[Olshia]

I have a problem (well not really, but I could call it an issue ) I remember my 5th grade chem teacher showed us a colour-changing experiment involving sodium potassium tartrate & some sort of a catalyst. The reaction went from bluish green to pink & then reversed, or something like that  (can't reckon the exact colour change, but I know it reversed & came back to the original colour). It also had some gas produced, I am almost sure it was very bubbly/foamy.

Does anyone know what other chemicals are involved? I would also be grateful for some sort of explanation of what's actually going on, because my chem teacher just told us it was her fav experiment showing the catalyst's action, as it went through the reaction & the catalyst was recovered (she said that was why it came back to the original state).

May I use your help here?
Thanks a lot!

[gregdwulet]

Seems to me that the reaction you're talking about is that of sodium potassium tartrate (KNaC₄H₄O₆·4H₂O) with hydrogen peroxide (H₂O₂) and cobalt (II) chloride (CoCl₂).

This reaction uses the H₂O₂ to oxidize the tartrate ion to produce carbon dioxide gas (CO₂) and methanoate ions.

The color change occurs when the CoCl₂, which I believe is aqueous and has a pink color when in solution, is oxidized to form Co⁺³ ions, which are green. The catalyst was recovered because these Co⁺³ ions are reduced back to Co⁺² (pink) when the reaction completes. The color change should have been pink-green-pink.

The gas produced is, obviously, CO₂.