Potassium, quantitative analysis

Quantitative Analyse von Kalium

Potassium occurs in nutrient solutions as free potassium ion (K⁺).

There are different methods for determining potassium:

  • Flame photometry: Measurement of the emission of K⁺ ions.
  • Ion-selective electrodes: direct measurement of potassium concentration.
  • Gravimetric precipitation: Precipitation as potassium tetraphenylborate (K[B(C₆H₅)₄]).
  • Titration with sodium tetraphenylborate (Na[B(C₆H₅)₄]): Precise determination of K⁺.

Detailed titration of potassium with sodium tetraphenylborate

1. Principle of the method

Potassium ions (K⁺) react with sodium tetraphenylborate (Na[B(C₆H₅)₄]) to form sparingly soluble potassium tetraphenylborate:

K⁺ + Na [B(C₆H₅)₄] → K[B(C₆H₅)₄] ↓ + Na⁺

The endpoint of the titration is detected by turbidity measurement (nephelometry) or visually.

2. Chemicals

  • 0.01 mol/L sodium tetraphenylborate solution (Na[B(C₆H₅)₄])
  • Buffer solution (pH = 7)
  • Indicator: Toluene extract (optional for turbidity determination)

3. Experimental setup

Required equipment:

  • Burette (25 mL, division 0.1 mL)
  • Erlenmeyer flask (100 mL)
  • Pipette (10 mL)
  • Turbidity meter (optional)

4. Implementation

  1. Pour 10 mL of the nutrient solution into a 100 mL Erlenmeyer flask.
  2. Add 10 mL of buffer solution.
  3. Titrate with 0.01 mol/L Na[B(C₆H₅)₄] until persistent turbidity is observed.

5. Calculating the potassium concentration

The concentration of K⁺ is calculated using the formula:

c ( K⁺ ) = V Na[B(C₆H₅)₄] ⋅ c Na[B(C₆H₅)₄] V Probe

 

6. Example calculation:

  • Sodium tetraphenylborate concentration: 0.01 mol/L
  • Consumed volume: 12.5 mL (0.0125 L)
  • Sample volume: 50 mL (0.050 L)
c ( K⁺ ) = 0.0125 ⋅ 0.01 0.050 = 0.0025 mol/L = 2.5 mmol/L

 

Conclusion

Titration with sodium tetraphenylborate is a precise method for determining potassium in nutrient solutions.

ID: 626

Kontext: 

URL
Parent Category: Technology
Category: Analysis
Also available: German (Hochdeutsch)

Analysis