Dosage Colorimétrique du Phosphate

Mesure des niveaux de phosphate dans l'eau par la méthode du bleu de molybdène

Colorimetry Advanced (University) 90 min ~$15,00

Objectif

Déterminer la concentration en phosphate d'un échantillon d'eau par la méthode colorimétrique au molybdate d'ammonium.

Contexte

The molybdenum blue method is the standard technique for phosphate determination in environmental water analysis. Phosphate ions react with ammonium molybdate in acidic solution to form a phosphomolybdate complex, which is then reduced by ascorbic acid to form an intensely blue colored complex (molybdenum blue). The intensity of the blue color is proportional to phosphate concentration. This method can detect phosphate at concentrations as low as 0.01 mg/L.

Avertissements de sécurité

  • Ammonium molybdate solution contains sulfuric acid — corrosive
  • Antimony compounds are toxic
  • Use pipette fillers — never mouth-pipette
  • Dispose of molybdate waste in heavy metal waste container

EPI requis

goggles gloves lab_coat

Matériaux

  • Potassium dihydrogen phosphate (KH₂PO₄) (1 g)
    For stock standard
  • Ammonium molybdate solution (100 mL)
    2.5% in 5M H₂SO₄
  • Ascorbic acid solution (50 mL)
    1% freshly prepared
  • Antimony potassium tartrate (10 mL)
    Catalyst solution
  • Environmental water sample (100 mL)
    Pond, river, or tap water
  • Distilled water (500 mL)

Équipement

Spectrophotometer Cuvettes (1 cm path length) Volumetric flasks (50 mL, 8 total) Pipettes (1 mL, 5 mL, 10 mL) Water bath (37°C)

Procédure

1

Prepare a 100 ppm phosphate stock solution by dissolving 0.1433 g KH₂PO₄ in distilled water and making up to 1 L. Then prepare working standards: 0, 0.1, 0.2, 0.5, 1.0, 2.0 ppm.

15 min
2

Prepare the combined reagent: mix 50 mL ammonium molybdate solution, 5 mL antimony potassium tartrate solution, and 30 mL ascorbic acid solution. Use within 4 hours.

10 min Handle acid carefully
3

To each 50 mL standard flask and the water sample, add 8 mL of combined reagent. Mix well.

10 min
4

Allow color development for 10 minutes at room temperature (or 5 minutes in 37°C water bath).

10 min
5

Measure absorbance at 880 nm (or 710 nm if 880 nm is not available). Zero with the blank.

15 min
6

Plot the calibration curve. Determine the phosphate concentration of the water sample.

15 min
7

Evaluate the result against environmental standards. Phosphate above 0.02 mg/L may indicate eutrophication risk.

15 min

Résultats attendus

The calibration curve should be linear in the 0–2 ppm range. The blue color deepens with increasing phosphate. Environmental samples typically show 0.01–0.5 ppm in clean water, higher in agricultural runoff areas.

Nettoyage

Collect all molybdate-containing solutions in labeled waste. Rinse all volumetric glassware. Clean cuvettes immediately.

Détails

Catégorie
Colorimetry
Difficulté
Advanced (University)
Durée
90 min
Coût estimé
$15,00
Étapes
7
Matériaux
6

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Frequently Asked Questions

What is the objective of Dosage Colorimétrique du Phosphate?
Déterminer la concentration en phosphate d'un échantillon d'eau par la méthode colorimétrique au molybdate d'ammonium.
How difficult is Dosage Colorimétrique du Phosphate?
This experiment is rated as Advanced (University). It takes approximately 90 minutes to complete.
What safety precautions are needed for Dosage Colorimétrique du Phosphate?
Key safety precautions include: Ammonium molybdate solution contains sulfuric acid — corrosive; Antimony compounds are toxic; Use pipette fillers — never mouth-pipette.
What materials are needed for Dosage Colorimétrique du Phosphate?
The main materials required are: Potassium dihydrogen phosphate (KH₂PO₄), Ammonium molybdate solution, Ascorbic acid solution, Antimony potassium tartrate, Environmental water sample.
What results should I expect from Dosage Colorimétrique du Phosphate?
The calibration curve should be linear in the 0–2 ppm range. The blue color deepens with increasing phosphate. Environmental samples typically show 0.01–0.5 ppm in clean water, higher in agricultural runoff areas.