Titulação por Precipitação (Método de Mohr)

Determinação da concentração de cloreto usando nitrato de prata

Titrations Advanced (University) 45 min ~$20,00

Objetivo

Determinar a concentração de íons cloreto em uma solução usando o método de Mohr, onde o nitrato de prata é o titulante e o cromato de potássio é o indicador.

Contexto

In the Mohr method, silver nitrate reacts with chloride ions to form white silver chloride precipitate. When all chloride is consumed, the first excess silver reacts with the chromate indicator to form brick-red silver chromate, signaling the endpoint. This method works at near-neutral pH.

Avisos de segurança

  • Silver nitrate stains skin and clothing permanently
  • Potassium chromate is toxic and a suspected carcinogen — handle with extreme care
  • Wear nitrile gloves and safety goggles
  • Dispose of silver and chromate waste in designated containers

EPI necessário

goggles gloves lab_coat

Materiais

  • Sodium chloride solution (100 mL)
    Unknown concentration
  • Silver nitrate (AgNO₃) (100 mL)
    0.1M standardized
  • Potassium chromate (K₂CrO₄) (10 mL)
    5% indicator solution
  • Distilled water (200 mL)

Equipamentos

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

Procedimento

1

Pipette 25.0 mL of the chloride solution into the Erlenmeyer flask.

2 min
2

Add 1 mL of 5% potassium chromate indicator. The solution turns pale yellow.

1 min Chromate is toxic — use minimal amount
3

Fill the burette with 0.1M AgNO₃. Record the initial volume.

3 min AgNO₃ stains permanently
4

Titrate while swirling vigorously. A white precipitate of AgCl forms.

10 min
5

Near the endpoint, the precipitate becomes more curd-like. Add AgNO₃ drop by drop until a permanent brick-red color of Ag₂CrO₄ appears.

5 min
6

Record the volume. Repeat for concordant results.

15 min
7

Calculate chloride concentration: C(Cl⁻) = C(Ag+) x V(AgNO₃) / V(sample).

5 min

Resultados esperados

The endpoint is marked by the first permanent appearance of a brick-red color due to Ag₂CrO₄ formation. This color should persist for at least 30 seconds after swirling.

Limpeza

Collect all silver-containing waste in the designated heavy metal waste container. Collect chromate waste separately. Never dispose down the drain. Wash hands thoroughly.

Detalhes

Categoria
Titrations
Dificuldade
Advanced (University)
Duração
45 min
Custo estimado
$20,00
Passos
7
Materiais
4

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Frequently Asked Questions

What is the objective of Titulação por Precipitação (Método de Mohr)?
Determinar a concentração de íons cloreto em uma solução usando o método de Mohr, onde o nitrato de prata é o titulante e o cromato de potássio é o indicador.
How difficult is Titulação por Precipitação (Método de Mohr)?
This experiment is rated as Advanced (University). It takes approximately 45 minutes to complete.
What safety precautions are needed for Titulação por Precipitação (Método de Mohr)?
Key safety precautions include: Silver nitrate stains skin and clothing permanently; Potassium chromate is toxic and a suspected carcinogen — handle with extreme care; Wear nitrile gloves and safety goggles.
What materials are needed for Titulação por Precipitação (Método de Mohr)?
The main materials required are: Sodium chloride solution, Silver nitrate (AgNO₃), Potassium chromate (K₂CrO₄), Distilled water.
What results should I expect from Titulação por Precipitação (Método de Mohr)?
The endpoint is marked by the first permanent appearance of a brick-red color due to Ag₂CrO₄ formation. This color should persist for at least 30 seconds after swirling.