Molybdenum, quantitative analysis

Molybdenum occurs in nutrient solutions mainly as molybdate ion (MoO₄²⁻) .

There are various methods for determining molybdenum:

  • Atomic absorption spectroscopy (AAS): High-precision determination of Mo.
  • Thiocyanate spectrophotometry: formation of a red Mo-thiocyanate complex.
  • Redox titration with iron(II) sulfate: reduction of molybdenum(VI) to molybdenum(III).

Detailed titration of molybdenum with iron(II) sulfate

1. Principle of the method

Molybdate ions (MoO₄²⁻) are reduced in acidic solution with iron(II) sulfate (Fe²⁺):

2MoO42- + 8H⁺ + 6Fe²⁺ → 2Mo³⁺ + 3Fe³⁺ + 4H2O

The end point of the titration is identified by the color change from blue to colorless .

2. Chemicals

  • 0.01 mol/L iron(II) sulfate solution (FeSO₄)
  • 1 mol/L sulfuric acid (H₂SO₄)
  • Distilled water

3. Experimental setup

Required equipment:

  • Burette (25 mL, division 0.1 mL)
  • Erlenmeyer flask (250 mL)
  • Pipette (10 mL)
  • Magnetic stirrer

4. Implementation

  1. Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
  2. Add 10 mL of 1 mol/L sulfuric acid.
  3. Titrate with 0.01 mol/L FeSO₄ until the blue color disappears.

5. Calculation of the molybdenum concentration

The concentration of Mo is calculated using the formula:

c ( Mo ) = V FeSO₄ ⋅ c FeSO₄ ⋅ 2 6 V Probe

6. Example calculation:

  • Iron(II) sulfate concentration: 0.01 mol/L
  • Consumed volume: 6.8 mL (0.0068 L)
  • Sample volume: 50 mL (0.050 L)
c ( Mo ) = 0.0068 ⋅ 0.01 ⋅ 2 6 ⋅ 0.050 = 0.00453 mol/L = 4.53 mmol/L

 

Conclusion

Redox titration with iron(II) sulfate is a very reliable method for the quantitative determination of molybdenum in nutrient solutions.

ID: 635

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Parent Category: Technology
Category: Analysis
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Analysis