So I'm designing an experiment for measuring how the reaction time of copper and ferric chloride is dependent on temperature; here's the reaction:

$$ \ce{FeCl3 + Cu -> FeCl2 + CuCl} $$

The problem I have right now is how to quantitatively measure when the reaction has ended. I know you can visually see when a small copper rod has completely dissolved, but I wanted there to be a quantitative aspect to it rather than qualitative.

I've thought of using a pH probe to see if the PH changes after the reaction takes places and stays static, which I could leverage as an endpoint of the reaction, but the pH probes my school are damaged, I think, since the reading keeps jumping around by about 3 or 4.

If you have measured reaction time in general before, I'd love to hear how you did it.

  • $\begingroup$ You'd probably want to determine the order of your reaction; further calculations down the line, then, are a cakewalk. $\endgroup$ May 19, 2017 at 16:39
  • $\begingroup$ UV-vis would make this very simple, you just need to monitor when the absorbance at a certain wavelength (probably that of Fe(III)?) stops changing. $\endgroup$ May 19, 2017 at 17:18
  • $\begingroup$ I will definitely look into the order of the reaction. $\endgroup$ May 19, 2017 at 21:01

1 Answer 1


Option 1: Spectrometry

Easiest method, in most cases accurate enough. If you know that there are no side-reactions, this is a safe bet. Simply measure some characteristic wavelength for one reactant (preferably $\ce{Fe^{3+}}$) and one product (I would go for the $\ce{Cu^{+}}$ there) and then make measurements of your reaction mixture on the fly.

Option 2: Titration

Not that recommendable if you need any reliable results, but if you are low on budget and/or want a didactic effect. Take a little sample from a big flask and do a $\ce{Fe^{2+/3+}}$-redox-titration.

Option 3: Electrolysis

Don't know how to implement that, but basically you would take the sample and measure the amount of electricity needed to convert all $\ce{Fe^{2+}}$ in that sample back to $\ce{Fe^{3+}}$. Probably more accurate than spectrometry as the measurements of currents can be done quite precisely

You could also do some weird stuff like quantitative chlorine-NMR, but I can not think of any benefit that you would have with that.

  • $\begingroup$ Possibly relevant reading: (faculty.sites.uci.edu/chem1l/files/2013/11/…) $\endgroup$ May 19, 2017 at 20:18
  • $\begingroup$ I think I will go with the Spectrometer method. My school has one of those, so that will be possible. Looks like I have a potential solution; thanks so much for your input! $\endgroup$ May 19, 2017 at 21:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.