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

-

           ✯Titration✯ 

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

★ A solution of known concentration is known as a titrant.
★ A solution of unknown concentration is known as an analyte or titrand.

Precipitation titration—

• PPT titration is a type of titration that involves the formation of precipitate during the titration techniques.

• In ppt titration, the titrant react with analyte and forms an insoluble substance called precipitate It continuously fills until 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 first given by German chemist Jawb Volhard in 1874.

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

• In this method the 1st analyte (Cl) is titrated with excess AgNO₃. .

• It is a type of back titration, so two types of titrant are used.
Type 1-standardized AgNO₃
Type 2—KSCN—potassium thiocyanate 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 a 10 ml sample of NaCl & a few drops of indicators in a conical flask.
★ Titrate the solution with 0.1 AgNO₃; at the end point, a pink color is produced on the surface of the AgCl precipitation.
★ At the end point, a reading is taken from the burette, and the concentration of the sample is calculated.

Step 2 

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

Modified Volhard's method—

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

Fajan's method—

★ This method was given by American chemist Kazimierz Fajans.
★ This method is known as the indicator adsorption method because in this method chloride ions present in excess are adsorbed on the silver chloride surface.
★ In this method dichlorofluoroscein is used as an indicator.
★ It is a direct titration method.
★ It is used to determine chloride, bromide, and iodide.

Principle:


NaCl     +      AgNOჳ    →   AgCl       + NaNOჳ
(Excess)
AgCl    +   AgNOჳ     +   Indicator
                       ⇅                     ⇅
AgCl     +   Ag ๋    + NOჳ¯  Fluorescein
                    ⇅
           AgCl   +  Fluorescein 
 (This complex gives pink color.)

Methodology: 

★ Take a 10 ml sample of NaCl & a few drops of indicators in a conical flask.
★ Titrate the solution with 0.1N AgNO₃ at the end point; a pink color is produced on the surface of AgCl precipitation.
★ At the end point, a reading is taken from the burette, and the concentration of the sample is calculated.
   

Mohr's method—

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

Principle:

NaCl  +    AgNOჳ       →       AgCl     +  NaNOჳ
K₂CrO₄ + 2AgNO₃ → Ag₂CrO₄ + 2KNO₃
(reddish-brown ppt)


Methodology—

★ Titration of 0.1N NaCl by using 0.1N AgNO₃ in the presence of an indicator (5% solution) in a conical flask.
★ At the end point reddish-brown precipitation was obtained.
★ Reading is taken from the burette & the concentration of the unknown sample is calculated.

Application of precipitation titration—

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



Comments

Post a Comment

Popular posts from this blog

B.pharma 1st semester Notes pharmaceutical analysis unit - 4th- Redox Titrations

-
Image
          //  Redox Titrations \\ • A Redox titration is a type of titration in which titrant and titrand react through and oxidation reduction reaction. • The end point of a Redox titration is detected by using indicators. Principles of Redox titration; Reduction—  • The subtances  can undergo reduction by followin. • The addition of hydrogen. •The removal of oxygen. • The acceptance of electrons. Example- fe³+→fe ²+  Oxidation— • Addition of oxygen. • Removal of hydrogen. • Loss/ donation of electrons. Example- fe²+ → fe³+ Oxidising agents;  •An oxidising agent is a chemical species that causes that other reactant in a redox reaction to be oxidized, and it is always reduced in the process. Example- Ag + , O², O³
Read more

B.pharm 2nd semester topic- Nucleic acid

-
                - Nucleic acid • Nucleic acid is an important class of macromolecules found in all cells and viruses.  The function of Nucleic acid -"the storage and expression of genetic information". Nucleic acid is information carrying- molecules of the cell, Nucleic acid, naturally Occurring- chemical compound. • that is capable of being broken down to yield  phosphoric acid sugar and a mixture of organic bases (purine and pyrimidine). The two main classes of nucleic acid; 1. DNA( Deoxyribonucleic acid) 2. RNA( Ribonucleic acid    Basic structure; • Nucleic acid a polynucleotide that is long chain like molecule composed of a series of nearly identical building blocks called nucleotide. • nucleotide consists of pentose (5 carbon) sugar phosphate group possible nitrogen containing bases adenine, guanine ,cytosine,  thymine and Uracil. •Adenine and guanine are categorised are purines •Cytosine thymine and uracil are colle...
Read more