The document provides information about diazotization titrations. It discusses the principle, theory, procedure, end point detection, factors affecting, applications, and advantages/disadvantages of diazotization titrations. The key points are: - Diazotization titrations involve the reaction of a primary aromatic amine with sodium nitrite in acidic medium to form a diazonium salt, which is then titrated. - The end point is detected using an external indicator like starch iodide paper or electrochemically. - Factors like acid concentration, temperature, and reaction time must be controlled. - It can be used to determine drugs and compounds containing

1. R DEEPTHI
Assoc. Professor
Vignan institute of pharmaceutical technology,
Visakhapatnam

2. Diazotization Titrations
INTRODUCTION
• The diazotization titration is nothing but the conversion of the
primary aromatic amine to a diazonium compound.
• This process was first discovered in 1853 and was applied to
the synthetic dye industry.
• The reaction mechanism was first proposed by Peter Griessin.
• In this method, the primary aromatic amine is reacted with the
sodium nitrite in acidic medium to form a diazonium salt.
• This method is first used in the determination of dyes.

3. PRINCIPLE
• The principle involved in this method is that the primary
aromatic amine present in the sample reacts with the sodium
nitrite in the presence of acid such as hydrochloric acid to
obtain a diazonium salt.
R − NH2 + NaNO2 +HCl R − N+ ≡ N − Cl− + NaCl + H2O
• Sodium nitrite is added to the solution of amine in the presence
of acid at 0–5 °C.
• The amine reacts with the nitrous acid to form nitrosamine,
which is followed by the tautomerisation and the water
molecule is lost to form the diazonium ion. This diazonium ion
is stabilized by the displacement of the positive charge at the
ortho and para positions of the ring.
C6H5NH2 + NaNO2 + HCl C6H5N = NCl + NaCl + H2O

4. THEORY
• When sodium nitrite is reacted with the hydrochloric acid
sodium chloride and nitrous acid are formed.
NaNO2 + HCl NaCl + HNO2
• The obtained nitrous acid is reacted with the primary aromatic
amine to form the diazonium salt. The excess of nitrous acid is
removed by the addition of ammonium sulphamate solution.
R − NH2 + HNO2 R − N = NH + H2O
• The end point is detected by the formation of the blue colour
with starch iodide paper. This is prepared by immersing the
filter paper in the starch mucilage and potassium iodide
solution.
KI + HCl KCl + HI
2HI + 2HNO2 I2 + 2NO +2H2O
I2 + starch mucilage blue colour end point

5. PROCEDURE
• The general procedure is followed by weighing the sample(2.5g) and
transferring it into the standard flask (250ml).
• Then add 50mlof concentrated hydrochloric acid and (5g) potassium
bromide are added and the rest of the volume is filled with the
distilled water.
• This resulting solution is known as the standard solution.
• The appropriate volume of the standard solution is pipetted out and
the temperature is maintained at 0-5 °C.
• Then the solution is titrated with the 0.1N sodium nitrite solution
until the starch iodide paper turns into blue colour.
• Another procedure is —After maintaining the conical flask
temperature, the pair of platinum electrodes is immersed. Then the
electrodes are connected to the potentiometer and slowly titrated
with sodium nitrite solution until a permanent deflection is observed
at the end point.

6. END POINT DETECTION
• The end point in diazotization titration is detected by the
following procedures:
• The excess of nitrous acid is determined by the addition of
the starch iodide as an external indicator. After
diazotization, one drop of the resulting solution is placed
on the starch iodide paper which changes into dark colour.
• Another method for the detection of end point is
Electrochemical method: By immersing the platinum
electrodes in the resulting solution and it is also detected
by the dead-stop end point method.
• 0.5g Sample + 10ml HCl + 75ml Water
NaNo2

8. The next method for the detection of the end point in the
diazotization titration is by adding the potassium iodide to the
nitrous acid with excess acid which liberates the iodine.
The liberated iodine is back titrated with the sodium thiosulphate
using starch as the external indicator. The end point is detected by
appearance of blue colour.
KI + HCl HI + KCl
HI + 2HNO2 I2 + 2NO + 2H2O
Preparation and Standardization of the Sodium Nitrite Solution
• Appropriately weighed sodium nitrite is dissolved in the water and
made up to the desired volume.
• Standardization of the sodium nitrite is carried out by titrating the
previously dried sulphanilamide dissolved in the water and
hydrochloric acid solution which is cooled to 15 °C with standard
solution of the sodium nitrite.

