Uploaded April 2017 | Updated September 2026, 1 week ago
1) Yellow Product with hot KCN
2) (at the end) grey-blue product with cold KCN
In this video we try to make a Hexacyanochromate(III). Many metals form Hexacyanometallates with Cyanide like Iron as Ferri- and Ferrocyanide. However, not all of them do that as readily as iron does.
For Chromium(III) many people have problems in making decent amounts of this compound. The problem is that it is temperature depended. We try to show this as we do the same experiment twice.
To a boiling solution of KCN a few drops of a blue Cr(III)-Sulfate solution are added. The colour changes to a yellow while a green solid is precipitated.
The same thing is done with cold KCN, here a grey mass forms.
Whenever we do chemistry with Cyanides, not for YouTube usually, we use a slightly acidified solution. Of course, this produces HCN as well but it avoids Hydroxides being formed. Not all elements form Cyanides if dropped into a KCN solution. Some will also hydrolyse fast to form Hydroxides, Oxides and other stuff and liberate HCN. In addition, for the d-metals it is pretty much the same. Hydroxides are like the other thing that can always form if not the cyanide so they have to be avoided. For Cr(III) Cr2O3, so an aqueous Cr2O3 is the green product that forms via certain Hydroxides. There is no real Cr(CN)3 formed as some might suggest for the grey stuff (for Mn(III) however this would be plausible) but rahter an (hydr)oxide species.
Doing the same thing in boiling solutions produces a lot of the soluble Hexacyanochromate(III).
1) Yellow Product with hot KCN
2) (at the end) grey-blue product with cold KCN
In this video we try to make a Hexacyanochromate(III). Many metals form Hexacyanometallates with Cyanide like Iron as Ferri- and Ferrocyanide. However, not all of them do that as readily as iron does.
For Chromium(III) many people have problems in making decent amounts of this compound. The problem is that it is temperature depended. We try to show this as we do the same experiment twice.
To a boiling solution of KCN a few drops of a blue Cr(III)-Sulfate solution are added. The colour changes to a yellow while a green solid is precipitated.
The same thing is done with cold KCN, here a grey mass forms.
Whenever we do chemistry with Cyanides, not for YouTube usually, we use a slightly acidified solution. Of course, this produces HCN as well but it avoids Hydroxides being formed. Not all elements form Cyanides if dropped into a KCN solution. Some will also hydrolyse fast to form Hydroxides, Oxides and other stuff and liberate HCN. In addition, for the d-metals it is pretty much the same. Hydroxides are like the other thing that can always form if not the cyanide so they have to be avoided. For Cr(III) Cr2O3, so an aqueous Cr2O3 is the green product that forms via certain Hydroxides. There is no real Cr(CN)3 formed as some might suggest for the grey stuff (for Mn(III) however this would be plausible) but rahter an (hydr)oxide species.
Doing the same thing in boiling solutions produces a lot of the soluble Hexacyanochromate(III).
![Mercury Chemistry: Co[Hg(SCN)4]](https://i.ytimg.com/vi/jUqjZziourY/mqdefault.jpg "Mercury Chemistry: Co[Hg(SCN)4]
In this video, we make an interesting compound Co[Hg(SCN)4]. It is prepared by mixing a Hg solution with NH4SCN and adding some CoCl2. The compound does not form right away but after a while, tiny blue parts can be seen all over the solution. They quickly fall to the bottom where after a night bigger flakes had formed as well.
As you can the solution is clear in the end, so all the CoCl2 has reacted to form the insoluble Co[Hg(SCN)4]. As they grow so slowly often bigger crystals can be made.
Now you might say this could also be Co(SCN)x. True, they have a similar color. But we made the Thiocyanatocobaltate(II) about 2-3 years ago and since then left it on the shelf and it never precipitated. While here we have a much lower conc. of Co(II). Hg(SCN)2, on the other hand, is not colored because Hg(II) is a d10-system.")
![Mercury Chemistry: Hg3[AsO3]2 and Hg3[AsO4]2](https://i.ytimg.com/vi/kCN6V7e5-Eo/mqdefault.jpg "Mercury Chemistry: Hg3[AsO3]2 and Hg3[AsO4]2
In this video, we make and compare a Mercury(II)-Arsenite and -Arsenate by mixing HgCl2 with NaAsO2 and NaHAsO4. Now usually we do not make every possible compound just to increase the number of videos but for this, we wanted to test something. The Arsenate is, according to literature yellow, while the Arsenite is colorless, but develops a yellow color which is believed to be due to oxidation. We wanted to test this and made both solutions.
At first, you cannot see any precipitate (right jar = Arsenate) but after a while, and a second addition of more Arsenate you can see a yellow turbid color. For the Arsenite, it happens much fast but the solution turns yellow as well, much as expected. If you compare the two after a while you can see that they have the same type of yellow in their solution. 24h later the Arsenate had precipitated as yellow compound while the Arsenite formed a colorless one.
This proves, that the compounds differ in color and only a small fraction, the parts in solution are yellow, probably due to oxygen in the water and the stirring process and that it probably is some oxidation of the Arsenite.
We also tested both up to 350°C for thermochromism but nothing happened.")
