Identification des Cations par Précipitation

Séparation systématique des cations des groupes I-V avec des réactifs sélectifs

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

Objectif

Identifier les cations inconnus dans une solution à l'aide du schéma classique d'analyse qualitative avec des réactifs de groupe.

Contexte

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.

Avertissements de sécurité

  • 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

EPI requis

goggles gloves lab_coat

Matériaux

  • 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

Équipement

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

Procédure

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

Résultats attendus

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.

Nettoyage

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

Détails

Catégorie
Qualitative Analysis
Difficulté
Intermediate (High School)
Durée
90 min
Coût estimé
$12,00
Étapes
7
Matériaux
7

Plus d'expériences

Arc-en-ciel d'Indicateurs de pH 45 min Chromatographie des Pigments Végétaux 60 min Défi d'Identification de Substances Inconnues 75 min Spectroscopie d'Émission de Flamme 60 min Test Amidon-Iode pour les Glucides 30 min Test de Beilstein pour les Halogènes 25 min Test de Dureté de l'Eau avec une Solution Savonneuse 40 min Test de Perle de Borax pour les Ions Métalliques 45 min Tests d'Identification des Anions 60 min

Frequently Asked Questions

What is the objective of Identification des Cations par Précipitation?
Identifier les cations inconnus dans une solution à l'aide du schéma classique d'analyse qualitative avec des réactifs de groupe.
How difficult is Identification des Cations par Précipitation?
This experiment is rated as Intermediate (High School). It takes approximately 90 minutes to complete.
What safety precautions are needed for Identification des Cations par Précipitation?
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 Identification des Cations par Précipitation?
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 Identification des Cations par Précipitation?
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.