9. Preparation and Standardization of 0.1N Sodium Nitrite solution

10. FACTORS AFFECTING THE DIAZOTIZATION
• Acid concentration.
• pH of the NaNO2.
• Temperature of the reaction (should be maintained at 0–5 °C):
the diazonium compounds are decomposed at elevated
temperatures.
• Reaction time (it takes 10–15 min): the compounds react with
nitrous acid at different rates based on the nature of the
compound.
• Slow diazotizable groups: sulpha groups, carboxylic groups
and nitrogen oxide group.
• Fast diazotizing groups: anilide, toluidine and aminophenol.

11. CONDITIONS FOR THE DIAZOTIZATION TITRATION
• The following conditions are required for the diazotization titration of the
amino group containing samples. They are as follows:
• Rate of titration: Addition of sodium nitrite to the sample solution takes
time to react with the amino group present in the sample solution. Different
amino compounds react with the nitrous acid at different rates. Based on
this, the amino compounds are classified into two main groups. They are as
follows:
• Slow diazotizable compounds
Example: Sulphanilic acid and anthranilic acid
• Fast diazotizable compounds
Example: Aniline, aminophenol, and toluidine
• The reaction rate is increased by the addition of the potassium bromide
solution.
• Temperature: Maintenance of the temperature is the main condition for the
diazotization titration. The diazonium salts formed are not stable at elevated
temperatures. They are readily decomposable at elevated temperatures,
therefore, the temperature should be maintained at 0–5 °C.

12. Types of Diazotization Titrations
• There are mainly three types of methods based on the titration
procedure. They are as follows:
Direct method: The main principle involved in this method is to
treat the amino group containing drug with the acid solution.
• The resulting solution is immersed in the cold water bath or
ice water bath by maintaining the temperature at 0–5 °C.
• Then this solution is titrated with the sodium nitrite solution.
The end point is determined by the above-mentioned methods.
Indirect method: The principle involved in this method is that
the excess nitrous acid is added to the titration sample solution
and it is back titrated with the other appropriate titrant. This
method is mainly used for the titration of insoluble diazonium
salts.

13. Other method (Diazo oxide formation method): The main
principle involved in this method is the formation of the diazo
oxide which is more stable than the diazo compounds.
• For example, the aminophenol is readily oxidized by the
nitrous acid and converted to the quinones in the presence of
copper sulphate solution and forms the diazo oxide
compounds.
• This readily undergoes the coupling reaction with the nitrous
acid.

14. ADVANTAGES
• Selective for the all types of sulphonamides.
• Sensitive
• Reproducibility
DISADVANTAGES
• Applicable for a very less variety of samples.
• Relatively slow when compared to other methods.
• Temperature conditions to be properly maintained throughout
the reaction.
• The end point detection is very difficult.
• The colour produced is not stable.
• Lack of specificity.

15. APPLICATIONS
• Used in the determination of the sulphonamides.
Method: An accurately weighed 1 mg sample of sulphonamide is
dissolved in the 4 ml of concentrated HCl and in 10 ml of
distilled water.
Then, this solution is cooled to 15 °C and titrated with the 0.1 M
of sodium nitrite solution.
The end point is determined by streaking one drop of the titration
solution on the starch iodide paper until blue colour is appeared.
The percentage amount of the sulpha drug is determined by the
following equation:
•

