PA- I Non aqueous titration (HRB)

Non aqueous titration
1
PRESENTED BY:-
Miss.- Harshada R. Bafna.
M. Pharmacy.(Q.A.)

-Content-
 Solvents, acidimetry and alkalimetry titration.
 Estimation of Sodium benzoate and Ephedrine HCl.
9/14/2020 2Non-aqueous titration.(HRB)

A substance that dissolves a solute, resulting in a solution is
a solvent..
9/14/2020Non-aqueous titration.(HRB) 3
Solvent-
Alkalimetry titration
Acidimetric titration
Alkaline (basic)substance is titrated with standard acid is
acidimetric titration.
Acidic substance is titrated with standard base is
alkalimetric titration.

• Non aqueous titration are those in which titration of
weakly acidic or basic substances are carried out using
non aqueous solvents so as to get sharp end point.
• In this titration of substances dissolved in solvents other
than water.
• Many organic compounds are poorly water soluble or very
weakly reactive in water are titrated by non-aqueous
titration.
Non aqueous titration

Theory of Non aqueous titration
The principle and technique of this method is simple.
It is based upon the Bronsted- lowrey and Lewis theory
of acid and base and the nature of influence of levelling
effects of non-aq. solvents on substances.
The chemical reaction of HA with base B in aq. solution is
represented as…
HA + H2O H3O+ + A- Conjugate base of acid HA
H3O+ + B BH+ + H2O Conjugate acid of base BH

 However, in aq. solvents like glacial acetic acid, it can
accept the proton readily, when perchloric acid is used
as titrant.
HClO4 + CH3COOH CH3COOH2
+ (titrant)
CH3COOH2
+ + B BH+ + CH3COOH

Solvent
The solvents used in non-aq. titrations plays an important
role.
Generally, the solvent should be non-toxic for its wide
use in analysis; it should be liquid at the time of analysis.
 The organic solvents are used in non-aq. titrations
dependent on their properties such as capability of self-
dissociation, dielectric constant and acid base character
of solvent.

 Properties of organic solvent in non-aqeous titration-
1. Capability of self-dissociation -
Solvents can be classified as dissociating and non-
dissociating solvents-
 Dissociating solvent -
such as a) Ethanol to give ethoxide ion.
C2H2OH C2H5O- + H+
b) Acetic acid gives acetate ion,
CH3COOH CH3COO- + H+

 Some solvent dissociate without the production of
solvated proton
e.g. acetic anhydride -
It yields acetate and acetylium ion.
[CH3COO]2 O CH3COO - + CH3CO +
 Non-dissociating solvent -
1. It includes ethers, hydrocarbons.
2. These solvents may dissociate but it is not usually
detectable.

2. Dielectric constant -
 The dielectric constant (symbol: ε) of a solvent is a
measure of its polarity.
 The higher the dielectric constant of a solvent, the more
polar.
example : a) The dielectric constant of water is higher
than that of methanol; water is more polar than methanol.
Water- 78.5
Methanol- 32.6
Cyclohexane- 2.02.

3. Acid-base character -
a) In this the non-aqueous solvents can be classified
based on its proton donor-acceptor properties.
1. Protogenic solvent-
2. Protophilic solvent-
3. Aprotic solvent-
4. Amphiprotic solvent

Classification of Non aqueous solvent
1. Protogenic solvent
2. Protophilic solvent
4. Aprotic solvent

1. Protogenic solvent
 Acidic in nature and donate protons
 Ex:- sulphuric acid , formic acid, propanoic acid ,acetic
anhydride etc.
 They have high dielectric constant and ionised Because
of their strength and ability to donate protons.
2. Protophilic solvent
 Basic in character and react with acids to form solvated
proton
HB + Sol. ⇌ Sol.H+ + B-
Acid + Basic solvent ⇌ Solvated proton + Conjugate base of acid
 A weakly basic solvent has less tendency than a strongly
basic one to accept a proton.

