Titanium occurs in nutrient solutions primarily as the titanium(IV) ion (TiO₂⁺) or as a titanyl complex (TiO²⁺) . It may be essential, but traces of Ti 3+ are so ubiquitous that its addition is rarely justified. At 5 ppm, beneficial growth effects are quite remarkable in some crops, e.g., pineapple and peas. A variable micronutrient.
There are various methods for determining titanium:
- Spectrophotometry with peroxo complexes: formation of a yellow titanyl peroxide complex.
- Gravimetric determination: precipitation as titanium dioxide (TiO₂) and weighing.
- Redox titration with iron(II) sulfate: reduction of Ti(IV) to Ti(III) and back titration.
Detailed redox titration of titanium with iron(II) sulfate
1. Principle of the method
Titanium(IV) is reduced with iron(II) sulfate (Fe²⁺) :
The back titration is carried out with potassium permanganate (KMnO₄) in sulfuric acid solution, resulting in a violet endpoint.
2. Chemicals
- 0.01 mol/L iron(II) sulfate (FeSO₄) solution
- 0.01 mol/L potassium permanganate (KMnO₄) solution
- Sulfuric acid (H₂SO₄, 1 mol/L)
3. Experimental setup
Required equipment:
- Burette (25 mL, division 0.1 mL)
- Erlenmeyer flask (250 mL)
- Pipette (10 mL)
- Magnetic stirrer
4. Implementation
- Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
- Add 10 mL of iron(II) sulfate solution and reduce in a hot water bath (60°C) for 5 minutes.
- Titrate excess Fe²⁺ with 0.01 mol/L KMnO₄ until a violet color remains stable .
5. Calculation of titanium concentration
The concentration of Ti is calculated using the formula:
6. Example calculation:
- KMnO₄ concentration: 0.01 mol/L
- Consumed volume: 7.6 mL (0.0076 L)
- Sample volume: 50 mL (0.050 L)
Conclusion
Redox titration with iron(II) sulfate and back titration with potassium permanganate is a precise method for the quantitative determination of titanium in nutrient solutions.
