Mohr Titration Method

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Questions and Answers

What is crucial for obtaining accurate results when using silver nitrate titration?

  • Proper standardization of the silver nitrate titrant (correct)
  • Carrying out the titration in a dark environment
  • Avoiding the use of gloves
  • Using colored glassware

Which factor can interfere with the determination of the endpoint in a titration?

  • Use of appropriate glassware
  • Conducting the titration in adequate lighting
  • Presence of reducing agents in the solution (correct)
  • Minimizing the number of trials conducted

Why is it problematic to determine bromide or iodide ions in certain conditions?

  • They are always present in low concentrations
  • They do not react with silver nitrate
  • Chloride ions can significantly interfere with the results (correct)
  • They require a higher pH for accurate measurement

What is an essential safety precaution when handling chemicals during titration?

<p>Using appropriate safety equipment like gloves and eye protection (C)</p> Signup and view all the answers

What type of ions can affect the accuracy of the titration results?

<p>Any interfering metal ions (B)</p> Signup and view all the answers

What is the primary role of the silver nitrate solution in Mohr titration?

<p>To act as a titrant that reacts with halide ions (D)</p> Signup and view all the answers

Which color change indicates the endpoint of a Mohr titration?

<p>From yellow to reddish-brown (C)</p> Signup and view all the answers

What is formed when excess silver ions react with chromate ions at the endpoint?

<p>Silver chromate (B)</p> Signup and view all the answers

Which of the following halide ions can be determined using Mohr titration?

<p>Chloride ions (D)</p> Signup and view all the answers

Which factor does NOT affect the accuracy of Mohr titration?

<p>Volume of analyte solution (D)</p> Signup and view all the answers

What type of solution is prepared to start a Mohr titration?

<p>An unknown analyte solution containing a halide ion (A)</p> Signup and view all the answers

What is the function of potassium chromate in Mohr titration?

<p>To serve as a visual indicator by changing color (B)</p> Signup and view all the answers

During the titration process, what must be done continuously for accurate results?

<p>Use a constant stirring motion (B)</p> Signup and view all the answers

Flashcards

Effect of oxidizing/reducing agents

The presence of substances like oxidizing or reducing agents in the solution can influence the reaction's outcome.

Interference of other ions

The presence of other ions in the solution can interfere with the reaction, leading to inaccurate results.

Limitation of the method

The method is not suitable for determining bromide or iodide ions when chloride ions are present in large amounts.

Effect of colored ions

The presence of coloured ions can make it difficult to determine the endpoint of the titration.

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pH sensitivity

The reaction is sensitive to changes in pH, which can significantly affect the outcome.

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Mohr Titration

A technique using a solution of known concentration (titrant) to determine the concentration of an unknown substance (analyte). The endpoint is marked by a visible color change, often a precipitate.

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Titrant

The solution with a known concentration used to react with the analyte in a titration.

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Analyte

The substance whose concentration you want to determine.

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Precipitation Reaction

A chemical reaction that forms a solid that doesn't dissolve in the solution (precipitate).

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Indicator

A substance that changes color to indicate the endpoint of a titration.

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Endpoint

The point in a titration where the reaction is complete.

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Potassium Chromate

The substance that is added to the solution to indicate the endpoint of the titration by forming a precipitate.

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Interfering Ions

The presence of other substances that interfere with the reaction, affecting the accuracy.

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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.

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