Some chemistry pictures from a long time forum lurker

Hello!

A bit of background - I've been a home chemist since the early 2010s. I've been aware of this forum's existence around 2012-2013, at the same time I discovered Woelen's website. I don't know why, but I hesitated to create an account here, until now. In an academic sense, I'm more involved with biotechnology (genetic engineering) and molecular biology. This year I recieved my master's degree. But I still enjoy chemistry as a hobby. I do most of my chemistry on a small scale and in aqueous solutions, I don't have the equipment to do things like distillations or syntheses which require prolonged heating and reflux systems (but I do want to invest in a hotplate with stirring this year or next, so that might change).

I've rambled about my self long enough, time to show you the pictures. Woelen has already seen them in emails, but encouraged me to show them to all of you, so here they are:

Ferrate(VI)

I've made some ferrate(VI) with the usual Fe salt + alkali + hypochlorite route. I think it's still nice to look at this more unusual oxidation state of iron, in its beatiful purple color. Here is ferrate(VI) next to samples of Fe(III) and Fe(II):




Vanadium oxidation states (II-V)

A classic experiment, nothing too special. NH₄VO₃ was dissolved in 10% HCl, and then split across 4 test tubes. To one I added sulfite to obtain the blue VO²⁺ and to the next two, Zn powder (with some heating) to get V³⁺ and V²⁺




Chromium(II) in solution and as crystallized solid

I made a very concentrated chrome alum solution in 10% HCl, which I reduced with Zn powder. As the solution went to a beautiful blue color, I secured the top of the test tube with mineral oil, to cut off contact with the air. I then put this in the refrigerator overnight. The next day I was pleased to find that some of the Cr(II) had crystallized out of solution as a blue salt. I used chrome alum and used Zn powder as a reducing agent, so it's likely that this salt was contaminated with other ions. I'd like to revisit this experiment, using CrCl₃ and Cr powder or shavings to hopefully produce pure CrCl₂ hydrate crystals. The black stuff is the leftover Zn powder.






Manganese oxidation states(II-VII)

I consider these one of my best photos yet. I wanted to create a side-by-side comparison of all the oxidation states of manganese which can be created in a home lab without exotic chemicals or specialized equipment.
The starting materials were KMnO₄ and MnSO₄. For Mn(VI) I heated dilute KMnO₄ in 5 M KOH. Mn(IV) was created as MnO₂ by reducing permanganate with sucrose. Mn(III) was obtained by oxidizing Mn²⁺ with BrO₃^- in H₂SO₄. Mn(V) was a challenge. I initially tried obtaining the hypomanganate by trying the first two methods described in the potassium hypomanganate wikipedia page. I used ~10 M KOH in both attempts, but these didn't work for me. I then discovered Bedlasky's thread about obtaining hypomanganate with thiosulfate. This proved successful, so thank you very much Bedlasky for saving this experiment and allowing me to snap these neat photos:






Belousov-Zhabotinsky experiments

I did the BZ experiment in two variants - one with the classic blue/red oscillation (ferroin), the other with the often described but almost never seen green/blue/red oscillations (ferroin + cerium).














These photos were done in poor lighting so perhaps they're not the greatest. I'd love to do it again in a bigger petri dish with better lighting and make a timelapse video of the ferroin + cerium variant, because seemingly nowhere can you find a video of these oscillating tricolored waves. Also, if any of you know recipies for adding even more or different colors to the BZ reaction, I'd love to hear about them.


That would be all I have for now, but perhaps I'll collect some more photos to share. Cheers!

[Edited on 28-9-2020 by EthidiumBromide]

Quote: Originally posted by EthidiumBromide

Hello! I'd like to revisit this experiment, using CrCl3 and Cr powder or shavings to hopefully produce pure CrCl2 hydrate crystals.

