Mohr Titration Method

Study Notes

Introduction

Mohr titration is a volumetric method for determining the concentration of a substance (analyte) using a solution of known concentration (titrant).
Silver nitrate (AgNO₃) is the common titrant.
The endpoint is visually observed by the formation of a precipitate (light-colored against a darker background).

Principle

The titration relies on a precipitation reaction between the analyte and the silver nitrate titrant.
Frequently, the analyte is a halide ion (Cl⁻, Br⁻, I⁻).
The result is a slightly soluble silver salt (AgCl, AgBr, or AgI).
The endpoint is marked by a color change (appearance or disappearance).
Silver ions (Ag⁺) react with halide ions (X⁻) to form a silver halide precipitate (AgX).
A chromate indicator (CrO₄²⁻) is essential.

Indicator

Potassium chromate (K₂CrO₄) is the indicator for Mohr titration.
Potassium chromate gives the solution a yellow color.
When all halide ions are reacted, extra silver ions react with chromate ions, forming a reddish-brown precipitate of silver chromate (Ag₂CrO₄).
This color change (yellow to reddish-brown) signifies the endpoint.

Procedure

Prepare a standard silver nitrate (AgNO₃) solution with a known concentration.
Prepare a solution of the unknown analyte (halide ion).
Add a few drops of potassium chromate indicator to the analyte solution.
Gradually add the standard silver nitrate solution to the analyte solution, while stirring continuously.
Observe the color change.
The endpoint is marked by the first permanent reddish-brown color.
Note the volume of silver nitrate solution used to reach the endpoint.

Applications

Used to determine halide ion concentrations (chloride, bromide, iodide) in various samples.
Implemented in industrial settings and chemistry labs for quality control.
Useful for analysis of chlorine and chloride in water samples.
Used to measure chloride content in different materials and substances.

Factors Affecting Accuracy

Interfering ions can influence the results.
Solution pH can affect the reaction.
Temperature changes impact the reaction.
Proper stirring ensures uniform reactant mixing.
Indicator concentration plays a role in accuracy.
The quality of the standard silver nitrate solution is vital.
Oxidizing or reducing agents present can affect the results.
Presence of other ions can interfere with the reaction.

Precautions

Prevent chemical spills.
Use appropriate personal protective equipment (PPE).
Manage chemical waste properly.
Handle glassware appropriately.
Accurate standardization of the silver nitrate titrant is crucial for reliable results.
Conduct titrations in a well-lit space.

Limitations

Mohr titration isn't suitable for determining bromide or iodide in the presence of substantial amounts of chloride.
It can't reliably analyze mixtures of different halide ions.
Colored ions can interfere with endpoint detection.
The reaction is sensitive to pH fluctuations.
The presence of other metal ions can influence the findings and lead to inaccurate data.

Description

Test your understanding of the Mohr titration method, a volumetric technique that utilizes silver nitrate to determine halide ion concentrations. This quiz covers the principles, reaction processes, and indicators involved in the titration. Enhance your knowledge about precipitation reactions and endpoint determination in titrations.