[Radu]

 Hello! a sample solution containing fluoride was neutralized with methyl red, solid NaCl was added to saturation, and the solution was heated to 70–80°C. The titration was performed with 0.15 M AlCl3 until yellow color of the indicator turned pink. 
   What happened at the end of the titration? ( why did the color of the solution turn into pink?) .  Why was there a need to heat the mixture? I thought that the complex AlF₆^3- is white, and combined with the red color of the indicator( which had, meanwhile, turned from yellow into red) gives a pink color. Is that correct? Anyway, I don't actually understand why the indicator would change its color, given that adding AlCl₃ doesn't change the acidity very much, it only complexes the fluoride, which is a rather strong base in solution. I don't know how the pH gets to become acidic.
   

[Borek]

http://www.chemicalforums.com/index.php?topic=66351.0

[Radu]

 Thanks a lot!