Pharmaceutical analysis- Titration and types ( Volhard's , Fajan and mohr's)

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           ✯Titration✯ 

" Titration is a technique used in analytical chemistry to determine concentration of unknown solution by using solution of known concentration."

★ solution of known concentration is known as titrant.
★ Solution of unknown concentration is known as analyte or titrand.

Precipitation titration-;

• ppt titration is a type of titration which involves the formation of pricipital during the titration techniques .

• In ppt titration titrant react with analyte and forms an insoluble substance called precipitate It continuous fill the last amount of analyte is consumed.
It is used to determine chloride by using silver ions. 

 Types / method

1. Volhard's method-;

• This method was 1st given by German chemist" Jawb Volhard's " in 1874.

• This method involves the determination of halides ( F, Cl,Br and I) ions , anions like phosphate chromate in acidic medium by using silver ions.

• In this method 1st analyte ( Cl ) is titrated with excess of AgNOз .

• It is a type of back titration, so two types titrant is used.
 Type 1- standized AgNOз
Type 2- KSCN - potassium thiocynate or NH4CN

Step -1 


Standardisation of AgNOჳ by using 0.1N NaCl 
AgNOჳ +   NaCl   →     AgCl   + NaNOჳ

Step 2nd -; 

Determination of analyte i.e. KCl

KCl     +   AgNOჳ    →      AgCl   +  KNOჳ  + AgNOჳ
(Analyte)  (Excess)        Ppt.

AgNOჳ     +     KSCN       →      AgSCN    + KNOჳ

* Fe๋³   + SCN¯       →   Fe ( SCN ) ๋²
                                       reddish brown ( end point)

Methodology-;

Step-1 

★ Take 10 ml sample of NaCl & few drops of indicators in conical flask.
★ Titrate the solution with 0.1AgNOჳ at the end point pink colour is produced on the surface of AgCl precipitation.
★ At the end point reading is taken from burette & calculate the concentration of sample.

Step-2 

• Take sample solution (i.e 10 ml  KCl ) , add excess of AgNOჳ solution ( 20ml) & add few drops of iron indicator solution.
• Titrate the solution by using standard solution of KSCN or NH4SCN (0.1N) . 
• At the end point radish colour precipitation of Fe (SCN) will occur due to completion of reaction calculate the amount/ concentration of sample ( KCl).

Modified Volhard's method-;

★ Chloroform or nitrogen or other wetting agents are added after addition of AgNOჳ in step 2nd .
★ This modified Volhard's method gives acurate results of titration.
★ These agents form a layer arround the Precipitation of AgCl ↓ & present the solubilization of AgCl.

Fajan's method-;

★ This method was given by American chemist karimierz Fajan.
★ This method is known as indicator adsorption method because in this method chloride ion present in excess are adsorbed on silver chloride surface.
★ In this method dichlorofloroscien is used as an indicator.
★ It is direct titration method.
★ It is used to determine chloride, bromide and iodide.

Principle-;


NaCl     +      AgNOჳ    →   AgCl       + NaNOჳ
                 ( Excess)
AgCl    +   AgNOჳ     +   Indicator
                       ⇅                     ⇅
AgCl     +   Ag ๋    + NOჳ¯  Flouroseien
                    ⇅
           AgCl   +  Flouroseien       
 (This complex gives pink colour)

Methodology-; 

★ Take 10 ml sample of NaCl & few drops of indicators in conical flask.
★ Titrate the solution with 0.1N AgNO ჳ at the end point pink colour is produced on the surface of AgCl precipitation.
★ At the end point reading is taken from burette & calculate the concentration of sample.
   

Mohr's method-;

★ This method was given by Karl Friedrich Mohr.
★ It is direct method of titration silver nitrate is used as titrant and chloride ion solution is titrand.
★ Potassium chromate is used as an indicator.
★ This method is not used for iodide.
★ This method carried out in neutral medium.

Principle-;

NaCl  +    AgNOჳ       →       AgCl     +  NaNOჳ
KշCrO4  +  2AgNOჳ    →   AgշCrO4   + 2KNOჳ
                                             ( redish brown ppt)


Methodology-;

★ Titration of 0.1N NaCl by using 0.1N AgNOჳ in the pressure of indicator ( 5% solution) in conical flask.
★ At the end point reddish brown precipitation obtained.
★ Reading is taken from burette & calculate the concentration of unknown sample.

Application of precipitation titration-;

★ It is used for halide ion solution.
 ★ It is used to measure salt content in food beverage and water.



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