Titanium trichloride solution

The 15% titanium trichloride solution was purchased from Carlo Erba... 

The procedure for tellurium is similar to that used for the previous elements except that there is no time delay in the preliminary reduction step, the collection time is 15 sec, and only 6 ml of titanium trichloride solution is used to optimize the determination. 

Titanium trichloride is an extremely easily oxidized material which dissolves in water to form a violet solution. On oxidation, it is converted to the colorless titanic acid, Ti(OH)4. Using a titanium trichloride solution of known strength, it is possible to reduce quantitatively dyes of various classes, the endpoint being taken as the point where the color of the dye disappears. 

Methylene Green (mol. wt. 364.6). Methylene Green is a nitro methylene blue and its reduction requires 6 equivalents of iron. Therefore,. cc. titanium trichloride solution is equivalent to ... 

As the ferrous salt, Knecht used iron ammonium sulfate (Mohr salt) and oxidized this to ferric sulfate with 0.02 N potassium permanganate in sulfuric acid solution. The resulting ferric salt was then back-titrated with titanium trichloride solution. The other, equally simple method consists in dissolving pure iron wire in pure hydrochloric acid and oxidizing the ferrous chloride solution with a few drops of bromine. The excess bromine is removed by boiling and the solution is titrated with the titanium trichloride solution. 

The commercial titanium trichloride solution (about 15 per cent) is diluted by mixing 100 cc. with 100 cc. pure 30 per cent hydrochloric acid. The mixture is heated to boiling and then made up to 1 liter at 18°C. This solution can be held unchanged by storing under carbon dioxide or hydrogen, but it should be restandardized at regular intervals. 

To standardize the solution with iron, an iron solution containing exactly 2 grams of iron per liter is used. This solution should contain 5 per cent hydrochloric acid or sulfuric acid. As an example, it is foimd that 6.85 cc. of a titanium trichloride solution corresponds to 25 cc. of the iron chloride solution, using potassium thiocyanate as the indicator (spot test). Since the iron solution contains 2 grams of iron per liter, 1 cc. TiCls solution corresponds to 0.05/6.85 or 0.007299 grams of iron. 

One mole of methylene blue (mol. wt. 319.6) requires two equivalents of iron (112 grams) for reduction, and therefore 1 cc. titanium trichloride solution corresponds to ... 

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