Precipitation Titration: Principal, Ideal Properties and Precaution; MCQ with Answers

1. Precipitation Titration :-

It is also known as Argintometric Titration.

It is type of titremetric procedure involves the formation of precipitate during the course of Titration.

Ideal properties for precipitation Titration :-

• It must be rapid and quantitative.
• It must give insoluble precipitates at end point.
• It must not affecting by co-precipitation or post precipitation.
• Indicator must provide clean and miscible end point.

Principal of precipitation Titration :-

The main principal of the precipitation titration is that the quantity of the added precipitating reagent or precipitant is equivalent to the substance being precipitated.

According to end point detection precipitation Titration method are divided into three types 

1. Mohr method
2. Volhard method
3. Fajan’s method

1. Mohr method :-

This method utilizes chromate as an indicator chromates form a precipitation with Ag but this precipitation has a greater solubility than that of AgCl.

Ex. AgCl is formed first and after all cl is consuming than AgNO3 ppt formation are starting.

Precaution during Mohr method :-

1.  Reaction always carried at 6.5- 9 pH.
2. If the solution is acidic chromates ion decrease.
3. If the solution is Basic silver hydroxide ppt formation.

Estimation of chloride by mohr method :-

In this method cl ion solution is directly titrated against AgNO3 using potassium chromate.

AgNO3 + cl → AgCl + NO3

At the end point, when all the chloride ion are consumed. The yellow colour of chromate change into reddish brown due to following reaction

AgNO3 + K2Cro4 → Ag2cro4 + KNO3

procedure :-

20 ml of the given water sample is pipette out into a clean conical flask.

1 ml of freshly prepared potassium chromates solution is added as an indicator and titrated against standard AgNO3 solution taken in the burette.

The end point is the change of colour from yellow to reddish brown colour.

Calculation :-

Volume of AgNO3 used V1 =

Normality of AgNO3 N1 =

Volume of sample V2 =

Normality of sample N2=

N2 = V1×N1/V2

Normality of water sample N2 =

MCQ

1. Which Titration is known as the Argintometric titration?

A. Acid base Titration

B. Diazotization Titration

C. Gravimetry

D. PRECIPITATION TITRATION

2. Which sentence is false about preparation Titration ?

A.It must be rapid and quantitative.

B.It must give insoluble precipitates at end point.

C. It must not affecting by co-precipitation or post precipitation.

D. It must be slow and quantitative.

3. Which type of solution is used in Mohr method ?

A. Strong acid

B. Strong base

C. Neutral

D. A and B

4. If acidic solution are used in Mohr method

A. Chromates ion are decreased

B. Chromates ion are increased

C. A and B

D. None of the above

5. If the solution is Basic in nature in Mohr method what Happened ?

A. Silver hydroxide ppt formation is Decreased

B. Silver hydroxide ppt formation is increased

C. A and B

D. None of the above

6. End point colour in Mohr method is

A. Red colour

B. Blue colour

C. Yellow colour

D. Black colour

7. PRECIPITATION TITRATION are classified by which mechanism ?

A. Adsorption

B. Colour at end point

C. Ion exchange

D. All of the above

Answer key

1. D

2. D

3. C

4. A

5. B

6. A

7. B

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