16. • where V is the volume of the titrant consumed; M is the
molarity of the titrant; EW is the equivalent weight of the drug;
W is the weight of the sample.
• Used in the determination of the chlorpheneramine.
Method: The accurately weighed sample is added to the 5 ml of
HCl and 50 ml of distilled water. Then the solution is cooled to
15 °C. Then the solution is slowly titrated with the 0.1 N sodium
nitrite solution using starch iodide paper as the indicator.
• Used in the determination of the dopamine, dapsone
• Used in the determination of the procaine, benzocaine
• Used in the determination of the amphetamine.
• Used in the determination of the procaine
• Used in the determination of the ephedrine.
• All sulpha drugs ex: sulphadoxime, sulphacetamide, sodium
amino salicylate

17. • Used in the determination of the P-amino benzoic acid
(vitamin B4).
Method: The accurately weighed sample is added to the 5 ml of
HCl and 50 ml of distilled water. Then the solution is cooled to
15 °C. Then the solution is slowly titrated with the 0.1 N sodium
nitrite solution using starch iodide paper as the indicator.
• 1 ml of 0.1 N sodium nitrite ≡ 0.01371 g of vitamin B4

18. REVIEW QUESTIONS
• What is the principle involved in the diazotization titrimetry?
• What are the conditions required for the diazotization
titrimetry?
• What are the example drugs assayed by the diazotization
titrimetry?
• What are the advantages of diazotization titrimetry?
• What are the factors that affect the diazotization end point?
• What are the different methods used for the end point detection
in the diazotization titrimetry?

19. Conductometry
• INTRODUCTION
• Conductometry is the measurement of the electrical
conductivity of a solution.
• The conductance is defined as the current flow through
the conductor.
• In other words, it is defined as the reciprocal of the
resistance.
• The unit for the conductance is Seimens (S) which is the
reciprocal of Ohm's (Ω−1).
• This method is mainly used for the determination of the
physico-chemical properties of the compounds.

20. • PRINCIPLE
• The main principle involved in this method is that the
movement of the ions creates the electrical conductivity.
The movement of the ions is mainly depended on the
concentration of the ions.
• A+B− + C+D− AD + C+B−
• where A+B− is the solution of strong electrolyte; C+D− is
the solution of the reagent.
• Here the ionic concentration of A+ is determined by
reacting the electrolyte solution with the reagent solution
so that the A+ ions are replaced by the C+ ions. This
replacement of the ions with the other ions shows the
conductance increase or decrease. This is done mainly
by the replacement of the hydrogen ion with other cation.

21. THEORY
The theory is mainly based on Ohm's law which states that the current (I) is directly
proportional to the electromotive force (E) and inversely proportional to the resistance
(R) of the conductor:
I = E/R
The conductance is defined as the reciprocal of the resistance. The resistance is
expressed by the following equation:
R = ρl/a
where ρ is the resistivity; l is the length; a is the cross-sectional area of the
homogenous material.
Therefore,
C = 1/R
= k/la
where K is the conductivity; l is the length; a is the cross-sectional area of the
homogenous material.

22. • Then the molar conductivity is defined as the conductivity due to 1
mole and it is expressed by the following formula:
• Λ = 1,000k/C
• where K is the conductivity; C is the concentration of the solution in
mol/l.
• The sample solution is placed on the cell which is composed of
platinum electrodes. These are calibrated with the help of known
conductivity of the solution, for example, standard potassium
chloride solution.
• Cell constant is defined as the conductivity of the cell:
• R = ρl/a
• where ρ is the resistivity; l is the length; a is the cross-sectional area
of the homogenous material.
• Cell constant = specific conductivity/observed conductivity
• Then the cell constant is determined by the substitution of the value
of the specific conductivity of N/50 KCl solution at 25 °C. The value
is 0.002765 mhos which is given by the Kohlrausch.
• Cell constant = 0.002765/observed conductivity

23. • Methods for the Conductance Measurements
• The conductance of the sample solution is measured by
the resistance measurement by the Wheatstone bridge.
• The following are the different bridges used for the
measurement of the conductance:
• Kohlrausch bridge: It consists of a meter bridge wire AB
with a fixed resistance R on both the ends. To increase
the length of the wire, it is connected to the resistance
box R*, conductance cell C and the head phone D and a
small induction coil I. All these are operated by the
battery.
• Headphone is used for the detection of the conductance
difference.

