Science Buddies: "Ask an Expert"

Hello,

I conducted an experiment very similar to the "magic of photochemistry experiment" on this website (https://www.sciencebuddies.org/science- ... ochemistry). I followed the authors note and performed the experiment without the oxalic acid and measured the colour change by comparing different absorbance values using a spectrometer. I have run into a couple of problems and I was wondering if anyone could provide me with some guidance to help me finish my lab report. My first question is I was getting stuck with what the reaction actually is? I used ammonia (household) which is ammonium hydroxide and iodine solution (iodine, potassium iodide, and water) when they were mixed I created the dark colour and was wondering what that product is? Is it nitrogen triiodide? Is it iodide ions on their own? Additionally, I was wondering if anyone could explain to me why the solution goes clear? Is it because of p and d blocks are generally colourless? But I would get confused on that thought because then why is the iodine solution a dark colour?
I hope these questions make a little sense.
I would greatly appreciate any feedback and guidance. Thanks so much.
Meah

Hello dlkmod,

By "iodine solution" (with iodine, potassium iodide, and water), are you referring to Lugol's iodine/potassium triiodide (see https://en.wikipedia.org/wiki/Lugol%27s_iodine)? It also consists of water, potassium iodide, and iodine. If that is what you used, its molecular formula is I3K. As you only described mixing ammonium hydroxide (NH4OH) with the iodine solution, I believe your reactants would be NH4OH + I3K. This may help you make some progress. However, I am not positive as to what the product of the reaction is; someone more experienced than I am may be able to help you with determining that.

The dark-colored product you obtained by mixing the iodide solution and ammonium hydroxide was most likely not iodide ions; this is due to the fact that iodide ions are colorless. As for the solution becoming clear, please explain what you changed before this happened so that we have something to work with.

I hope that this post proves helpful; please feel free to respond if you have any more comments or questions.

cvionis

Hello cvionis,

Thank you for the response.
I do believe that the iodine solution is Lugol's (here is the SDS https://boreal.com/assetsvc/asset/en_CA ... 2/contents ). My procedure for the reaction was mixing the ammonia and iodine then put it into 5 test tubes exposed to different light sources. At 15 minute intervals, I put the solutions into a spectrometer to measure how the absorbance values have changed. The reaction was going from dark to clear. I think my products would be ammonium iodide and potassium hydroxide because both would make a clearish solution (is that correct?).
I was thinking the reaction would be NH4OH + KI yields NH4I + KOH
does that seem correct?
I did not add anything else to the reactants it was only light and time that changed the colour

Thanks,

Hi dlkmod,

Thank you for the clarification. I looked into this chemical equation (NH4OH + KI → NH4I + KOH) further, and ultimately it does appear that it would be correct; especially since both of its products are colorless.

Please let me know if you have any more comments or questions.

cvionis