Complexometric Titrations Flashcards

Flashcards generated from lecture notes on Complexometric Titrations focusing on definitions, requirements, titration types, and masking/demasking techniques.

What is a metallochromic indicator?

A compound whose color changes when it binds to a metal ion.

What is a key requirement for a metallochromic indicator to be useful in EDTA titrations?

It must bind to the metal less strongly than EDTA does.

Why are most metallochromic indicators used in specific pH ranges?

Most of these indicators are acid-base indicators, and their color is pH-dependent.

What are the requirements of a suitable metallochromic indicator?

Stability of (M—In) complex must be less than the stability of (M — EDTA) complex. The metal-indicator complex must possess sufficient stability. The change in equilibrium from (M—In) to (M—EDTA) should be sharp & rapid. The indicator must be very sensitive to metal ions so that the color change occurs as near to the equivalence point as possible. These requirements must be fulfilled within the pH of the titration.

What is indicator blocking?

When indicator forms a complex with a metal whose stability constant is greater than that of the metal- EDTA complex

Name the types of EDTA titrations.

Direct titration, Back titration, Displacement titration, Alkalimetric titration, and Indirect titration.

Give an example when auxiliary complexing agent is used.

In direct titration of Pb 2+ is carried out in ammonia buffer pH 10 in presence of tartarate which complexes the metal to prevent formation of Pb(OH)2 to precipitate.

What are the conditions when back titrations are used?

The analyte precipitates in the absence of EDTA, the analyte reacts too slowly with EDTA, or the analyte (metal) blocks the indicator.

What is displacement titration?

A titration where the analyte is treated with excess Mg(EDTA)2- chelate to displace Mg 2+ which is then titrated with standard EDTA.

What is alkalimetric titration?

When a solution of Na 2 EDTA is added to metallic ions, complexes are formed with liberation of two equivalent hydrogen ions, where the hydrogen ion liberated is titrated with a standard of sodium hydroxide.

What is indirect titration?

Anions that form a precipitate with certain metal ions may be analyzed with EDTA by indirect titration after precipitating and dissolving the precipitate.

What is a masking agent?

A reagent that protects some component of the analyte from reaction with EDTA without physical separation.

How does masking affect the selectivity of EDTA?

Masking increases the selectivity of EDTA by preventing certain metal ions from reacting with EDTA, allowing for the titration of other ions in the mixture.

What is Demasking?

It is the release of a metal ion from a masking agent.

How do you increase EDTA selectivity?

Masking and demasking, Suitable control of the pH of the solution, Classical separation and Solvent extraction.

What is the role of pH in EDTA titrations?

The pH affects the stability of metal-EDTA complexes and can influence the color change of metallochromic indicators.

What are some common applications of EDTA titrations?

EDTA titrations are commonly used in water quality testing, metal ion analysis, and determining hardness in water.

What is the significance of the equivalence point in EDTA titrations?

The equivalence point indicates the completion of the reaction between the metal ion and EDTA, signifying that all available metal ions have reacted.

How can the results of EDTA titrations be expressed?

Results can be expressed in terms of concentration of metal ions,

What is the purpose of using EDTA in titrations?

EDTA is a chelating agent that forms stable complexes with metal ions, allowing for accurate quantification of these ions in solution.

What happens at the endpoint of an EDTA titration?

At the endpoint, a color change occurs due to the addition of a metallochromic indicator, indicating that all the metal ions have reacted with EDTA.

What factors can affect the accuracy of EDTA titrations?

Factors include the pH of the solution, the type of indicator used, the presence of interfering ions, and the concentration of the metal ions.

Why is pH control important during EDTA titrations?

Control of pH is essential as it influences both the stability of metal-EDTA complexes and the behavior of the metallochromic indicators.

What are auxiliary complexing agents, and why are they used?

Auxiliary complexing agents are substances added to stabilize metal ions and prevent the formation of insoluble precipitates during titrations.