Kationenidentifikation durch Fällung

Systematische Trennung der Kationen der Gruppen I–V mit selektiven Reagenzien

Qualitative Analysis Intermediate (High School) 90 Min. ~$12,00

Ziel

Unbekannte Kationen in einer Lösung mithilfe des klassischen qualitativen Analyseschemas mit Gruppenreagenzien identifizieren.

Hintergrund

Classical qualitative analysis divides cations into five analytical groups based on their solubility with specific reagents. Group I cations (Ag⁺, Pb²⁺, Hg₂²⁺) precipitate with dilute HCl. Group II (Cu²⁺, Bi³⁺, Cd²⁺) precipitate with H₂S in acidic solution. This systematic approach was developed in the 19th century and remains a cornerstone of analytical chemistry education.

Sicherheitswarnungen

  • H₂S is toxic — work in fume hood at all times
  • Wear gloves when handling concentrated reagents
  • Never mix reagents without understanding the expected reaction
  • Dispose of heavy metal solutions in designated waste containers

Erforderliche PSA

goggles gloves lab_coat

Materialien

  • Unknown cation solution (10 mL)
    Prepared by instructor
  • Dilute HCl (2M) (20 mL)
    Group I reagent
  • H₂S solution or thioacetamide (10 mL)
    Group II reagent
  • NH₄OH (6M) (10 mL)
    Group III reagent
  • (NH₄)₂CO₃ solution (10 mL)
    Group IV reagent
  • NaOH (6M) (10 mL)
    Confirmation tests
  • Distilled water (100 mL)
    For washing precipitates

Ausrüstung

Test tubes (10) Centrifuge Hot water bath Dropper pipettes Test tube rack Wash bottle

Durchführung

1

Add 1 mL of 2M HCl to 5 mL of unknown solution. If a precipitate forms, centrifuge and separate the supernatant from the Group I precipitate.

10 Min.
2

Test the Group I precipitate: wash with hot water (PbCl₂ dissolves), then add NH₄OH (AgCl dissolves forming [Ag(NH₃)₂]⁺).

10 Min.
3

To the supernatant from Step 1, add thioacetamide or H₂S in acidic conditions. Centrifuge any Group II precipitate.

15 Min. Use fume hood for H₂S
4

Make the supernatant basic with NH₄OH and add (NH₄)₂S. Centrifuge any Group III precipitate (Fe, Al, Cr hydroxides).

15 Min.
5

To the remaining solution, add (NH₄)₂CO₃. Group IV cations (Ca²⁺, Ba²⁺, Sr²⁺) precipitate as carbonates.

10 Min.
6

The remaining solution contains Group V cations (Na⁺, K⁺, NH₄⁺). Confirm with flame tests or specific reagent tests.

15 Min.
7

Perform confirmation tests on each group precipitate and record your findings.

15 Min.

Erwartete Ergebnisse

Each analytical group should produce characteristic precipitates with specific colors. Confirmation tests (flame tests, specific reagents) identify the individual cations present in the unknown solution.

Aufräumen

Collect all heavy metal waste in labeled containers. Rinse test tubes three times with distilled water. Clean centrifuge tubes thoroughly.

Details

Kategorie
Qualitative Analysis
Schwierigkeit
Intermediate (High School)
Dauer
90 Min.
Geschätzte Kosten
$12,00
Schritte
7
Materialien
7

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Frequently Asked Questions

What is the objective of Kationenidentifikation durch Fällung?
Unbekannte Kationen in einer Lösung mithilfe des klassischen qualitativen Analyseschemas mit Gruppenreagenzien identifizieren.
How difficult is Kationenidentifikation durch Fällung?
This experiment is rated as Intermediate (High School). It takes approximately 90 minutes to complete.
What safety precautions are needed for Kationenidentifikation durch Fällung?
Key safety precautions include: H₂S is toxic — work in fume hood at all times; Wear gloves when handling concentrated reagents; Never mix reagents without understanding the expected reaction.
What materials are needed for Kationenidentifikation durch Fällung?
The main materials required are: Unknown cation solution, Dilute HCl (2M), H₂S solution or thioacetamide, NH₄OH (6M), (NH₄)₂CO₃ solution.
What results should I expect from Kationenidentifikation durch Fällung?
Each analytical group should produce characteristic precipitates with specific colors. Confirmation tests (flame tests, specific reagents) identify the individual cations present in the unknown solution.