 Amphiprotic solvents have both protophilic and
protogenic properties.
 Examples are acetic acid and the alcohols.
 They are dissociated to a slight extent
 The dissociation of acetic acid, which is frequently used
as a solvent for titration of basic substances, is shown in
the equation below:
CH3COOH ⇌ H+ + CH3COO−
 A weakly basic solvent has less tendency than a strongly
basic one to accept a proton.
 Similarly a weak acid has less tendency to donate protons
than a strong acid.
 Ex:-acetone pyridine liquid ammonia.

4. Aprotic solvent
Aprotic solvents are neutral, chemically inert substances
such as benzene and chloroform.
They have a low dielectric constant, do not react with
either acids or bases and therefore do not favour
ionization.
This type of solvents neither accept or donate protons
Ex:- Benzene, Dioxan, Chlorobenzene, chloroform,
ethyl acetate, carbon tetra chloride.

Solvent used in non aqueous titration
1. Glacial acetic acid:
 Glacial acetic acid is the most frequently used.
 Before it is used it should check water content, which
may be between 0.1% and 1.0 %. Just add sufficient
ethanoic anhydride to convert any water to the acid.
 The acid may be used by itself or in conjunction with
other solvents.
 Example, ethanoic anhydride, acetonitrile and
nitromethane.
2. Dioxane
 There is another popular solvent which is used in place
of glacial acetic acid.

3. Acetonitrile (methyl cyanide)
 Is frequently used with other solvents such as chloroform
and phenol and especially with ethanoic acid.
 It enables very sharp end point to be obtained in the
titration of metal ethanoate when titrated with perchloric
acid.
4. Alcohol
 Salts of organic acid especially of soap, are best
determined in mixtures of glycols and alcohols and
mixture of glycols and hydrocarbons.
 The most common combination is ethylene glycol
(dihydroxy ethane) with propan-2-ol or butan-1-ol.
 The combination provides admirable solvents power for
polar non polar end of molecules.

Determination of end point
There are two methods for determine end point.
1. Indicator method. 2. Potentiometry method.
1. Indicator method:
 The majority of non aqueous titration is carried out using
a fairly Limited range of indicators
 here are some typical examples.
 1. Crystal Violet: used as 0.5 % w/v solution in glacial
ethanoic acid. Its colour change is from violet through
blue, followed by green, then to greenish yellow, in
reaction in which basis such as a pyridine are titrated
with perchloric acid.
 2.Methyl red used as a 0.2% w/v solution in dioxane with
yellow to red colour change.

2. Potentiometric method:
 Potentiometric method for the detection of the equivalence
point.
 The end point is determined by using indictor electrode
(glass electrode) and reference electrode (saturated calomel
electrode).
 Potentiometric titrations involve the measurement of the
potential of a suitable indicator electrode with respect to a
reference electrode as a function of titrant volume.
 Potentiometric titrations provide more reliable data than
data from titrations that use chemical indicators.
 These are particularly useful with colored or turbid
solutions and for detecting the presence of unsuspected
species.

 A typical set up for potentiometric titrations is given in
Figure 1. Titration involves measuring and recording the
cell potential (in units of millivolts or pH) after each
addition of titrant.
 The titrant is added in large increments at the outset and
in smaller and smaller increments as the end point is
approached (as indicated by larger changes in response
per unit volume). Sufficient time must be allowed for
the attainment of equilibrium after each addition of the
reagent by continuous stirring.
 For this a magnetic stirrer with a stirring magnet bar is
used

 Apparatus for Potentiometric titrations can be classified as
1.Precipitation titrations 2. complex formation titrations
3.neutralization titrations 4.oxidation/reduction titrations.

