Zinc occurs in nutrient solutions mainly as zinc ion (Zn²⁺) .
There are different methods for determining zinc:
- Atomic absorption spectroscopy (AAS): High-precision determination of zinc.
- Complexometric titration with EDTA: formation of a stable Zn-EDTA complex.
- Spectrophotometry with dithizone: color development by complex formation.
Detailed titration of zinc with EDTA
1. Principle of the method
Zinc ions (Zn²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable complex:
The endpoint of the titration is detected using the Eriochrome Black-T (ErioT) indicator . The color changes from wine red to blue .
2. Chemicals
- 0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
- Buffer solution (pH 10, NH₃/NH₄⁺ buffer)
- Eriochrome Black-T (indicator)
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 buffer solution (pH 10).
- Add 2-3 drops of Eriochrome Black-T indicator.
- Titrate with 0.01 mol/L EDTA until the color changes from wine red to blue.
5. Calculation of zinc concentration
The concentration of Zn is calculated using the formula:
6. Example calculation:
- EDTA concentration: 0.01 mol/L
- Consumed volume: 8.5 mL (0.0085 L)
- Sample volume: 50 mL (0.050 L)
Conclusion
Complexometric titration with EDTA is a precise method for the quantitative determination of zinc in nutrient solutions.
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