Acid
Base Titration
In
chemistry acid base titration are used for analyse the
unknown organic compound concentration of an acid and base.
Principle -Titration is based on
neutralise the reaction through acid and base
Indicator- Phenolphthalein is the most usable
indicator for acid base titration.
Reaction
- Reaction are
involved to transfer of proton Eg. Base accepted proton from acid.
Equivalent point- moles of H+ are equal
to the moles of OH-
During
titration- Acid is
taken in burette to the known volume of base in a conical flask to make the
equivalent point (endpoint) of titration.
Theories:-
1. There are three theories-
1. 2. Arrhenius
theory
2. 3. Bronsted
lowry theory
3.
4. Lewis theory
Acid- According to this theory those
substance which produce free hydrogen ion in an
aqueous solution are called acid.
Base- According to this concept, those
substance which produced free hydroxide (OH-)
ion an aqueous solution.
Eg- HCL,HNO3, H2SO4, CH3COOH etc.
Where, Hcl
is arrhenious acid
NaOH is Arrhenius base.
2. Bronsted
lowry theory –
This theory are introduced by J.N Bronsted and J.M lowry in 1923.
Acid- According to this theory those
substance which have tendency to donate proton (H+)
by any method in any solvent. Eg; Hcl
Base- According to this theory, those
substance which have tendency to accept proton (H+)
by any method in any solvent are called base. Eg- CL, O2 etc.
3. Lewis
theory- This
theory are given by G.N Lewis in 1930
Acid- According to this theory, those
substance which have tendency to gain electron pair (cation).
Base- According to this theory, those
substance which have tendency to donate electron pair (anion).
Overviews of theory’s:-
|
Theory |
Acid
|
Base
|
|
Arrhenius
|
H+
Producer |
OH-
producer |
|
Bronsted-
Lowry |
H+
Donor |
H+
acceptor |
|
Lewis
|
Electron
pair accepter |
Electron
pair donor |
Neutralisation
curves
A reaction
in which an acid react with base to produce salt or neutralise base is called
neutralisation reaction.
Neutralisation
curve are plotted as follows-
· 1.Weak
acid & Strong base
· 2. Strong
acid & Strong base
· 3. Strong
acid & Weak base
· 4. Weak
acid & Weak base
I. 1. Weak Acid & Strong Base
I. v ஃ In this titration weak acid (acetic acid) is treated with strong base (sodium hydroxide) by using indicators (Thymolphthalein, Phenolphthalein, Methyl red, Methyl orange) to detect the endpoint.
v ஃ During
titration weak acids dissociate slowly and strong base are dissociate rapidly.
v ஃ Initially, PH is Normal during reaction process, So curve will not raise much It’s called half neutralisation point.
ஃ The PH is rises due to presence of excess amount strong alkali.
II. 2. Strong acid & Strong Base
v ஃ In this titration, the substance take 50ml of a strong acid (HCl- 0.1M) and strong base (NaOH-0.10M) are reacted with each other by using indicator (Phenolphthalein , Bromothymol blue, Methyl red).
v ஃ Acid
and base are fastly breakdown in cation and anion and react with each other to
form salt and water.
v ஃ During starting PH slowly rise due to presence of excess of alkali pH is rises fast.
3. Weak Acid & Weak Base
v
In
this titration weak acid {ethanoic acid (CH3COOH)0.1M} is treated with weak base {aqueous ammonia (NH4OH) 0.1M}by using mix indicators (red methylene blue mixed).
v
Main
features of change the PH curve near equation point and neutralised slowly.
v
So
the end point are not detect by any single indicators, for detection mixed indicator are used.
v
Eg.
Bromothymol blue and phenol red, cresol red and Thymol Blue.
IV. 4. Strong
acid & Weak Base
v ஃ In this titration strong acid(HCl) is treated with weak base (aqs. ammonia solution) with the help of indicator (Phenolphthalein , Bromothymol blue, Methyl red, Methyl orange) to detect the endpoint.
v ஃ During
this titration base are dissociated slowly and strong acid are dissociate
fastly.
v ஃ In
Initially, PH is normal and curve will not raise, So this is called half
neutralisation point/curve.
v ஃ Sharply rises the PH due to presence of excess amount of strong alkali substance.
NON
AQUEOUS TITRATION
The Titration
is involving very weak acid or base with the help of non-aqueous solution to
determine correct end point.
Principle- some acid and bases are insoluble
or very slow soluble in water and the can’t analysed during titration method so
no- aqueous solvent are used to proper dissolve the sample.
Non aqueous solvent
The nature
of solvent are decided the behaviour of acid and base. If any solute dissolved
in any given solvent with acidic or alkaline nature.
Characteristic-
Non
aqueous solvent have mainly two characteristic role in non-aqueous titration-
·
The
solvent should be non-toxic
·
It
should be liquid during analysis
Types of solvent - Generally, organic
solvent are used in the non-aqueous titration. The non- aqueous solvent can be
classified based on the proton donor or acceptor properties.
On the acid base properties of the solute they are
classified in four types:-
1. 1. Aprotic
solvent
2. 2. Protophilic
solvent
3. 3. Protogenic
solvent
4. 4. Amphiprotic
1. 1. Aprotic
solvent: These
solvents are generally chemically neutral and hydrocarbons or
chlorinated hydrocarbons.
These solvents not contain any proton or
hydrogen Example- toluene, carbon tetrachloride, acetone, chloroform,
benzene etc.
2. 2. Protophilic
solvents: These are basic in nature and react
with acid to form the soluted proton. It shows the greater tendency to the
accepting the proton and have high di-electric constant. Eg- water,
alcohol.
3. 3. Protogenic
solvents: These
solvents have more acidic character and have high affinity for donating protons
Example, alcohol, organic acid, hydrogen fluoride H2SO4 (These are
strong acid and act as proton donor it is important to enhancement of the
strength of weak base).
4. 4. Amphiprotic
solvent- These
solvents like water, alcohol and organic acid (weak) act as amphiprotic solvent.
These solvent causes both acidic and basic
properties and high dielectric constant
Or
These solvent have the ability to
donate, as well as accept the proton, because they contain both protogenic and
protophilic properties Example, water, ethanol, isopropyl alcohol, etc.
|
Solvents |
Properties |
Example |
|
Aprotic |
Neutral ( not
contain protons& hydrogen) |
Toluene,CCl4 |
|
Protophilic |
High affinity to
accept protons |
Pyridine, NH3 |
|
Protogenic |
More acidic
character, high affinity to donate protons. |
Hydrogen fluoride,
H2SO4 |
|
Amphiprotic |
Protogenic+
Protophilic |
Water ,NH3, ethyl
alcohol |
Indicators
for non- aqueous solvent- Methyl red, Naphthol benzene, Thymol blue, etc.
Advantages-
·
Acid
and base are easily soluble in non- aqueous solvent.
·
Non-
aqueous solvent can dissolve in two or more acid.
·
The
biological ingredients are selectively titrated with suitable solvent or
indicator in acidic or basic medium.
·
Non-
aqueous titration are comparatively simple and accurate.
Application- By the use of non-aqueous titration determined as
follows-
·
%
of purity
·
Hydrophobic
·
Steroid
·
Anti-tubercular
·
Phenobarbitone
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