Quote: Originally posted by EthidiumBromide

Mn(V) was a challenge. I initially tried obtaining the hypomanganate by trying the first two methods described in the potassium hypomanganate wikipedia page. I used ~10 M KOH in both attempts, but these didn't work for me. I then discovered Bedlasky's thread about obtaining hypomanganate with thiosulfate. This proved successful, so thank you very much Bedlasky for saving this experiment and allowing me to snap these neat photos:

You are welcome . You have really nice clean solution! I sometimes had cloudy solution because of Na2CO3 contamination or because of NaOH started to crystallize out after cooling.

Btw. your Mn3+ solution is quite interesting! I never heard, that bromate can oxidize Mn(II) to Mn(III), before! I few times prepare some Mn(III) complexes, which are stable in aqueous solution - complexes with EDTA, phosphate and pyrophosphate, all are red. Woelen also recently mention reaction between KMnO4/MnO2 and HCl (and also MnCl2 and chlorate/ClO2) - in this reaction green chloride complexes of Mn(III) and Mn(IV) are formed.

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

Purple aqua and sulfato complexes can be made by oxidizing MnSO4 with KMnO4 in conc. sulfuric acid (use just small quantities, KMnO4 form in conc. H2SO4 unstable Mn2O7). Something similar should work in conc. H3PO4 (I don't try it yet, but I read about it).

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

Mn(III) can be also make by oxidizing Mn(II) acetate by KMnO4 in glacial acetic acid.

I read about preparation of K3[Mn(C2O4)3], but it is quite unstable (unlike his Fe analogue).

Quote: Originally posted by EthidiumBromide

I did the BZ experiment in two variants - one with the classic blue/red oscillation (ferroin), the other with the often described but almost never seen green/blue/red oscillations (ferroin + cerium).

Cool!

Have you ever tried Briggs-Rauscher reaction?

Quote: Originally posted by Bedlasky

Btw. your Mn3+ solution is quite interesting! I never heard, that bromate can oxidize Mn(II) to Mn(III), before! I few times prepare some Mn(III) complexes, which are stable in aqueous solution - complexes with EDTA, phosphate and pyrophosphate, all are red.

If the BZ reaction is done with Mn²⁺ catalyst, you get oscillation between Mn(II) and Mn(III). So by this logic, if I take out the bromide and malonic acid for reduction, I should just get simple oxidation of Mn²⁺ to Mn³⁺. I prepared a solution of KBrO₃ in 20% H₂SO₄ (the same I used to prepare the Mn³⁺ earlier), to which I added dropwise a solution of MnSO₄. As you can see, in low concentration Mn³⁺ has a salmon color, but as it gets more concentrated, it shifts to a red-amaranth (it doesn't show well on the pictures, but it has a slightly more purple tint in person).










Mn³⁺ isn't very stable in this form, it needs very acidic enviroment. If the acid solution isn't concentrated enough, Mn(III) quickly disproportionates to Mn(IV) and Mn(II). A similar result occurs if you dilute the concentrated Mn³⁺ with pure water, no acid added, as I did here - I took a few drops of the concentrated Mn(III) and added some distilled water.



Though even in concentrated acid, the color of solution shifts to a more brownish red color after a day of storage at room temp, indicating that it's not very stable, unless complexed, as you've mentioned.

Quote: Originally posted by Bedlasky

Have you ever tried Briggs-Rauscher reaction?

Yes, I have done it a few times, but I don't have yet a magnetic stirrer, so I had to mix the reaction myself, by swirling the flask. It still worked, oscillating between colorless, amber and dark blue.

Quote: Originally posted by EthidiumBromide

as some MnO2 had formed that made it opaque and obscured the blue color. [Edited on 28-9-2020 by EthidiumBromide]

Quote: Originally posted by EthidiumBromide

Perhaps my thiosulfate is not the best quality? It is quite old, so maybe some impurities caused some of the hypomanganate to decompose? I'll be ordering fresh thiosulfate soon as I'm almost out anyway.

Thts ann interesting B-Z reaction. I have only seen the blue/red oscillation but never the green/red/blue ones.