Uploaded September 2016 | Updated September 2026, 1 week ago
Potassium Ferrocyanide (nearly transparent yellow solution in the beaker) reacts with a dilute yellow Iron(III)Chloride solution to form the intensively blue colored Prussian Blue.
The color derives from a strong Intervalent Charge-Transfer transition. As d-d-Transitions are forbidden by Quantum Mechanics most complexes appear to be only weakly colored. Charge-Transfer are usually allowed transitions rendering them extremly intense in color.
Potassium Ferrocyanide (nearly transparent yellow solution in the beaker) reacts with a dilute yellow Iron(III)Chloride solution to form the intensively blue colored Prussian Blue.
The color derives from a strong Intervalent Charge-Transfer transition. As d-d-Transitions are forbidden by Quantum Mechanics most complexes appear to be only weakly colored. Charge-Transfer are usually allowed transitions rendering them extremly intense in color.
![Copper Chemistry: Cu(II)/As(III) chameleon [no sound, 2x speed]](https://i.ytimg.com/vi/xHic2pew9bI/mqdefault.jpg "Copper Chemistry: Cu(II)/As(III) chameleon [no sound, 2x speed]
In this video, we show another way to make a beautiful spectrum of colors using Copper chemistry. The reaction is the following: Arsenic(III) is oxidized to Arsenic(V), while Copper(II) is reduced to Copper(I), all happening at a high pH value. But of course, we cannot just add cations and so different precipitates form and dissolve in this process creating many different colors.
We start off with a CuSO4 solution, which is light blue. To this, we add some NaAsO2. We already showed you Copperarsenite in another video. The blue-green precipitate also leaves a greenish aqueous layer on top. When we add KOH the remaining CuSO4 forms the dark blue Cu(OH)2. You can see the surface of the KOH turn dark blue. There is also an equilibrium between Arsenite and
Hydroxide and so the overall color turns more blueish in this process. Now the actual reaction also requires some heat. The KOH dissolving in so little water already causes it to become quite hot. This is why you suddenly see red-brown spots appearing everywhere. When we finally heat it all the Cu(II) is reduced to Cu(I) forming Cu2O.
Much like with our silver video, this is another case where some redox-reactions are just much easier accessible when high pH values are used.
For Arsenic(III to V) the potentials are 0,56 and -0,71 for pH=0 and 14 and for Copper(II to I) the potentials are 0,159 and -0,08.
To reduce Copper(II) to Copper(I) the redox potential of the reducing agent, here Arsenic(III) needs to be lower, which is only fulfilled at higher pH values.")
![Sulfur Chemistry: [Fe(CN)5NOS] from Sodium Polysulfide](https://i.ytimg.com/vi/xm7IYOrwQfA/mqdefault.jpg "Sulfur Chemistry: [Fe(CN)5NOS] from Sodium Polysulfide
There is an interesting reagent called Sodium Nitroprusside. It is sometimes used to identify several ions and is capable of distinguishing between Sulfite and Sulfide for example as well as forming many colored complexes. As we showed in our Cadmium Sulfide video, Sodium Polysulfide, made from elemental Sulfur and Sodium Hydroxide seems to be an alternative for the rather unstable Sodium Sulfide. So we tried to make the famous Sulfide test using Nitroprusside and a selfmade Polysulfide solution.
Here is the result. Note, as we didnt have any other source of H2S or Sulfide we could not compare this to the real test. So we assume the compound formed should have the composition as given in the title.")
