Eisenbestimmung in Wasser

Messung der gelösten Eisenkonzentration durch Thiocyanat-Kolorimetrie

Colorimetry Intermediate (High School) 75 Min. ~$10,00

Ziel

Die Konzentration von Eisen(III) in einer Wasserprobe mithilfe der kolorimetrischen Thiocyanatmethode bestimmen.

Hintergrund

Iron(III) ions react with thiocyanate ions (SCN⁻) to form the intensely red-colored complex [Fe(SCN)]²⁺. The intensity of the red color is proportional to the Fe³⁺ concentration, following the Beer-Lambert law. This method is widely used in water quality testing and environmental monitoring. Students learn both the analytical technique and the chemistry of complex ion formation.

Sicherheitswarnungen

  • FeCl₃ solution stains skin and clothing
  • KSCN is harmful if swallowed
  • HNO₃ is corrosive — handle with care
  • Dispose of thiocyanate waste in designated containers

Erforderliche PSA

goggles gloves lab_coat

Materialien

  • Iron(III) chloride (FeCl₃) standard (100 mL)
    0.01 M stock solution
  • Potassium thiocyanate (KSCN) (100 mL)
    0.1 M solution
  • Dilute HNO₃ (0.1 M) (50 mL)
    To maintain acidity
  • Water sample (50 mL)
    Unknown iron content
  • Distilled water (500 mL)
    For dilutions

Ausrüstung

Colorimeter or spectrophotometer Cuvettes (matched pair) Volumetric flasks (50 mL, 7 total) Pipettes (1 mL, 5 mL, 10 mL) Pipette filler

Durchführung

1

Prepare a series of standard Fe³⁺ solutions (0, 1, 2, 4, 6, 8, 10 ppm) by diluting the stock FeCl₃ solution in 50 mL volumetric flasks.

15 Min.
2

Add 5 mL of 0.1 M KSCN and 2 mL of dilute HNO₃ to each standard flask and the water sample. Make up to volume with distilled water.

10 Min.
3

Allow 5 minutes for full color development. The solutions should range from pale to deep red.

5 Min.
4

Set the colorimeter to 480 nm. Zero with the blank solution (0 ppm Fe³⁺ + KSCN).

5 Min.
5

Measure the absorbance of each standard solution and the water sample.

15 Min.
6

Plot the calibration curve (absorbance vs. concentration). Use it to determine the iron concentration in the water sample.

15 Min.
7

Calculate the iron concentration and evaluate whether the water meets drinking water standards (<0.3 ppm).

10 Min.

Erwartete Ergebnisse

The calibration curve should be linear from 0 to 10 ppm. The deep red color of [Fe(SCN)]²⁺ intensifies with increasing Fe³⁺ concentration. The water sample's iron content is determined from the calibration curve.

Aufräumen

Collect all thiocyanate-containing solutions in labeled waste. Rinse all glassware thoroughly. Wipe down the colorimeter.

Details

Kategorie
Colorimetry
Schwierigkeit
Intermediate (High School)
Dauer
75 Min.
Geschätzte Kosten
$10,00
Schritte
7
Materialien
5

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Frequently Asked Questions

What is the objective of Eisenbestimmung in Wasser?
Die Konzentration von Eisen(III) in einer Wasserprobe mithilfe der kolorimetrischen Thiocyanatmethode bestimmen.
How difficult is Eisenbestimmung in Wasser?
This experiment is rated as Intermediate (High School). It takes approximately 75 minutes to complete.
What safety precautions are needed for Eisenbestimmung in Wasser?
Key safety precautions include: FeCl₃ solution stains skin and clothing; KSCN is harmful if swallowed; HNO₃ is corrosive — handle with care.
What materials are needed for Eisenbestimmung in Wasser?
The main materials required are: Iron(III) chloride (FeCl₃) standard, Potassium thiocyanate (KSCN), Dilute HNO₃ (0.1 M), Water sample, Distilled water.
What results should I expect from Eisenbestimmung in Wasser?
The calibration curve should be linear from 0 to 10 ppm. The deep red color of [Fe(SCN)]²⁺ intensifies with increasing Fe³⁺ concentration. The water sample's iron content is determined from the calibration curve.