Determinação Colorimétrica de Fosfato

Medição dos níveis de fosfato na água usando o método do azul de molibdênio

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

Objetivo

Determinar a concentração de fosfato em uma amostra de água usando o método colorimétrico do molibdato de amônio.

Contexto

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.

Avisos de segurança

  • 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 necessário

goggles gloves lab_coat

Materiais

  • 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)

Equipamentos

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

Procedimento

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

Resultados esperados

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.

Limpeza

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

Detalhes

Categoria
Colorimetry
Dificuldade
Advanced (University)
Duração
90 min
Custo estimado
$15,00
Passos
7
Materiais
6

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Frequently Asked Questions

What is the objective of Determinação Colorimétrica de Fosfato?
Determinar a concentração de fosfato em uma amostra de água usando o método colorimétrico do molibdato de amônio.
How difficult is Determinação Colorimétrica de Fosfato?
This experiment is rated as Advanced (University). It takes approximately 90 minutes to complete.
What safety precautions are needed for Determinação Colorimétrica de Fosfato?
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 Determinação Colorimétrica de Fosfato?
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 Determinação Colorimétrica de Fosfato?
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.