MidLifeChemist - 30-11-2022 at 07:50
I wanted to share a video that I was part of for ChemTalk.
I haven't had much time to get into the lab for the past year so it was nice to be able to be part of this. My family also was there and they were
quite impressed by the array of colors.
In the video, we show all of the colors of the oxidations states of vanadium, including intermediate colors. We also show red and orange using
potassium permanganate - which means we produce all of the colors of the rainbow in one solution without use of indicators.
To our knowledge, this is the first time someone has demonstrated this procedure using vanadium pentoxide (which is much easier and cheaper to get)
instead of ammonium metavanadate. We also show that you don't need zinc-mercury amalgam to easily reach the +2 oxidation state.
I hope you enjoy the video, there is a link to the procedure in the video description.
https://www.youtube.com/watch?v=6y4pR7KIK8c
j_sum1 - 30-11-2022 at 15:11
Thanks. I enjoyed this.
I did something similar myself a couple of weeks ago. I now have some lovely ampoules showing the four oxidation states. I also started with vanadium pentoxide. Like you, I used a strip of zinc for reduction.
I will do it again some time. But next time I will make solutions of II and V and use these to make solutions of III and IV. I may video it. I
think it would be good from an educational standpoint.
I was not aware of the peroxide complex. It looks very similar to the Ti peroxide complex although it seems darker and less orange in appearance. I
might have to do this as well.
MidLifeChemist - 30-11-2022 at 20:16
"I did something similar myself a couple of weeks ago. "
That's awesome! great minds think alike 
glad to see you also decided to go the
pentoxide route. The ampules looks beautiful, I may have to do it again and make some ampules like that.
How long did it take you to get the purple color of the +2 state? I would think with a zinc strip it may take a while.
j_sum1 - 30-11-2022 at 20:31
I don't actually recall. I was shaking the test tube for some time. I may have had lunch and come back. It was a problem that the reaction would
reverse when the zinc was removed.
I ended up making an additional ampoule with a small amount of zinc still in it. (Not photographed.) The colour stabilised to a beautiful rich purple
by the following day. It's really nice.
DraconicAcid - 30-11-2022 at 20:46
I know I've mentioned using pottery-grade V2O5 for this reaction on this forum somewhere, as well as using the peroxide test. I used aluminum to
reduce it to V(II)- it works very well at one campus, and not at all at the other (which ticks me off every year).
You've done a great video, though.
woelen - 1-12-2022 at 01:43
I also did some nice experiments with vanadium, several years ago:
oxidation states: https://woelen.homescience.net/science/chem/exps/vanadium/in...
peroxo complexes: https://woelen.homescience.net/science/chem/exps/KVO4/index....
MidLifeChemist - 1-12-2022 at 11:11
>> I know I've mentioned using pottery-grade V2O5 for this reaction on this forum somewhere
Yeah, I very well may have got the idea here. This forum and woelen's site are my goto places for transition metal chemistry ideas.
>> You've done a great video, though
thank you!
>> I also did some nice experiments with vanadium, several years ago:
you have so many great experiments on your site, it had given me the idea to try to make some Titanium compounds, including the green colored one with
NaF
Bedlasky - 1-12-2022 at 17:03
Nice experiment! I also did this with V2O5 and zinc powder.
I made some sodium orthovanadate from V2O5, because dissolving V2O5 in NaOH is tedious, it dissolves painfully slowly and it is contaminated with some
black stuff which won't dissolve, you must filter it off. Even in your video you can clearly see that you have some undissolved stuff in the flask.
Sodium orthovanadate dissolve quickly in water producing colorless solution. It is little bit contamianted with carbonate, but it really doesn't
matter to me for these demonstrations.
MidLifeChemist - 5-12-2022 at 08:29
thanks Bedlasky
It's very exciting to hear that you worked on this also.
yeah, when making sodium vanadate, there may have been some undissolved stuff, but the final solutions of V+5,+4,+3,+2 that I poured into the beakers
were very clear - no filtering needed!
how did you make your sodium orthovanadate?
[
rquote=679031&tid=159113&author=Bedlasky]Nice experiment! I also did this with V2O5 and zinc powder.
I made some sodium orthovanadate from V2O5, because dissolving V2O5 in NaOH is tedious, it dissolves painfully slowly and it is contaminated with some
black stuff which won't dissolve, you must filter it off. Even in your video you can clearly see that you have some undissolved stuff in the flask.
Sodium orthovanadate dissolve quickly in water producing colorless solution. It is little bit contamianted with carbonate, but it really doesn't
matter to me for these demonstrations.[/rquote]
Bedlasky - 5-12-2022 at 10:56
Simply by dissolving V2O5 in 10% NaOH, then evaporating water on steam bath. If you need to know how much V(V) is in the solid, you can determined it
by ferrometric titration.
woelen - 5-12-2022 at 23:48
I also made Na3VO4. I made it by dissolving V2O5 in a solution of NaOH (fairly concentrated, maybe 15%) and I added excess V2O5 in small steps. I
continued adding small amounts of V2O5, while gently heating the solution, and I did this until no more V2O5 could be dissolved. This results in a
turbid yellowish liquid (due to the slight excess of V2O5). I let the solid material settle at the bottom in a long/narrow bottle. Just put it aside
for a few days. Next, I decanted the clear liquid (you can also filter, but I preferred decanting, because I did not want any solid matter at all,
also no ultrafine particles). The resulting liquid is absolutely clear and very pale yellow. To this, I added a single granule of NaOH to make it
colorless, and then I let this liquid evaporate in a glass dish at a warm place free of dust. You get a white powdery solid (no nice crystals, just a
powdery crust). I crunched this. It is hard to obtain really pure Na3VO4, I think that my stuff is somewhere between Na3VO4 and NaVO3. It dissolves in
water easily and gives perfectly clear solutions.
I did a similar thing with MoO3 and WO3 to make approximate Na2MoO4 and Na2WO4.