[Count of Monte Cristo]

Last weekend, I dissolved approx. 8g of iron in the form of steel wool in hot HCl, once dissolved I filtered to get a clear, lightish green solution of FeCl2 (approx. 125mL). The next step was to reheat for recrystallization, however I didn't have time to do this in the week that followed so I had to wait until the weekend, that is, today. I gently heated the solution down to about 60mL or so until a saw a crystal residue forming on the sides. Now during this boiling process the solution changed color from light green to dark yellow then to an amber-brown color, is this supposed to happen?

The only cause I can think of is an oxidation to FeCl3, but after doing some research the only way I could see this happening is chlorine gas being evolved from excess HCl during heating, and then going back into solution and bonding with the FeCl2. However I don't see this as being very likely.

Below I have some pictures of the solution after heating, in the background of the first one you can see my bunsen burner, this is what I used to evaporate the solution.

[Borek]

Air oxygen is enough.

[Count of Monte Cristo]

So it slowly oxidized over the past week? But then shouldn't I have noticed a color change before I boiled the solution?

[billnotgatez]

@Count of Monte Cristo
Have you done the experiment of
Doing your process and NOT waiting the week to see if you have the same result?

[Borek]

shouldn't I have noticed a color change before I boiled the solution?

To some extent yes, no idea why you have not seen it. As Bill wrote, check if the crystallization made immediately won't give better effect.

Also note most of Fe(II) compounds are not stable in contact with air, they will slowly oxidize.

[Count of Monte Cristo]

Over the past two days I recrystallized and decanted the solution, I have come up with a product that seems about half FeCl₂ and half FeCl₃. What must have happened is only some of the solution oxidized while I left it to sit for a week, but not enough to result in a color change. I will be running two more experiments off of this to try and produce both iron(II) and (III) solutions respectively based on different waiting periods before recrystallization. I would like to thank you all for your help.

[Zyklonb]

Oxygen in air can easily oxidize iron (II) chloride hydrates to Iron (III) chloride hydrates.
The hexahydrate is usually given as the simplified empirical formula FeCl₃⋅6H2O. It should be shown as trans-[Fe(H₂O)₄Cl₂]Cl⋅2H₂O and the systematic name tetraaquadichloroiron(III) chloride dihydrate, which more clearly represents its structure.
From this, you can clearly see that it's the oxygen that oxidizes the iron, not chlorine, so as long as an excess of chloride ion is available in a solution of iron (II) chloride, (III) chloride will form - granted available oxygen or hydrogen peroxide is present.