Titration of Chlorides

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Questions and Answers

What type of adsorption indicator is used when the titrant is Ag+?

Cationic dye

Zwitterionic dye

Anionic dye (correct)

Neutral dye

What is the primary requirement for the precipitate in Fajan's method?

It should be in the crystalline state

It should be in the dissolved state

It should be in the colloidal state (correct)

It should be in the gas state

Why should the sample solution not be too dilute in Fajan's method?

Because the amount of precipitate formed will be small (correct)

To increase the rate of titration

To avoid precipitation of unwanted compounds

To obtain a sharp end point

What is the purpose of using anionic adsorption indicators in Silver Nitrate titrations?

To detect the end point of the titration Signup and view all the answers

What is the characteristic of weak acid adsorption indicators like Eosin and Fluorescein?

They can donate a proton (H+) Signup and view all the answers

Why can't eosin (tetrabromo fluorescein) be used in the titration of Cl- with Ag+?

It is strongly adsorbed by the precipitate before the equivalence point Signup and view all the answers

What is the main advantage of using adsorption indicators in Fajan's method?

They provide a sharp end point Signup and view all the answers

What is the purpose of using Rhodamine-6-G as an adsorption indicator?

To detect the end point of the titration when the titrant is Cl- Signup and view all the answers

Why is fluorescein not suitable for titration in slightly acid solutions?

It is a very weak acid Signup and view all the answers

What is the minimum pH range for using dichlorofluorescein as an indicator?

pH 4.4 Signup and view all the answers

What is the advantage of using eosin as an indicator?

It can be used in highly acidic solutions Signup and view all the answers

What is the purpose of adjusting the pH of the solution during a titration?

To ensure the indicator remains in its ionic form Signup and view all the answers

Why should titrations with adsorption indicators be carried out with a minimum exposure to sunlight?

To ensure silver halides are not sensitized to the action of light Signup and view all the answers

What type of complex is formed during the titration of silver in the presence of free nitric acid with standard potassium thiocyanate or ammonium thiocyanate solution?

Soluble colored complex Signup and view all the answers

Which of the following indicators is suitable for the titration of iodides?

Rose Bengal Signup and view all the answers

What is the color of the precipitate at the end point during the titration of cyanide ion with standard silver diphenylcarbazide nitrate solution?

Pale violet Signup and view all the answers

Study Notes

Principle of Adsorption Indicators

Used to determine chloride, bromide, iodide, thiocyanate, etc.
Method employs adsorption indicators to detect endpoint
Adsorption indicators are organic acidic or basic dyes with 2 different colors:
- One color when not adsorbed (in solution)
- Different color when adsorbed on the ppt at the endpoint

Conditions for Choosing a Suitable Adsorption Indicator

Precipitate should be in the colloidal state to maximize indicator adsorption
Precipitate must strongly adsorb its own ions
Sample solution should not be too dilute to ensure a sharp endpoint
Indicator ion must be of opposite charge to the ion of the precipitating agent
Indicator ion should not be adsorbed before the particular compound is completely precipitated
Concentration of indicator must not precipitate during titration or after the endpoint
pH of the solution must be adjusted such that the ionic form of the indicator predominates

Examples of Adsorption Indicators

Eosin (tetrabromo fluorescein): can be used for I-, Br-, or SCN- but not Cl- due to strong adsorption before the equivalence point
Fluorescein: can be used for Cl- and has an optimum pH range of 7-10
Dichlorofluorescein: stronger acid than fluorescein, applicable in slightly acid solutions of pH > 4.4, and can be used in more dilute solutions
Eosin (tetrabromofluorescein): stronger acid, can be used down to pH 1-2, and has a sharpest color change in an acetic acid solution (pH < 3)
Rose Bengal (dichloro tetraiodo fluorescein) and dimethyl diiodo-fluorescein: recommended for the titration of iodides
Other dye-stuffs have been recommended as adsorption indicators for the titration of halides and other ions

Disadvantage of Adsorption Indicators

Silver halides are sensitized to the action of light by the layer of adsorbed indicator, so titrations should be carried out with a minimum exposure to sunlight

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Description

This quiz covers the principles and conditions of titration of chlorides, including the use of indicators and the adjustment of pH. It also discusses the importance of concentration and ionic form of the indicator.