[woelen]

Hello,

This is my first post to chemicalforums.

I'm a hobby chemist, and one experiment really puzzles me. I dissolved some titanium metal in hydrochloric acid and that gives a blue/purple titanium (III) solution. This dissolving of titanium metal is very slow, even in conc. HCl.

In order to speed up the process I tried dissolving the metal in a solution, containing some HF. I read that with some HF in the solution the metal dissolves much faster. Indeed, the metal dissolves MUCH faster, even with only 10% HCl.
However, to my surprise, a green liquid is obtained instead of a purple liquid and that was NOT mentioned in the text on dissolving titanium metal. On partial oxidation of this green compound, a brown compound is formed (I think it is a mixed valence titanium III/IV complex). On complete oxidation a colorless solution is obtained, most likely a colorless titanium (IV) complex.

I googled around quite a lot, trying to find more info on this reaction. The only thing I could find is mention of a very stable titanium (IV) complex, TiF6(2-), which however is colorless.

The complete experiment and questions are given at the URL below.

http://www.woelen.nl/chem/Ti+F/Ti+F.htm

I already posted the same question to google groups sci.chem and I had a lot of replies, but not an answer to my question.

I ask this question here, just out of curiousity.

If anyone has a clue, I would be pleased to read about that.

Afterwards I did another experiment. I prepared a blue solution of titanium (III) with 30% HCl and some titanium metal. I diluted this blue solution and then I added a small amount of NaF. After adding the NaF, the purple liquid quickly turns light green. On adding a small amount of Na2S2O8, the liquid becomes brown and with shaking it becomes colorless.

Thanks.


PS1: If you want to repeat the experiment, please be careful. I only used small amounts of NaF in 10% HCl, because HF is REALLY nasty. When dilute HCl is used with small amounts of NaF, then hardly any HF is released from the liquid.

PS2: The chemicals used are of good quality. HCl is reagent grade and the titanium metal is of purity 99.9+ %.

[Garneck]

Wild guess: titanium forms a purple complex with chloride ions and a green complex with fluoride ions?

[woelen]

Wild guess: titanium forms a purple complex with chloride ions and a green complex with fluoride ions?

The blue/purple color is known to be due to [Ti(H₂O)₆]³⁺.
The green color probably will be a complex with fluoride ions, but which complex? There might also be chloride ions involved in the complex. And what about the brown color? The brown color most likely is a mixed valence complex, containing Ti(III), Ti(IV), F(-I) and maybe Cl(-I), but this is just my educated guess.

[woelen]

[Ti(H₂O)₆]³⁺.

Wow, the formula layout system is running wild with formulas containing []. I meant [Ti(H2O)6](3+).

[Borek]

I already posted the same question to google groups sci.chem and I had a lot of replies, but not an answer to my question.

I was sure I have seen it before

Welcome aboard!