25. • Conductivity cell: These conductivity cells are made up of
glass. These are commonly employed by dipping in the
analyte solution. It is composed of pair of electrodes
placed at a constant distance. There are mainly three
types of cells used as conductivity cells:
• Type A: This consists of the electrodes placed at a large
distance and is used for the measurement of the high
conductance.
•

26. • Type B: In this type, the cell is dipped in the sample
solution to measure the conductance in the titrations.

27. • Type C: In this type, large electrodes are placed with
small distance. This type cell is mainly used for the
measurement of the low conductance. They are made up
of glass fitted with the platinum electrodes.

28. • APPARATUS
• The conductometric apparatus is composed of the
following. The electrodes are made up of platinum
sheets. These electrodes are fixed in a constant distance
and are sealed in the connected tubes. To avoid the
polarisation effect, these electrodes are coated with the
platinum black. This is done by the 2–3% of the
chloroplatinic acid solution. Then 0.02–0.03 g of lead
acetate solution is taken into the cell. On passing the
current, chloroplatinic acid under goes electrolysis and
the electrodes are blackened. Then these electrodes are
repeatedly washed with the distilled water and finally with
the conductivity water. The conductivity water is the water
obtained by treating the distilled water with small amount
of sodium hydroxide and potassium permanganate. Here
the induction coil is used for inducing current.

29. • METHOD
• The sample solution is placed in the conductivity cell at
constant temperature. The temperature is maintained
constant with the help of the thermostat. Then the cell is
connected to the resistor box R and the alternating
current is passed through the cell with the help of
induction coil. Then the conductivity of the solution is
measured by the following equation:
• Conductivity of the solution = 1/resistance of the solution

31. • FACTORS AFFECTING THE CONDUCTIVITY MEASUREMENTS
• Temperature: The conductivity of the electrolyte increases with the temperature increase.
This is because of the ions mobility by increasing the temperature.
• Concentration of the sample solution: The concentration of the solution is inversely
proportional to the conductivity of the sample solution. The conductance is decreased
with the increase in the concentration. Hence diluted solutions are used for the
conductivity measurements.
• Number ions present in the sample solution: This is mainly based on the dissociation of
the compounds into ions. That is mainly of the number of ions present in the solution.
The number of ions present in the solution is directly proportional to the conductance.
Strong electrolytes completely dissociate into ions and have high conductance.
• Charge of the ions: Negative charge of the ions increases the conductivity where as the
positively charged ions decreases the conductivity.
• Size of the ions: The conductivity is inversely proportional to the size of the ions. That is
the increase in the size of the ions increases the conductivity.

32. • Types of the Conductometric Titrations
• Acid–base titrations: In this method, the conductance of
the hydrogen ions and hydroxyl ions are compared with
the conductivity of the sample solution.
• Strong acid with a strong base:
• For example, take the titration of the HCl with NaOH.
• [H+Cl−] + [Na+OH−] [Na+Cl−] + H2O
• The initial conductivity of the HCl solution is high because of the
protons from the dissociation of the acid. Then titrating with NaOH
dissociates into Na+ and OH−. This hydroxyl ion reacts with the H+
ions to form the water. This shows the decrease in the
conductivity. After completion of the reaction, the excess addition
of the NaOH shows the increase in the conductivity. The plot
between the conductivity and the volume of the titrant shows the
V-shaped curve.

34. • Strong acid with weak base:
• For example, titrations of the strong acid such as HCL
with the weak base such as the ammonium hydroxide.
• HCl + NH4OH NH4Cl + H2O
• Same as the titration of the strong acid with strong base,
it initially shows the increase in the conductivity because
of the H+ ions. This conductivity is decreased by the
addition of the weak base that is with the NH4OH that
neutralises the H+ ions with the OH− ions and decreases
the conductivity. The excess addition of the NH4OH does
not show the change in the conductivity. Then the plot
between the conductivity and the volume of the titrant
shows the plateau.

