Testes de Identificação de Ânions

Detecção de ânions comuns por reações químicas seletivas

Qualitative Analysis Intermediate (High School) 60 min ~$10,00

Objetivo

Identificar ânions desconhecidos usando testes específicos de precipitação, decomposição ácida e redox.

Contexto

Anion analysis complements cation identification in classical qualitative analysis. Unlike cations, anions do not follow a single systematic separation scheme. Instead, they are identified through a series of specific tests: chloride with silver nitrate, sulfate with barium chloride, carbonate with acid, and so on. Understanding these tests reinforces knowledge of solubility rules and reaction types.

Avisos de segurança

  • AgNO₃ stains skin and clothing permanently
  • Use dilute acids only — concentrated acids can produce toxic gases
  • BaCl₂ is toxic if ingested
  • Dispose of silver waste in designated containers

EPI necessário

goggles gloves lab_coat

Materiais

  • Unknown anion solution (10 mL)
    Prepared by instructor
  • Silver nitrate (0.1M AgNO₃) (10 mL)
    For halide tests
  • Barium chloride (0.1M BaCl₂) (5 mL)
    For sulfate test
  • Dilute HNO₃ (2M) (10 mL)
    Acidification
  • Dilute H₂SO₄ (1M) (5 mL)
    For carbonate test
  • Limewater (Ca(OH)₂ solution) (10 mL)
    CO₂ detection
  • Brown ring test reagent (FeSO₄) (5 mL)
    For nitrate test

Equipamentos

Test tubes (8) Dropper pipettes Bunsen burner Delivery tube Test tube rack

Procedimento

1

Carbonate test: Add dilute H₂SO₄ to 2 mL of unknown solution and pass any gas through limewater. A milky appearance confirms CO₃²⁻.

8 min
2

Sulfate test: Add BaCl₂ solution to 2 mL of unknown acidified with HNO₃. A white precipitate insoluble in acid confirms SO₄²⁻.

8 min
3

Chloride test: Add AgNO₃ to 2 mL of unknown acidified with HNO₃. A white curdy precipitate soluble in NH₄OH confirms Cl⁻.

8 min AgNO₃ stains skin
4

Bromide test: Add AgNO₃ as above. A pale yellow precipitate slightly soluble in NH₄OH confirms Br⁻.

8 min
5

Iodide test: Add AgNO₃ as above. A yellow precipitate insoluble in NH₄OH confirms I⁻.

8 min
6

Nitrate test (brown ring): Layer concentrated H₂SO₄ under a mixture of unknown solution and FeSO₄. A brown ring at the junction confirms NO₃⁻.

10 min Handle concentrated H₂SO₄ with extreme care
7

Record all observations, precipitate colors, and solubility behavior. Cross-reference results to identify the anion(s) present.

10 min

Resultados esperados

Each anion produces a characteristic response: carbonates effervesce with acid, sulfates give a white BaSO₄ precipitate, halides give colored AgX precipitates, and nitrates produce a brown ring.

Limpeza

Collect silver-containing waste separately. Neutralize acid waste before disposal. Rinse all glassware thoroughly.

Detalhes

Categoria
Qualitative Analysis
Dificuldade
Intermediate (High School)
Duração
60 min
Custo estimado
$10,00
Passos
7
Materiais
7

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Frequently Asked Questions

What is the objective of Testes de Identificação de Ânions?
Identificar ânions desconhecidos usando testes específicos de precipitação, decomposição ácida e redox.
How difficult is Testes de Identificação de Ânions?
This experiment is rated as Intermediate (High School). It takes approximately 60 minutes to complete.
What safety precautions are needed for Testes de Identificação de Ânions?
Key safety precautions include: AgNO₃ stains skin and clothing permanently; Use dilute acids only — concentrated acids can produce toxic gases; BaCl₂ is toxic if ingested.
What materials are needed for Testes de Identificação de Ânions?
The main materials required are: Unknown anion solution, Silver nitrate (0.1M AgNO₃), Barium chloride (0.1M BaCl₂), Dilute HNO₃ (2M), Dilute H₂SO₄ (1M).
What results should I expect from Testes de Identificação de Ânions?
Each anion produces a characteristic response: carbonates effervesce with acid, sulfates give a white BaSO₄ precipitate, halides give colored AgX precipitates, and nitrates produce a brown ring.