chemiday. There, it stated it as the following:
$$\ce{2FeCl3 + Cu -> 2FeCl2 + CuCl2}$$
So the method I used to measure the rate of this reaction was to use a spectrometer to find a rising absorbance peak for one of the reactants, which I selected to be: $\ce{CuCl2}$.
Then I got some anhydrous $\ce{CuCl2}$ and made a standard curve (Absorbance vs Concentration) for it, so that I could use that to convert the absorbance at it's $\lambda_\mathrm{max}$ to a concentration value.
I carried out the experiment taking the readings at that $\lambda_\mathrm{max}$ at set time intervals, and I reached the conclusion that the relationship between the concentration of ferric chloride and the rate of the reaction between it and copper was a linear one, at least for the concentrations I tested ($\pu{0.1 .. 0.6 M}$).
But now I'm doing more reading to write my report and I found out that this was a complex reaction, meaning that there were several steps to the reaction. After searching up some papers, the consensus seems to be:
\begin{align} \ce{FeCl3 + Cu &-> FeCl2 + CuCl}\tag{1}\\ \ce{FeCl3 + CuCl &-> FeCl2 + CuCl2}\tag{2}\\ \ce{CuCl2 + Cu &-> 2CuCl}\tag{3} \end{align}
As seen from above, it isn't as simple as the original single reaction that I mentioned earlier. First, $\ce{CuCl}$ is produced, then it becomes a reactant in the second reaction to produce $\ce{CuCl2}$, and lastly $\ce{CuCl2}$ becomes a reactant to produce $\ce{CuCl}$.
I'm seriously questioning my method after finding out that a series of reactions takes place, not a just single one. Although the data that I got and the conclusion that I reached matched nicely with other papers that I've read, I'm not sure if the explanation behing my method is correct.
Any input would be greatly appreciated. Thank you.