Estimation of Sodium benzoate
 Introduction:
 Sodium benzoate is a white, crystalline or granular
powder or flakes.
 Its slightly hygroscopic, freely soluble in water, and
sparingly soluble in alcohol.
 The powder when dried contains not less than 99 % of
sodium benzoate.
 Sodium benzoate –
Molecular formula - C7H5NaO2
Molecular weight - 144.1

 Principle:
 Sodium benzoate has antibacterial and antifungal
properties.
 It is used as preservatives in pharmaceutical formulation.
 Sodium benzoate is salt derived from a weak acid and a
strong base, so its aq. solution is alkaline.
 Therefore solution containing sodium benzoate is assayed
using a standard N/2 hydrochloric acid solution in an
non-aq. titration.

 Procedure:
 Wash the burette with distilled water and then rinsed
with a little solution of the titrant (HCl).
 Fill the burette with N/2 HCl to level.
 Pipette out 10 mL of an unknown sodium benzoate
solution in a clean conical flask. Then add 25 mL of
distilled water, 15 mL of ether and add 3 to 5 drops of
bromophenol blue as a indicator.
 Start titration by adding HCl dropwise with shaking the
aqueous and ethereal layer until a green colour persist in
the aqueous layer (end point)
 Note down the BR reading or record the volume of HCl
used.

Calculation:
Factor:
Each mL of N/2 hydrochloric acid is equivalent to 0.07205
gm of (C7H5NaO2) Sodium benzoate.
 Result: The percent purity of the given sample of sodium
benzoate was found to be------------
Vol. of HCl X factor X 100 X N of HCl (Actual)
Percent purity of C7H5NaO2 =
Weight of C7H5NaO2 in gm. X N of Hcl (Expected)

Estimation of Ephedrine HCl
 Introduction:
 Ephedrine hydrochloride is a phenethylamine found in
ephedra sinica.
 Pseudoephedrine is an isomer.
 It is a neither alpha- and beta-adrenergic agonist that may
also enhance release of nor epinephrine.
 It has been used for asthma, heart failure, rhinitis, and
urinary incontinence, and for its central nervous system
stimulatory effects in the treatment of narcolepsy and
depression.

Principle:
 The assay of ephedrine hydrochloride belongs to titration
of halogen acid salts or bases under non aqueous titration.
 The halide ion is too weakly baric to react quantitatively
with acetous perchloric acid.
 Addition of mercuric acetate to a halide salt replaces the
halide in by an equivalent quantity of acetate ion, which is
a strong base in acetic acid.
Reaction:
2C10H15 ON. HCl 2C10H15 ON+H + 2Cl -
(CH3COO)2 Hg + 2Cl Hg2 Cl2 + 2CH3COO -
2CH3COOH2 + 2CH3COOH 4CH3COOH
(Onium ion) (Acetate ion) (Acetic acid)

 Procedure:
 Weigh accurately about 500 mg of ephedrine
hydrochloride and dissolve in 25 mL of glacial acetic
acid and add 10 mL of mercuric acetate solution.
 Mix and titrate the contents with N/2 acetous perchloric
acid using solution of crystal violet as indicator, until the
colour changes from blue to green.
 Repeat the titration for concordant values.

 Calculation:
Factor:
Each mL of 0.1HClO4 (perchloric acid) is equivalent to
0.020107 gm of ephedrine hydrochloride.
 Result: The percent purity of the given sample of
ephedrine HCl was found to be------------
Vol. of HClO4 X Factor X 100 X N of HClO4 (Actual)
Percent purity of ephedrine Hcl =
Weight of ephedrine HCl in gm. X N of HCl (Expected)

9/14/2020 30
References
1. A Textbook of Pharmaceutical Analysis (volume – I) by
DR A V Kasture, DR H N More, DR K R Mahadik, DR
S G Wadodkar, Nirali Prakashan, Pg.no. 73-84.
2. A Textbook of Pharmaceutical Analysis by David. G.
Watson, Churchill Livingstone, Pg.no. - 56
3. www.google.com.

PA- I Non aqueous titration (HRB)

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