36. • Weak acid with a strong base:
• The weak acid such as acetic acid is titrated with the
strong base such as sodium hydroxide.
• CH3COOH + NaOH CH3COONa + H2O
• The acetic acid dissociates to produce the H+ ions which
shows the high conductivity and is titrated with the
sodium hydroxide which is dissociated to produce the
OH− ions which shows slight increase in the conductivity
by the formation of the CH3COONa at the equivalence
point. Then it shows the gradual increase in the
conductivity by the addition of excess titrant. Then plot
the graph between the conductivity and the volume of the
titrant which shows the plateau.

38. • Weak acid with weak base:
• The weak acid such as the acetic acid is titrated with the
weak base such as ammonium hydroxide.
• CH3COOH + NH4OH CH3COONH4 + H2O
• The acetic acid is dissociated and it combines with the
ammonium ion after dissociation of the ammonium
hydroxide. This forms the ammonium acetate salt which
shows the increase in the conductivity. After attaining the
equivalence point, the addition of the titrant does not
shows the conductivity change. The plot between the
conductivity and the volume of the titrant shows the
plateau.

40. • Precipitation titrations:
• When compared to the acid–base titrations, precipitate
titrations are not that much accurate because of the more
number of the interferences. These are also known as
the replacement titrations. The precipitate formation is
taken as the end point when the conductivity is
measured.
• Example: Potassium chloride is titrated with the
precipitating agent such as the silver nitrate solution.
• KCl + AgNO3 AgCl + KNO3

41. Initially the addition of the silver nitrate to the potassium
chloride shows the stability in the conductivity and the
excess of the silver nitrate addition increases the
conductivity because of the formation of the single
precipitate.

42. • In another case, the titration will form two precipitates.
For example, magnesium sulphate is titrated with the
barium hydroxide and forms two precipitates: the
magnesium hydroxide and the barium sulphate. Initially
the plot shows the decrease in the conductivity and then
shows the increase in the conductivity.
• MgSO4+ Ba(OH)2 Mg(OH)2 + BaSO4

43. • Redox titrations:
• In this method, the decrease in the hydrogen ions
concentration shows the decrease in the conductivity at
the end point.
• Example: The titration of the ferrous ions with the
dichromate ions.
• 6Fe+2 + Cr2O7 + 14H+ 6Fe+3 + 2Cr+3 + 7H2O
• The hydrogen ions show sharp decrease in the
conductivity. After the equivalence point, the addition of
the excess of the titrant shows the stability in the
conductivity.
•

45. • ADVANTAGES
• Appropriate for the dilute solutions.
• Broad selectivity.
• End point is determined by plotting the graph.
• No need for the specific conductivity.
• No need of indicator.
• DISADVANTAGES
• Less accurate when compared to other methods:
Because the high concentrations are not measured by
the conductometric titrations. The solutions are
compulsory diluted for the measurements.
• Less satisfactory when compared to other methods.

46. • APPLICATIONS
• Used in the determination of the basicity of the acids.
• The basicity is defined as the number of carboxylic acid
groups attached to the molecules.
• Used in the determination of the sparingly soluble salts
such as barium sulphate and lead sulphate.
• Used in the determination of the purity of the water.
• Used in the determination of the salinity of the sea water.
• Used in the determination of the ionic product of the
water.
• Used in the quantitative analysis of the compounds.

47. • REVIEW QUESTIONS
• What is the principle involved in the conductometry?
• What is the theory of conductometry?
• Explain the concept of molar conductivity.
• Explain the concept of cell constant.
• What are the different methods of conductivity
measurements?
• What are the factors affecting the conductivity
measurements?
• What are the different types of conductometric titrations?
• What are the different types of applications of
conductometry?