EDTA-Komplexometrie zur Wasserhärtebestimmung

Messung des Calcium- und Magnesiumgehalts in Wasser

Titrations Advanced (University) 45 Min. ~$15,00

Ziel

Die Gesamthärte einer Wasserprobe durch Titration gelöster Ca2+- und Mg2+-Ionen mit EDTA unter Verwendung von Eriochromschwarz T als Indikator bestimmen.

Hintergrund

EDTA (ethylenediaminetetraacetic acid) forms stable 1:1 complexes with metal ions. In the presence of Eriochrome Black T indicator at pH 10, the solution is wine-red when metal ions are present and turns blue when all metal ions are complexed by EDTA, marking the endpoint.

Sicherheitswarnungen

  • Ammonia buffer has a strong odor — use in a ventilated area
  • Wear safety goggles
  • EDTA is generally safe but avoid ingestion

Erforderliche PSA

goggles lab_coat

Materialien

  • Water sample (250 mL)
    Tap water or well water
  • EDTA solution (100 mL)
    0.01M, disodium salt
  • Eriochrome Black T indicator (5 mL)
    Solid or solution
  • Ammonia buffer (pH 10) (20 mL)
    NH₃/NH₄Cl buffer
  • Distilled water (200 mL)

Ausrüstung

50 mL burette Burette stand and clamp 250 mL Erlenmeyer flask 25 mL pipette White tile

Durchführung

1

Pipette exactly 25.0 mL of the water sample into the Erlenmeyer flask.

2 Min.
2

Add 2 mL of ammonia buffer (pH 10) to the flask.

1 Min. Ammonia odor — work in ventilated area
3

Add a small amount of Eriochrome Black T indicator. The solution should turn wine-red.

1 Min.
4

Fill the burette with 0.01M EDTA solution. Record the initial volume.

3 Min.
5

Titrate by adding EDTA slowly while swirling. The wine-red color will gradually shift.

10 Min.
6

Near the endpoint, add EDTA drop by drop until the color changes sharply from wine-red to blue.

5 Min.
7

Record the final volume. Repeat for concordant results.

12 Min.
8

Calculate total hardness in mg/L CaCO₃ equivalent using the formula: Hardness = (V(EDTA) x C(EDTA) x 100.09 x 1000) / V(sample).

5 Min.

Erwartete Ergebnisse

Typical tap water has 100-250 mg/L total hardness (CaCO₃ equivalent). The color change should be a clear transition from wine-red to blue. Soft water requires less EDTA; hard water requires more.

Aufräumen

Dispose of EDTA solutions down the drain (biodegradable at these concentrations). Rinse all glassware.

Details

Kategorie
Titrations
Schwierigkeit
Advanced (University)
Dauer
45 Min.
Geschätzte Kosten
$15,00
Schritte
8
Materialien
5

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Frequently Asked Questions

What is the objective of EDTA-Komplexometrie zur Wasserhärtebestimmung?
Die Gesamthärte einer Wasserprobe durch Titration gelöster Ca2+- und Mg2+-Ionen mit EDTA unter Verwendung von Eriochromschwarz T als Indikator bestimmen.
How difficult is EDTA-Komplexometrie zur Wasserhärtebestimmung?
This experiment is rated as Advanced (University). It takes approximately 45 minutes to complete.
What safety precautions are needed for EDTA-Komplexometrie zur Wasserhärtebestimmung?
Key safety precautions include: Ammonia buffer has a strong odor — use in a ventilated area; Wear safety goggles; EDTA is generally safe but avoid ingestion.
What materials are needed for EDTA-Komplexometrie zur Wasserhärtebestimmung?
The main materials required are: Water sample, EDTA solution, Eriochrome Black T indicator, Ammonia buffer (pH 10), Distilled water.
What results should I expect from EDTA-Komplexometrie zur Wasserhärtebestimmung?
Typical tap water has 100-250 mg/L total hardness (CaCO₃ equivalent). The color change should be a clear transition from wine-red to blue. Soft water requires less EDTA; hard water requires more.